A Critical Examnation Cf Sore Aspects of the Analytical

A CRITICAL EXAMNATION CF SORE

ASPECTS OF THE ANALYTICAL

CHEMISTRY OF BISMUTH.

A Thesis submitted to the University of London for the degree of Doctor of Philosophy

by JOHN AUSTIN CLEMENTS. ACITOWLEPG

Most of the work described in this thesis was carried out from 1954 to 1956 in the Analytical Chemistry Peparbnent of the Royal College of Science. The candidate is indebted to Assistant Professor L.S. Theobald both for suggesting the initial problem and for super. wising most of the work described in the thesis. The candidate also wishes to express his thanks to Mk. P.E. Croft for carrying out the spectrographic work described in the last section of part II. Zrrt ACT.

The first part of the thesie is a review of the literature related to the analytical chemistry of bismuth. The second part of the thesis is en account of the practical work carried cut by the candidate and is divided into three sections. Section one describes the critical investigation and modification of the gravimetric phosphate method era an investigation of volumetric E.P.T.A. 'methods far the determination of bismuth. Section two describes the work carried out on methods of separation. neral !methods of separation investigated were the volatilisation, of broid+es from perchloric acid solutions and the precipitation of bismuth ae ide metal and sulphide. Several methods of separation are described far aaci c elements, e.g. the preciPitation of ,tellurian bylsearis of a mixture of hydrasine and sulphur dioxide. Section three describes methods for the analysis of alloys and ores. Some results obtained by these methods are reported. The behaviour of some elements present in complex materials has been follaaed by a semi-quantitative spectrographic method. The separations and the preparation of the samples were carried out by the candidate, but the actual spectrographic analysis was performed by 1,9b%. P.E. Croft under the candidate's supervision. The final part of this section is a critical discussion of the methods developed. In Appendix I are mentioned some methods that were cursorily exasined but were abandoned for the reasons that are given. In Appendix II are given the calibrations of the weights and the volumetric glassware used. The weight-history of two porous-based Berlin porcelain crucibles aver a period of two yearn in also recorded. The final pages contain the bibliography. INTRODUCTION • 1 Lau. THE LITMATURE RnATED 21 BISMUTH ANALDSIS 3 Introduction 3 Gravimetric Methods 4 Volumetric Methods 25 Colorimetric Methods 38 Methods of Separation 44 Summary artful Literature and Selection of Methods for Investigation 53 PART II. EIGVIINENTAL WORK 55 Apparatus and Materials 55 Section-(i) Methods of Determination 58 Introductory Work '58 Examination of the Bismuth Phosphate Method 66 Examination of the EsDa.A. Titration 109 Section (ii) Separation Methods 129 Volatilisation of Volatile Bromides from Perchlorio Acid Solutions 129 Preparation of Bismuth by Means of Hydrogen Sulphide 139 The Cementation of Bismuth an Zinc Powder 141 The Precipitation of Bismuth Oxybromide 151 Other Separations 160 Separation of Indium 161 Separation of Tellurium 163 Separation of Copper 164 Section (iii) Analysis of Ores and Alloys 167 Spectrographic Method 167 Analysis of Alloys 168 Analysis of Ores 174 Discussion of Methods 182 APPlarint I 186 APPENDIX II 188 REVERE= 192 zup/ormarkov

Although this thesis is primarily concerned with the analytical chemistry of bismuth it is advantageous to, outline very briefly the occurence of bienuth and its major uses in industry. The elements with which bismuth occurs and with which it is used in its industrial applications obviously decide the analytical separations that are of the most importance; the latter also decides to sane degree the accuracy that is required in a quantitative determination. Opcurence of Bieriut)).

Economicall the most important eral is biemuthinite or bismuth glance 3i283. Other economically important minerals tires.* the native metal, bismuth ochre cr bienite 131203, bismutite (8i0)2CO3H20 and several complex lead and tellurium sulphides. It is, however, unusual to find any simple bismuth mineral in workable anounte; the bilk of the world's supply

is obtained as a by-p.roduct from the recovery of other metals and ores of other metals, such as those of copper, lead, tin, cobalt, gold, silver and tungsten. Uses of Biemuth. Before 1930, the major use of bismuth compounds was in the pharna.. ceutical industry, but, at the present time, the major consumption of bismuth is in the production of fusible alloys. Dienuth is added in small amounts to iron, steel, stainless steel, manganese steel and aluminium

alloys to produce castings and forgings that can be easily machined. Alleys of bismuth with elements mch. as tin, lead, c antimoqy are used in fire.detection appsTatus, fusible elements in automatic sprinki. ler heads fire.iticar release links, automatic ealut-seffs for gas an/ electric water-heaters and safety plugs in compressed gas cylinders. rliscellaneous uses of bismuth, bienuth compounds or bisTruth alloys Ares- casting production of accurate patterns,• proof castings of forging dies, plastic moulds, moulds for wax models for precision casting, conotant temperature baths, liquid seals for fUrnaces, hydraulic liquiOr in heavy eL-vipmest, fil3.1np., thinovelalled tubes far accurate bending r in certain types or emmunition, in cosmetics, dentistry and ceramics. Recently, bismuth has been used as a heat-exchange liquid in atomic reactors and in the production of atomic weapons. PART

THE LITMATTIE ET:MATED TO BISIUTH ANALYSIS

I 9DUCTI0N. As the main object of thin work was to cotablish an accurate umpire method of analysis, qualitative methods and physical methods as a whole are not considered. However, for the sake of completeness coiorimetric methods have been included. The following survey can conveniently be divided into four sectionst— (1) Gravitetric methods, (2) Volumetric methods, (3) Calorimetric methods and (4) Methods of separation. It will be appreciated that cone overlapping is essential, for instance, the precipitation of bismuth as phosphate has been used to separate bismuth from other metals and is also the. basin of volumetric, calorimetric and gravimetric methods of determining bismuth. The literature has been reviewed in detail from 1900 to the present time; any important papers published before 1900 are also included. The literature on bismuth analysis is very extensive, and for this reason papers just reporting the application of standard methods to a particular problem are not mentioned unless some modification is introduced by the author, or he presents useful information regarding such things as accuracy or interference from other elements GRAVIMTBIC =NOM. (1) Bismuth phosphate. Bismuth phosphate wee first used in quantitative analysis for the determination of phosphate by precipitation by an acid solution of bismuth nitrate(1). Salkowmki(2) suggested in 1868 that bismuth could be determined by precipitation as bismuth phosphate, tut he did not publish a method until much later. The first published method is that of Stachler and Scharfenbcrg(3) who precipitated the bismuth from a nitric acid solution by addition of a ten per cent. solution of trisodium phosphate in water; the phosphate solution was added until the solution was only just acid. If hydrochloric acid was present awry large excess of sodium phosphate solution was necessary for complete precipitation of the bismuth. The authors claimed a separation frcel copper, cadmium, silver and mercury. Lead was coprecipitated, but. the authors suggested that the coprecipitated lead phosphate could be removed by digestion of the precipitate in one per cent, nitric acid. In the same journal Saikawski(4) published results obtained for the determination of bismuth as phosphate in the presence of copper, cadmium, mercury, silver, lead, iron, manganese, cobalt, nickel, zinc, chromium and aluminium. Unfortunately, the author did not publish the method he used. The following year a method was published by Moser(5) who used N/5 ammonium phosphate solution to precipitate the bismuth as phosphate fray a dilute nitric acid solution. The method separated bismuth from copper and cadmium, but not from lead. In 1907, Staehler(6) published a modification of hits method in which he added phosphoric acid to the nitric acid solution before adding the sodium phosphate solution to precipitate the bismuth. This meant that when the bismuth was precipitated the concentration of phosphate ions VMS much greater than in his previous method, end hence the separation fron chloride was better, i.e. lase basic chloride was copreci— pitated. No new work appears to have been done on the phosphate method during the next thirteen years, although two papers were published that reported satisfactory results with the methods already publiehed(7, Little and Cahen(6), who used the method of Staehler(19, obtained excellent results with this method; they noted, hop/ever, that the bisiuth phosphate was hygroscopic. Galletly aria Nenderson(9) inveztigated Staehler's proposed method for separating biseuth from lead, but found it to be unnatinfacteey. In 1920, Schooner and Waterhouse(10) presented a phosphate method for the determination of bismuth in bismuth ores and minerals. In this method the bismuth was precipitated from a fairly concentrated nitric acid solution by annonium phosphate solution, and the nitric acid concentration was reduced after precipitation by diluting the solution with water. The effect of other ions was not investigated as the bismuth was separated from all other ions before precipitation as phosphate. Three years after Schooner's work was reported, Luff(11) published the results of a thorough investigation of the phosphate method. The nitric acid concentration used by Luff was very high, but he was the first to real— ise the advantage of making the annonitri phosphate precipitant acid with nitric acid. The concentration of nitric acid was 5m1. of concentrated nitric acid in every 100m1. of final volume. The author claimed that the method womad separate bismuth from copper, cadmium and lead. In the following year, he published another paper(12) describing the separation of bismuth from silver, manganese, zinc, nickel, cobalt, iron, aluminium and magnesium. To effect these separations Luff altered the amounts of nitric acid and annonium phosphate used. In 1929, Solodovnikov(I3) investigated the method of Moser(5) and found that it gave satisfactory results even in the presence of organic matter. Blasdale and Parle(14) published a study of the phosphate method in 1936; they decided that the large excess of annordun'phwphate used by Schoeller and Waterhouse was unnecessary. Their final solution was 0.2N with respect to nitric acid and 0.2U with respect to annonium phosphate. They obtained a separation from sodium, potassium, magnesium, zinc, copper and cadmium, but not from load . The next year 'Schoeller and LaMbie(15) published cane observations on the method published by the senior author and Waterhouse(10). The most important of these was the Interference of sulphate with themethod'- surprisingly large amounts of sulphate were coprecipitated with the bismuth phosphate. Recent confirmation of this has been published by Belcher et al. (16) in a paper describing the volumetric determination of sulphate with 4-amino-41..chloro-diphenyl hydrochloride. The most recently published work on the determination of bienuth ac phosphate is that of Silverman and Shideler(17) Who precipitated the bismuth by means of a solution of ammonium phosphate from a nitrie.perchloric acid solution., The pH of the solution and of the precipitant was adjusted to

0.6 before precipitation. Although conditions vary greatly in the proposed methods and there is disagreenent about the feasibility of making sane separations, the foil:w- ing generalisations can be made:-

(a) The best precipitant is asmonium phosphate, preferably malls acid with nitric acid.

(b) The method probably gives a separation from the, alkali metals, magnesium, zinc, nickel, cobalt, manganese, aluminium, copper, cadmium, silver

and mercury, but not free lead. (c) Interference fran the elements of the analytica3. Group. 11B has not been investigated. (d) Anions other than nitrate or perchlorate interfere with the method (2) Favtralytic Methods. The.electrolytic determination of bismuth as the metal is the most

extensively studied of all the gravimetric methods of determining bitruth. In spite of this, the method has not found favour in industrial laboratories. One of the earliest papers published on the electrolytic determination of

bismuth was that of Vortmann(18) who described the deposition of bismuth true a nitric acid solution. In 1900, Balachowski(19) published a method for the deposition of bienuth frcr a nitric or sulphuric acid coliftion. To improve the adherent properties of the deposit he used roughened electrodes and prolonged electrolysis with a Lee current; eight hours were required for deposition. The next year Wirenenauer(20) published a method for depositing

bismuth from a nitric acid solution; he was able to reduce the nitric acid concentration and still keep the bismuth in solution by, using.glycerol as a complexing ageeit. The time required for deposition was three hours. '.unck(21) preferred to use wire-gauze electrodes. In 1904, Hollard. and Bertiaux(22) separated bismuth as phosphate, issolved the precipitate in concentrated nitric acid and evaporated the solution to fumes with sulphuric acid) this solution was used for the electrolysis. If lead was present it was precipitated as the sulphate, alcohol was added and the solution was electrolysed in the presence of the lead sulphate.. The time required for a deter ination was considerably reduced by Metzger and I3eana(23) who used a rotating cathode and an acetic acid-boric acid solution. Peset(24) deposited bismuth from a Sulphate, solution and then protected the deposit by plating a known weight of cadmium over it. He preferred to use a rotating anode to prevent deposition of bismuth peroxide. The first method in which a chloride solution was used was that published by Schoch and 13rcem(25) in 1912; they used hydrcepelanine as a reducing agent. - The time required for deposition of the bismuth VIras very short e. about twelve minutes The next year, a paper by Richardson(26) described the first electrolytic separations of bismuth from other metals. The author vial able to separate bismuth from lead in the presence of tartaric acid and frart, cadmium in the presence of lactic acid. The use of tartaric acid solutions was also studied by Poch(27) who investigated the use of nitric, sulphuric and acetic acid solutions as well ae atenoniacal solutions. He also studied the use of various types of electrodes. Engelenberg(28) deposited bismuth on a platinum gauze electrode and then protected the bismuth by depositing a known weight of copper on top of it. Lassieur(29, 30) described the electrolytic determination of bismuth in hydrochloric acid-hydrovlamine hydrochloride solutions. Silver was deposited first by controlling the potential, copper was then removed by electrolysis in ammoniacal solution and bienuth was determined after acidification of the solution. Seal(31) was able to separate bismuth from lead by electrolysis at a cathode potential of 0.5v. to 0.75v. in a solution containing glucose and four per cent. by volume of nitric acid. Jilek and Lukas(32, 33) deposited bismuth from a fluoride-borate solution. They added potassium citrate when hydrochloric acid was present. The same. year Collin(34) pUblished'a modification of the method of Sand(35). A review of electrolytic methods of determining bismuth was published by Chetverikov(36) in 1930. A separation of tin and lead from bismuth was published in 1939 by Kny-Jones(37). He used a hydrochloric acid solution containing hydrazine and oxalic acid; the electrolysis was carried out at a controlled potential. The techniques used by this author, i.e. controlled potential electrolysis with platinum gauze electrodes in the presence of organic complexing agents, are typical of many such processes that have been published in recent years (38, 39, 321, 322, 323, 321, 325). In conclusion, it may be said that the electrolytic method of determining bismuth is not much used although a large amount of work has been done on it. The main drawbacks to the method are lack of selectivity, poor adherent properties of the deposited biemuth and a tendency for the metal to oxidise during drying.

(3) Bianuth Metal try. Reduction. This method was first proposed by Vanino and Tredbert(40) in 1898. The reduced the bienuth to the metal by an aqueous solution of formaldehyde in alkaline solution. The bismuth metal was filtered, washed, dried at 105°C. and weighed. The method was investigated by Tallantyre (41) who claimed satisfactory results, although there was a tendency for the results to be high. This fact was confirmed by Kurtenacker and Werner(42) who also tested hypophosphorous acid as a reluctant, this redustant having been proposed by Mhtbnann and Mawroa(43) in 1897. More recently hypophosphorous acid has been reinvestigated as a reduetant by Bomberger(326). Rupp and Hamann(44) showed that the high results obtained with the formaldehyde method were due to incomplete reduction of the blemuth oxide to the metal. If the precipitate was heated in hydrogen at 200°C., excellent results were obtained. A similar process to that of Vanino and Treubert was publiahed by Cousin(45), who reduced the bismuth salt in alkaline solution by means of glucose. This method suffers from the disadvantage that nearly all other metals interfere and must therefore be absent; thus the applications of the method are very limited. Tallantyre and Cousin were both aware of this limitation and both recannended the method for the rapid determination of bismuth in pharnaceutical-grade bismuth salts. (4) Basic Bismuth Carbonate.' Rose(150) appears to. have been the first to have used the precipitation of bismuth as basic carbonate by ammoniun carbonate solution as a means of determining bismuth. Fresenius(151) also- described a method in his Hand— book. The method is very simple, and consists of precipitating the bismuth as carbonate from a nitric acid solution by a solution of ammonium carbonate; the solution in best neutralised with aqueous ammonia if a' large amaant of free acid is present. The bismuth can also be precipitated as the basic carbonate by a solution of sodium or potassium carbonater but the precipitate is contaminated with alkali metal ealts(46). Schoeller and Lanbie, }mover, preferred to precipitate the bismuth with a solution of sodium carbonate, as this method of precipitation gives a better separation from sulphate (15). The precipitate is soluble to some extent in an excess of ammonium carbonate solution and in an excess of aqueous,atmonia(47, 48). Methods have been reported in which the. bismuth isiaeighed as the carbonates an early method in which this procedure loused is that of Seubert and lten (49), and a more recent one in that of Hecht an&Reissner(50), The elements that interfere in the basic carbonate method are numerous; copper it one of the few elements which is not supposed to be precipitated (48). Castanares(7) obtained a separation of bismuth from mercury by the basic carbonate method. Most authors, however, prefer to separate all other elenents before precipitating the bismuth by ammonium carbonate eau tion(51, 52). The method is capable of giving very accurate results when applied to a pure nitric acid solution of bismuth if the proper precautions are taken to avoid an s eas ofalmonia or ammonium carbonate, i.e. if a itable indicator such as methyl red is used. Care is also needed in iepiting the Terecipitate, which must not be ignited in the presence of filter paper or other organic matter. The precipitate is beet left to settle and re— crystallise and then filtered on a Gooch crucible. The main, disadvantages or the method are that it ie nob selective, the precipitate is by no, means an ideal precipitate to work with, and enall amcunts of sulphate* chloride and bromide interfere as do practically all anions ether than nitrate. Sulphate causes high results because basic bismuth sulphate is precipitated and not all the sulphur trioxide le lost on.ippition. Halides cause loo results because basic halides are precipitated and these deconpone on ignition to the oxide and the trihalides, which are volatile. 3BiOX ---e B1203 -4- 81X3 An in practical analysis i.t is difficult to avoid snail anountn of sulphate and chloride, the method is of limited application. (5) Plasie Biemith Chloridt 'This method is another of the ter earivmothods of determining bienuth and is to be found in the early handbooks of Fresenius(151) and of Rose(150). These methods were based on the work of Arppe(53). The method of precipitation of the bismuth ceychloride has been altered by various workers. Some authors prefer to dilute the hydrochloric acid solution of the bismuth with uater(54, 55, 57), while others prefer to use a nitric acid solution and to precipitate the bismuth ovarchloride by a volu— tion of °mantel chloride(%) or diluted hydrochloric acid(4C). The method was thoroughly investigated by allenik are Kuhn(57) Who 13

obtained results that were within 0.2 per cent. of the theoretical.. These authors diluted a hydrochloric acid solution of the bismuth.mith water. More,recently, the method was tested by Sarudi(58) who found that the results were dependent on the concentration of the bismuth; he found that with a bismuth concentration of 0.1g. per.100m1. of solution there-. cults lir= loo, but with a bismuth concentration of 0.05g. per =Mi.,. the results mere very good. • The oxychloride method forms the.basis of many industrial methods of ore analysie(59, 52, 60, 61) and is to be found inmost standard texts on inorganic analysis(48, 62, 63, 64, 65),, Thus, the oxychloride method is probably a moderately accurate method and is much less likely to be affected by mall amounts of other anions and cations than is the basic carbonate method. A slight disadvantage of the method is that six to twelve hours are needed for complete precipitation of the bismuth.

(6) ?epic Hi m0 Tod 4Q* This method was first described by Strebinger and Zinc in 1927. They published both a macrosmethod(67) and a micro.method(66). The authors. treated the dilute nitric acid solution of the bismuth with a slight excess of solid potassium iodide over that required to precipitate the bismuth as the tri4odide (i.e. until the supernatant liquid was just pale,yellaw) and then diluted the solution with water. This solutionwas.boiled to, convert the black tri-iodide to the golden coloured basic iodide. The solution was neutralised to methyl orange with a solution ofammoniumacetate. The authors claimed a separation from lead and, in a, later paper by Strebinger and Ortner(68), a separation froM cadmium. The method. of Strebinger and Zinn was investigated by Hecht and Reisener(69) who considered it to be not very accurate. They preferred to do the final neutralisation with aqueous ammonia instead of ammonium acetate solution. An independent me aims proposed more recently by Kakita(70) who adjusted the pH of the solution by the slew hydrolysis of hexaine. The method has not been tested sufficiently for any real conclusions to be drawn as to the accuracy obtainable or as to the separations that are possible. (7) Baaic Bismuth =pate. The first method based on the isolation of basic bismuth nitrate was published by Lowe(71) in 1856. The nitric acid solution of the bismuth was evaporated until the residue was of a syrupy Consistency, hot water wan added and the solution was again evaporated; the process was repeated three or four:times.' . ,The' basic nitrate was filtered, washed with ammonium trate solution and ignited to'the oxide for weighing. Several workers have reported excellent results 'with Lowegemethodi but it is tedious and requires very care/Nil work to obtain accurate'results(72, 73, 74). The method is applicable in the presence of copper, CadmiUm and lead. Several methods of precipitating basic bismuth nitrate have been re. ported, the first of these was published by Daff(74) in 1920. In this method the solution was boiled with a mixture of annonium nitrate and sodium nitrite when the basic nitrate was predipitated. The precipitate was washed with ammonium nitrate solution, but as the' precipitate was always -.15..

contaminated 4th silica and alkali metal salts it could not be ignited to the oxide and weighed. In 1923, the same authOr(75) published another method in which the nitric acid solution of bismuth was neutralised to methyl orange with solid sodium hydrogen carbonate, a standard amount of acid was added and the solution heated to boiling. A slight deficiency of sodium carbonate solution was added, drop by drop, over a period of one hour. The precipitate was allowed to settle, filtered and washed as before. Both these methods separate bismuth from copper, cadmium and lead. Blumenthal(%) precipitated bismuth oxynitrate from a solution that was just acid to methyl, orange by the addition of mercuric oxide. The solution was allowed to stand for twelve hours, the basic bismuth nitrate and the excess of mercuric oxide were filtered, washed with 0.1 per cent. potassium nitrate solution and ignited to the oxide for weighing. The excess of mercury was volatilised during the ignition. Blumenthal claimed that lead did not interfere with the determination of bismuth in, this way. These methods are of little practical value and do not find any ready applications. Their weakness is that virtually any anion other than nitrate interferes, not only by the precipitation of the corresponding bismuth salts, as outlined under the basic carbonate method, but also by the precipitation of salts of the other metals present. (8) Bismuth Sulphide. The determination of bismuth as sulphide is perhaps the oldest method of determining bismuth; the first method was published in 1841 by Rose(77). Early work on the determination of bismuth as the sulphide was done by Lowe (78) who removed free sulphur from the precipitate by means of a concentrated solution of sodium sulphite. The precipitate was washed and dried at 105°C. The excess of sulphur in more quickly removed by washing the. precipitate with alcohol, ether, carbon disulphide, alcohol and again with ether. The precipitate is dried at 105°C. and weighed(79). 'loser and Neusser(80) preferred to heat the precipitated bismuth sulphide in a stream of hydrogen sulphide at 270°C. They claimed that air-drying, led to oxidation of the precipitate with the formation of sulphate; the precipitate could also be dried in a stream of carbon dioxide. Recently, Flaachka and Jakobljevich(81) used thioacetamide to precipitate bismuth as the sulphide from hydrochloric acid, nitric acid and amonimm hydroxide solutions. Taimni and Salaria(82) precipitated bismuth by a freshly prepared solution of hydrogen sulphide in 2N-sodiun hydroxide solution, or in 2N-asmonium hydroxide solution. The authors claim that the precipitate is free from an excess of sulphur. The precipitate is washed and then dried at 105°C. If the bismuth is precipitated from a hydrochloric acid solution, the acid concentration is very critical. According to Manchot et al.(83), biernuth was quantitatively precipitated as bismuth sulphide by hydrogen sulphide from solutions that contained up to 14g. of hydrogen chloride per 10D711. (about 4N); no precipitation occurred from solutions that contained , 16g. of hydrogen chloride per 100m1.(about 4.5N). However, Ramachandran (84) stated that the precipitation of bismuth sulphide by hydrogen sulphide began when the solution contained 25 per cent. by vollime of concentrated hydrochloric acid(about 3N) and was complete at concentrations below 16.66 per cent, by volume of concentrated hydrochloric acid(about 211). Lundell 17 -

and HoffMann(85) stated that the precipitation of bismuth was nearly complete in 3N-hydrochloric acid, and was complete in 2N-hydrochloric acid. The solubility of bismuth sulphide in hydrochloric acid is very temperature dependent and this may account for the differences reported above. Bismuth sulphide is partially precipitated from 36N-sulphuric acid (85) and is completely precipitated from 18N-sulphuric acid(85„ 86). Bismuth sulphide is partially soluble in solutions of alkali sulphides and hydroxides, but is insoluble in solutions containing ammonium sulphide and ammonium hydroxide(10, 48). (9) Bismuth Sqlenitl. The determination of bismuth as selenite was first proposed in 1930 by Berg and Teitelbaum(87). They precipitated the bismuth from a solution that was 0.25N to 0.33N with respect to free nitric acid. The precipitant was a solution of selenium dioxide in water. The precipitate obtained trim cold solutions was 812(3e03)3.H20; on boiling the solution, the precipitate recrystallised and became anhydrous. The precipitate was filtered, washed with cold water, dried at 1050C. and weighed as the anhydrous selenite. The method was thoroughly investigated by Funakoshi(88, 85) who stated that the solution should not be more than 0.5N with respect to free nitric or hydrochloric acid, although somewhat more sulphuric acid Was permissible. The author claimed that copper, cadmium, ferrous'iron, aluminium,.nickel, cobalt, zinc, manganese, calcium, lithium, sodium and potassium did not interfere. Interference was encountered from ferric iron, chromium Mercury, lead, tin, atimony,silver, barium, strontium, magnesium, thorium and titanium.

Funakoshi preferred to ignite the prodipitate to the oxide for weighing rather 18 — than to Weigh the precipitate as the selenite.' A' recent investigation of the method has been made by' Sant and Varkey(327), (10). Bistath .Tellurate. Thismethod mes'pnblished in 1953. by'DeahMukh and Varkey(90), who. precipitated the bismuth Iran the.nearly'neutral'eolution as (40)ge04.21120.

The Method es such is of little use. (11)Blemuth Molibdate. In this method, published by Miler and Van tyke Cruser(91), the bismuth waS precipitated by adding an excess of ammonium molybdate solution to the cold 'dilute nitric acid solution of thebienuth, and then neutralising the solution by the dropWise addition of' diluted aqueous atmonia. The solution was neutralised to congo-red and then one or two drops of diluted nitric acid were added to restore the lilac colodr of the indicator.' The solution was diluted'and then heated to 50 to 600. The precipitated bismuth ammonium molybdate was washed with ammonium nitrate solution, ignited and weighed as 3103441•fO03. (12)Complexthromium.Thiocvanate.' The precipitation of bismuth as bismuth chronithiocyanate by a'solation of potassiumehromithiocyanate was proposed by-Mahr(92) in 1532 as attethod of determining bismuth. A further atudy,was made by the same author(93) and was reported in 1940. The nitric acid solution should be 0.33N to IN with respect to free nitric acid. 'The reagent solution must be freshly prepared - even the solid reagent does not keep well and must be occasional recrystsilleed from alcohol. Elenents of the analytical Group II interfere -19— but those of the analytical Groups III and IV do not. (13) Complex Cobalt Saltt, Spacu and Spacu(94) have shown that bismuth can be quantitatively precipitated from a nearly neutral solution by the addition of an excess of potassium iodide solution follewed,by a solution of transrdithiocysnato- diethylenediamine cobaltic thiacysnate. The.bismuth 14013 precipitated as the corresponding tetra-iodobismuthite. The precipitate was filtered, washed with diluted precipitant, then with alcohol and ether, dried in a vacuum desiccator and weighed as the complex salty In a similar method published by Spacu and Sucio(95), the bismuth was precipitated as tri-ethylenediamine cobaltic did.tetra-iodobimuthite iodide by a solution of tri-ethylenediamine cobaltic chloride in water. The precipitate was washed and dried as in the first method.

(lA) nt th le Det t on of zany organic reagents have been used for the determination of bismuth. The greatest selectivity has probably been achieved with amines that give precipitates of salts of tetra-iodobismuthic acid. Unfortunately, these salts are often thermally unstable and it is necessary to complete the determination volumetrically. The first published method for the determination of bismuth by means of an organic compound was that of Herzog(96). This author precipitated the bismuth ,as basic acetate and ignited the precipitate to tl:e oxide for weighing. Another earlyinethod was that of Benkert end Smith(97), who precipitated., the bismuth as basic formate. These imethodev howver, are hardly examples of the use of organic reagents; the first true organic - 20 -

reagent to be used for the gravimetric determination of bismuth was

Wrogallca. Feigl and Ordelt(96) precipitated the bismuth by a concentrated solution of pyrogallol from a solution that was 0.1N with respect to free nitric acid. The complex: was filtered, washed, dried and weighed as Bi(C6H.30.3). The method is applicable in the presence of lead. A micro-method for determining biamuth as the pyrogallol complex was worked out by Strebinger and F].aschner(99). Bismuth can be determined with oxine (8-hydroxyquinoline). Berg(100) showed that it can be precipitated frcm either an acetic acid -.tartaric acid solution or from an ammoniacal tartrate solution. Halides must be absent if the acetic acid solution is used. The precipitate in filtered* washed, dried and weighed. The precipitate can either be dried at 100%. and weighed as Bi(C,H60N)3.H20, or dried at 140PC. and weighed as Bi(C H6ON)3 . According to Haynes(101), bismuth can be determined in the presence of magnesium by precipitation of the bismuth by oxine at a pH of 5.2 to 5.4 from an ammonium acetate-acetic acid solution. Berg's method has been investigated by Hecht and Reissner(102) who found that the method gave excellent results. These authors used an ammonium acetate-acetic acid-tartaric acid solution. The amnoniacal tartrate method of Berg was investigated by Mak and Krivanek (103) in 1953 and was found to give good results. The authors considered the method preferable to the acetic acid modification because halides did not interfere, and a separation from the alkali metals, the alkaline earths, arsenic III, tungsten VI, telIurimm IV and selenium IV was obtained. The year after Berg's paper on the determination of bismuth with oxine, Pinkus and Pernies(104) published a method for determining bismuth with cupferron. The bismuth was precipitated from a cold solution that was normal with respect to either hydrochloric acid or nitric acid. Hydro- chloric acid was preferable. The authors claimed that the precipitation of bismuth as the cupferron complex separated bismuth from cadmium, mercury. TI, zinc, arsenic, antimony V, aluminium, manganese, chromium, lead, nickel, cobalt, silver and magnesium. The method has been used by Ostroumov(105) and by Silverman and Shideler(17) to separate bismuth from lead. In the foil wing year, leas-Gupta(106) published a paper on the ualitative separation of bismuth from copper, cadmium and lead by precipitation of bismuth by gallic acid. Quantitative work with this reagent was undertaken by Kieft and Chandlee(107) in 1936. They precipitated the bismuth from a nitric acid solution containing 3m1. of concentrated nitric acid per 100m1. of solution. The solution was heated to 70°C., and the bismuth precipitated by the addition of solid garlic acid. The solution was stirred for one minute and then set aside to cool. The precipitate was filtered, washed with a solution containing gaIlic acid and ammonium nitrate and ignited to the oxide for weighing. The authors claimed a separation from lead, cadmium, copper, zinc, aluminium, iron, nickel, barium, calcium, sodium and potassium. Antimony, tin, mercury and silver, however, interfered. In 1938, Berg and Fahrenkamp(108) described the precipitation of bismuth by an alcoholic solution of thionalide (thioglygollic acidp.amino napthalide). This can be done from an acid solution, or from an alkaline solution containing tartrate and cyanide. From an acid solution, thionalide precipitates bismuth, antimony, arsenic, copper, gold, mercury, pall• adium, platinum, silver and tin. Frcm carbonate solutions containing tartrate, thionalide precipitates bismuth, cadmium, copper, gold, mercury and thallium. Fran carbonate solutions containing tartrate and cyanide, thionalide precipitates bismuth, antimony, gold, lead, thallium and tin. The precipitation, of bismuth from acid solutions is complicated by the fact that, in the presence of halides or sulphates, basic salts are coprecipitated and these cause low results. The precipitate is filtered, washed with water, dried at 10091C. and weighed as Bi(C121110ONS)3. In recent years, Majumdar(109, 110, 111) has applied phenylareonic acid to the determination of bismuth. The bismuth is precipitated at a pH of 5.1 to 5.3 from an acetic acid-ammonium,acetate solution. Fluorides, chlorides and phosphates must be absent as must iron, aluminium, beryllium, uranium, titanium, thorium, tin, zirconium, copper, zinc, manganese and antimony. Tin, thorium, titanium and zirconium can be precipitated first from a mineral acid solution. A separation from silver, copper, lead,

cadmium, mercury, cobalt and nickel can be obtained in the presence of cyanide. In a later paper by gajandar and Sarma(112), the bismuth was precipitated at a pH of 2 to 3 and a separation fran the alkali metals, the alkaline earths, zinc, manganese, nickel anCcobalt was obtained. Another arsonic acid* arsanilic acid, was investigated bytlasil and Pietsch(113) in 1955 and was found to precipitate bismuth from a nitric acid solution at a pH of 2 to 3. The method was of little use because of the large number of elements that were precipitated under the same conditions(335). Other methods that have been proposed for the gravimetrie deter urination of bisMuth arer (a) Precipitation of btsiuth as the tetraiodobismuthite of antipyriri.;. methYleneaMine froM an acetic acid solution(U4, 115). The precipitate can be dried at 110°O. and weighed. (o) Precipitation of bismuth from a dilute nitric acid solution by a saturated solution of picric acid(116). The method gives an excellent separation of bismuth from lead, and is suitable for the determination of small amounts of bismuth in the presence of large amounts of lead. The precipitate cannot be ignited as it is explosive. It is converted to the oxide for weighing through the basic carbonate. (c)Precipitation anti weighing as the complex iodide with hemamethylene- tetramine(117). (d)Precipitation and weighing as the bismuth salt of m captobenzthia- zole(118, 119). (e)Precipitation and weighing as the tetraiodobiemuthite of naphtho- quinoline(120). (f)Precipitation of bismuth as a basic salt of unknown composition by salicylaldoxime and ignition to the oxide for weighing(121). (g)Precipitation and weighing as biemuthyl dichromate(328). (h)Precipitation and weighing as the Reinecke salt(329). (i)Precipitation of bismuth by benzene and naphthalene selenic acids and weighing of the substituted bismuth selenates(330). (j)Precipitation and weighing as the dimeth4glyendme complex from an E.D.T.A.-cyanide solution at pH 11.(331). (k) Precipitation .of bismuth by potassium ethyl xanthate an4.weighipg as.the bismuth camplex(332)i (1) Precipitation by 0:0-diethyl phosphorodithioate frcm dilute acid.

solution and weighing as the. complex bismuth ea/t(333). (,n) Precipitation and weighing as, bismuth oxalate(334). - 25 vourmic mTHons., (1) Bismuth Pbosshate. An early paper on the volumetric determination of bismuth as phosphate was published by Ehrenfeld(122). He based his method an the gravinetric method of Staehler and Scharfehberg(3).. Ehrenfeld added an excess of standard sodium phosphate solution and back-bitrated the excess of phosphate with uranyl nitrate solution. The results varied from 9 per cent. too low to 25 per cent. too high. The author appeared to be unaware of the paper published by Muir(123) thirty years earlier in which a similar process was described. In a later paper with Indra, Ehrenfeld(124) modified his procedure and back-titrated the excess of sodium phosphate with uranyl nitrate solution, the cochineal indicator described by Repiton(125) being used. Vaseallo(126) titrated the nitric acid solution of bismuth with a standard solution of sodium phosphate and used logwood indicator papers as an external indicator. Haematin is the active compound in this indicator. KUrthy and Muller(127i) added an excess of diammonium hydrogen phosphate solution to the feebly acid bismuth solution, allowed the mixture to stand centrifuged the precipitate and determined the excess of phosphate calori- metrically. The calorimetric method used was based on the reduction of the phosphomolybdate ccmplex by hydroquinone. Bordeienu(128) used a similar process, p-bYdroXYPheA4 glycine being the reducing agent for the selective reduction of the phosphanoi.ybdatc cemplex to molybdenum blue. When chloride MB present, Uwe!) precipitated by silver nitrate before the addition of the ammonium phosphate solution, Strecker and.Ferrmann(129) added an excess of a standard solution of disedium hydrogen phosphate and determined the excess of phosphate by an argentometric method. This method. of determining phosphate vas .based on the work of Relleman(130) and also on that of Strecker and Schiffer(131). The method consisted of adding an excess of silver nitrate solution* tering off the precipitated silver phosphate, and titrating the excess of silver by the Volhard method. (2) Bismuth:a Dichromate. Muir(132), in 1876, described the direct titration of bismuth with • standard potassium dichromate solution4.silver nitrate being•used as ex., ternal indicator. Another early volumetric method based on the precipitation of bismuth as bismuthyl dichromate was that of tlbhr(133). In this method the precipitate was dissolved in sulphuric acid, an excess of ferrous sulphate•solution was added and the unreacted ferrous sulphate was back- titrated with standard potassium permanganate solution. Rupp and Schaumann(130 added an excess of standard potansium elvanate solution, diluted the solution in a standard flask, allowed the mixture to stand for ten minutes, filtered the solution and :titrated an aliquot far• chromate. The chromate was determined by diluting the aliquot with water, adding sulphuric. acid and potassium iodide and titrating the liberated iodine.mith standard sodium thiosulphate solution. More recently* Utsuni (135) used a similar method for the determination of bismuth. This author dissolved the.preeipitated bismuthyl dichmate in 3N-hydrochloric acid* added potassium iodide and titrated the iodine with.standard sodium thio.- sulphate solution. Oliverio(165) added an excess of chrcriate, filtered off the precipitate and determined the chromate content of the filtrate, or of the precipitate. laien the chromate content of the precipitate was determined it was dissolved in hYdrochltric acid. To the chromate solution was added an excess of a standard ferrous ammonium sulphate solution and the resulting ferric iron was titrated with a standard solution of titanous chloride. (3)7 smuth enmoniumilplebdate. The volumetric determination of bismuth by precipitation as bismuth

ammonium molybdate, followed by reduction and titration of the molybdenum, was proposed simultaneoucly by Riederer(137) and by Miller and Frank(138). Riederer added an excess of ammonium mcaybdate solution to the nitric acid solution of the bismuth and then neutralised the solution with aqueous ammonia, methyl orange being used as indicator. The precipitate was washed with 3 per cent. ammonium sulphate solution and dissolved in sulphuric acid .

This solution waspassed through a Jones reductor and the reduced molybdenum

was titrated with standard potassium permanganate solution. The factor

used Was an empirical one as the state of reduction of the molYbdernanwas

uncertain. Moser(139) found that Riederer a method gave good results)

haaever, the method was tedious and the permanganate solution must be standardised against pure bismuth. If the precipitate was dissolved in 2N-hydrochloric acid and the hot solution wan passed through a silver reductor, the molybdenum would be quantitative3,y reduced to Mo V. (4)Bismuth Iodat,. Buisson and Ferrer(140) stated that when an excess of potassium iodate was added to an acetic acid solution of bismuth, the normal iodate was precipitated. However, Moser(139) and Rupp and Krauss(141) both stated that the precipitate was mainly the basic iodate Bi(OH)(I03)2. This precipitate was dissolved in sulphuric acid,, potassium iodide was added and the liberated iodine was titrated with standard sodium thiosulphate solution. Alternatively.. an excess of standard potassiun iodate solution can be added,, the iodate filtered off and the excess of iodate determined in the filtrate. This was the method used recently by Castagnouk Cazaux and 1?avid(142)., A micro.volumetric method was published by Krillov(152)1 he considered the precipitate to have an indefinite composition and used an empirical factor. (5) BienuthTlhallium This indirect method of determining bismuth was proposed by Carmen and Perina(143) in 1922. The hydrochloric acid solution of the bismuth was treated with an excess of a standard potassium iodide solution. This solution was titrated with a standard solution of thallouc sulphate until yellow thallous iodide was precipitated instead of the red double bismuth thallium iodide. The precipitate was filtered off and the excess of iodide in the filtrate was determined by titration with potassium iodate solution. Thus the amount of thallium in the precipitate is known, and hence the amount of iodide combined with the thallium. The total iodide is also known and therefore the amount or iodide combined with the bismuth is known and hence the bismuth can be calculated. (6)Bismuth Sulphide.. The first volumetric method based on the precipitation of bismuth as -29 — sulphide was that of 'Ilanus(14/1) who used the general method of Mohr(145). The precipitated bismuth sulphide was digested With 'an excess' of ferric. sulphate solution and the resulting ferrous iron was titrated with • etandard potassium permanganate solution. According to lloser(139), Sane of 'the colloidal sulphur formed during the oxidation of the Sulphide was further oxidised by the Permanganate solution and the results were about four per cent. too high. Ferrichs(146) digested the precipitated bismuth sulphide with an excess of N/10 'silver nitrate solution when the reaction 60)103 + Bi2S3 3Age - 2110103)3 proceeded to completion. The excess of silver was determined by the Volhord method . (7) Bismuth Arsenate. Roedekei(147) determined bismuth by adding an excess of standard arsenate solution, filtering off the biertuth arsenate and titrating the excess of arsenate with a standard solution of uranyl acetate. According to Waits(148) and Zlos er (139 ) the method gives very poor results. Valentin(149) determined the excess of arsenate iodometrically. Kurtenacker(153) considered Valentin's method to be the best volumetric method for the determination of bismuth, but he preferred to dissolve the precipitate in hYdrochlcric acid and to determine the arsenate in the preci— pitate. (B) Reduction to 'Bismuth Metals An attempt to convert the gravimetric methods of Vanino(40) and of VTuthtlann and Mawrow(43) to a volumetric method was made by Kurtena cker and

Werner(164) in 1922 TLev issolved the bi h fist in an excess of erric-chloride eolution and the r esul tin;? fesrrcrae.iron was titrated with a standard solution of potossitsm permanganate.. Very lard results Imre ob», tattled. The authors pointed out that the precipitate contained bismuth oxide and that one per cent. of tdsmuth oxide in the precipitate mad only voice .the result of.a.mavimetrie determination 0.0 ,per cent. hicb, The same amount.of,bieluth oxide in a precipitate used for the volumetric deter• mination would.make the result 0.67per,cent. Batter results have been.obtained by. the precipitation of bismuth other metals such as copper, aluminium, magnesium and zinc. Reissaus(155) used copper to precipitate the biemuth fram'a hydrochloric.acid eolution in en atmosphere .of carbon dioxide. The emcees of copper end the precipitated bismuthwere filtered off on a pad of glass of and the resulting solution of cuprous copper was titrated with standard potassium bramate solution. rubine and Plichta(156) obtained excellmtresults with the method of Reissaue. In the presence of lead, Reissaus precipitated the.biemuth ae the oxychloride, dissolved this precipitate in hydrochloric acid and then precipitated the bismuth by displacement with ,copper turningo. In,anothermethod given in the same paper, Reissaus precipitated the bismuth from a sulphuric acid solution, by zinc powder. The precipitated bismuth _enameller dissolved.in an excess of ferric sulphate solution and the- resulting ferrous iron was titrated with a standard solution e potassium permanganate. rub and Plichta(156) reduced the bismuth to the metal in alkaline solution by aluminium foil. The precipitated bismuth:was dissolved in an ens of ferric chloride solution and the ferrous iranwas titrated with -31

standard potassium permanganate solution. Hough(157) used this method for determining bismuth in ores after the separation of bismuth, first as the sulphide and then as the hydroxide. Strecker and Herrmann(129) precipitated the biemuth by magnesium. The excess of magnesium was dissolved by boiling the solution with ammonium sulphate. The bismuth metal was filtered, washed, dissolved in ferric chloride solution and the ferrous iron was titrated by a standard potassium permanganate solution. Manus and Jilak(158,159) reduced the neutral bismuth solution with hydrazine hydrate. The precipitated bismuth was dissolved in an excess of ferric chloride solution and the ferrous iron produced was titrated with a standard potassium permanganate solution. Lespagnol et 61*(160, 161) precipitated the bismuth by the method of Vanino and Treubert(40). The precipitated bismuth was dissolved in an excess of standard iodine solution and the excess of iodine was titrated with a standard solution of sodium thiosuiphate. nirect potentiometric titration of bismuth solutions with a standard solution of titanous chloride has been described by Zinti and Rauch(162, 163, 164). The solution contained less than 0.5 per cent. volume/volume of concentrated hydrochloric acid and an excess of tartaric acid. The titration was made at the boiling point in an atmosphere of carbon dioxide. The authors claimed that iron, copper, lead, tin, cadmium and antimony did not interfere. Oliverio(165) found the method to be unsatisfactory. Similar methods had been published in which the titration was made with a standard solution of vanadyl sulphate(166) or a standard solution of chromous chloride(167, 168).

(9) Bismuth Oxychloride. The determination of the chloride content of bismuth cxychloride by the method of Volhard(169) was first proposed as a method of determining bismuth by Strecker and Herrmann(129). These authors dissolved the precipitated bismuth oxyrhloride in nitric acid, added an excess of standard silver nitrate solution and back-titrated the excess of silver with a standard ammonium thiocyanate solution. The method was also investigated by Hiltner and Gittel(170) and by Migrw(171). (10) Birmqth leek& Bipluth Olsyiodide. Strebinger and Zins(66) described a volumetric finish to their DAY- iodide method. The precipitated oxyiodide was ignited over a Teelu burner in a stream of oxygen, the iodine evolved was trapped in potassium iodide solution and titrated with standard sodium thiosulphate solution. Straub(172) decomposed the precipitated bismuth oxyiodide with caustic potash, filtered off, the precipitated bismuth hydroxide and neutralised the filtrate with hydrochloric acid. The resulting potassium iodide was oxi- diced to iodate with bromine water, the excess of bromine was boiled out and the solution was acidified. To this solution was added potassium iodide and the liberated iodine was titrated with standard sodium thiosulphate solution. Shchigol and Hal'dus(173) added an excess of standard potassium iodide solution to the bismuth solution and boiled with sodium acetate to precipitate bismuth oxviodide. The precipitate was filtered and the excess, of iodide in the filtrate was determined argentcmetrically. Reichard(174) described an acidmetric method of determining bismuth -33- oxyicdide. Fauchon and Vignoli(175) determined bismuth by running the bismuth solution into a'standard solution of potassium iodide until a permanent precipitate of the tri-iodide was formed. (11)B ituluth Selenite. Berg and Teitelbaum described a volumetric finish to their bismuth selenite mothod(176). The precipitated bismuth oelenite war dissolved in a mixture of hydrochloric and tartaric acids and an excess of potassion. iodide was added. The liberated iodine was titrated with a standard solution of sodium thiosul hate. Bucherer and Meier(177) described a direct titration of bismuth in 0.05 to 0.06 normal nitric acid« The end-point was found by filtering and testing the filtrate for bismuth. The bast results were obtained by titrating the solution at 70 to 80°C. Lead did not interfere with this method. (12)Organic Salts and Complexes. The first organic salt of bismuth to be used for the volumetric determination of bismuth was bismuth oxalate. Muir(176) described the precipitation of bismuth as oxalate, followed by treatment of the precipitate with boiling water to convert it into basic bismuth oxalate. This precipitate was dissolved in hydrochloric acid and the oxalate was titrated with a standard solution of potassium permanganate. The method was- investigated by Moser(139) and by Riederer(137) and found to be useless. In a later paper with Robbs(179), TIVir described the precipitation of bismuth as a double oxalate with potassium oxalate from an acetic acid solution. The excess of oxalate in the filtrate was titrated with potassium permanganate. A similar 31•-

method was published by Warwick and Kyle(160)4 Bismuth has been determined by precipitation by axine froze acetic.

acid-tartaric acid and am' oniacal tartrate solutions. The method was developed by Berg(1W) and investigated by Cattelaine(181). An alternative method was pub's (shed by Berg and Wurm(182) in which the bismuth was precipitated from an acid solution as the tetraiodobiemuthite of e-bydeoey- eeinolinei and the iodide content of the precipitate was determined volumetrically. The method„ however, is uneatisfactory and has been criticised by several workcrs(102, 183). The precipitate has also been titrated with 44. standard Chlorftine B solution(311)., Other methods based on the precipitation of bismuth as salts of .

tetraiodobismuthic acid have been worked out by Hayes and Chandlee(16t)

who used quinaldinet and by Beale and Chandlee(165) who used caffeine. Ethylene diamine tetra-acetic acid (8.D.T.A.) has recently been developed by Schwarzenbach and his coaelorkers(186) far the volumetric determination of many metal ione(187). This reagent has bemused to determine bismuth by several workers; a variety of conditions, auxiliary complexing agents and indicators have been used. The first published method for Use, muth was that of Pribil, Koudela and Matyska(180 who added an excess of E.D.T.A. solution and backetitrated the excess with a standard solution of iron at a pH of 3 to 5. The end-point was determined potentiometrically. Land en(169) determined bismuth by adding an excess of E.P.T.A. solution

and backetitrating the excess with a standard solution of magnesium sulphate. The solution was buffered with aqueous ammonia end borax. Erlochrome Black

T was used as indicator. In 1953, Gronkviet(190) published the first direct 35 titration of bismuth in a solution buffered with potassium acid phthalate and containing a large excess of thiourea. To this solution was added one drop of gentian violet solution and the yellow solution was titrated with E.D.T,A. until the solution was pure violet in colour. The disadvantage of the method is that six grams of thiourea were used in each titration. The next year brought a collection of more satisfactory methods* one of the most important being the method of Malat, Suk and gyba(191). These authors titrated bismuth in dilute nitric acid solution, pH 2 to 4, and introduced pyro-catechol violet as indicator. The colour change at the end-point is from blue through magenta to clear lemon yellow. Fritz (192)described a modification of Gronkvistle method and reduced the amount of thiourea required and also the number of interfering metal ions. Chang (193)published a procedure for the titration of bismuth at pH 1.5 to 2 by adding an excess of E.D.T.A. solution tared back-titrating with standard bismuth solution. Potassium iodide was the indicator, the colour change being from colourless to yellow. Two procedures have been published by Underwood (194, 195) in which the end-point is determined apectrophotometrically; these methods are not of much practical use as they offer no advantages over the method of Malat et al. and are more time-consuming. Haar and Hazen(196) describe a method in which an excess or EJI.T.A. was added to the bismuth solution and the excesswas back-titrated at pH 2.0 to 2.8 with a standard thorium nitrate solution. The indicator used was Alizarin S. The more recent publications on the B.r.T.A. method have all employed the same conditions for the titration, i.e. nitrate solution at pH 1 to pH 3 and all suffer interference frmi the sane ions, viz., iron III, mercury, thorium, chloride, phosphate, fluoride, bromide are borate. The choice of indicators now available includes pyridyl-azo-naphthol(302), pyrogallol red(303), Thoron(304), brcmogallol red(305) and xylenol orange(306). Cifka, Nalat & Suk(307) have published a modifiCation of the method Of Nalat, Suk & Ryba(191) in which mercury and iron III are reduced by. ascorbic acid in the presence of sUlPhosalicylic acid. (13) Other Methods. Other *methodsthat have been described f the volumetric determination of bismuth aret- (a)The acidmetric method ofltalaprade(197) in which bienuth and sodium thiosulphate form a complex are the acid equivalent to the bismuth is titrated to a phenolpthalein end-point with standard sodium hydroxide solution. (b) The indirect method of Nahr(198), who precipitated bismuth as hexa minochromic hexabromobialuthate and determined the wmonia content of the precipitated complex by dietillation of the ammonia and absorption in standard acid.

(c) The micro-determination of bismuth with dithizone at pH 4.0 according to the method of Reith and Van Dijk(199), (d) The precipitation titration of biemith With standard ferrocyanide solution has been described by several workers. Fujita(308) titrated at pH 146 in a nitrate-glycerol-potassium iodide medium, the iodide ion serving as indicator. Basinska and co-workers have published two methods both of which employ an acetic acid buffered solution, In the first method ferricyanide and 0-aninidine are used as indicater(309) and in the second, -37- the end-point is detectedpotentiometrienlly(310). COLORINSTRIC qmors. (1) Bismuth Iolide. This method is the oldest and the most widely used method for the calorimetric determination of bismuth. The first paper appears to have been published by Stone(200) in 1687. Since this date many papers have been published describing applications of the method and minor variations in the procedure. Accounts of these variations and applications are to be frond in the standard texts on colorimetric analysis(201, 202). Tao reviews are also available, the first is to be found in the Analyst for 1933 (45 Refs. 203) and the second is a more modern German review covering the colarimetric determination of bismuth in general(204). However, a brief discussion of the most important papers published on this method will be given. The method, which is simple in principle, consists of adding an excess of a soluble iodide to an acid solution of the bismuth salt. A reductant Is added to reduce free iodine to iodide. The yellow colour produced is moderately sensitive (sensitivity at 460mu is about 0.11g. per c4.).3 The colour intensifies with increasing iodide ion concentration up to about 1 per cent. of potassium iodide, and after this concentration is reached an excess of iodide has little effect on the colour(205). One per cent. was the concentration of potassium iodide chosen by Rowell(206); however, it would seen desirable to work with an iodide concentration of at least twice and preferably ten times this enount. Interference fran a large number of elements (i.e. suppression of the colour) is experienced with low concen" trations of potassium iodide. This effect is particularly noticeable when -39- elements such as cadmium, that also form eoluble iodide complexes, are present. The acid concentration is not critical, but hydrochloric acid should be avoided as it bleaches the colour: Acid concentrations of more than 50 per cent. volume/volume'of sulphuric acid give a weak colour with potassium iodide alone. High concentrations of nitric acid liberate free iodine and are therefore unsuitable. The most commonly used acid is sulphuric in con", centrations of about 2 per cent. volume/volume of concentrated acid(206, 207, 20(3, 209, 210). However, nitric acid has also found favour with some analysts(48,Z24, 213, P14). Fluoride in high concentrations bleaches the complex iodide colour(215, 216). The reductant most widely used is aqueOus ulphur dioxide(205, 210, 211, 212). Other roductants are stannous sulphate(217), phosphitee(218) and ascorbic acid(219). The use of a mixture of sulphur dioxide and hyPophos. phorous acid- is recomended by Haddock(211) and is satisfactory provided that the yellow complex is extracted into an organic solvent. If the aqueous solution is to be measured, the method is not satisfactory because elementary sulphur separates from the solution. An excess of sulphur dioxide Must be avoided as it produces a yellow colour with iodide ions. According to Pechard (220), thin is due to the formation of iodo—eUlphinic acid. EXtraction'of the free iodine with chloroform in the presence of glycerol as a stablising agent has been described(221). The elements that interfere in the determination arer— (a) Those that give precipitates with iodides, i.e. lead in large amounts, copper, thallium and silver,' 40

(b) Those that liberate free iodine, i.e. ferric iron and selenates.

(c) Those that give coloured camplexee with iodides, i.e. tellurium, antimony, platinum, palladium and, to a lesser extent, tin.

(d) Those whose ions are ccloured,.64, nickel, cerium and uranium. wane of these interferences can be eliminated by extraction of the yr/low colour with ,an organic solvent. Haddock(211) used a mixture oftnyl alcohol and ethyl acetate and Goto and 8uzuki(218) used iso-ankl alcohol. The absorption maximum in the ultra-violet is also less influenced by ease coloured ions.and is more sensitive than the peak in the visible region of the spectrum. The ultra-violet maldearl is at 337T.(317). A modification of the iodide method is to precipitate lead iodide in the presence of microgram amounts of . bismuth and to compare the colourof the precipitates with standards prepared in the sire ITIOXIner(2222 223, 221e,

225). (2) Bismuth Thiourep. The determination of bismuth as the ye lloe thiourea complex is the second most important method for the calorimetric determination of bismuth. Although the method is generally attributed to Mahr(227), the reaction was first described by Hofmann t:Gonder(226) in 190k, and Jilek(228) published a calorimetric method of determining. bismuth in 1920. The bismuth solution, which should be about 1N in nitric acid, is treated with a large excess of thiourea and the colour read at about 42Qmp. The method is less sensitive than the iodide method, but the sensitivity can be improved by-meaeuring the absorption peak in the ultra-violet at 322T.(317). The following ions do not interferes. chloride, .sulphate, phosphate, silver, lead, mercury, copper, arsenic, tin, aluminium, zinc, manganese, calcium, strontium, barium, magnesium, innonium, sodium and potassium. Antimorr interferes, but can be masked with fluoride. Ferric iron interferes, and must be reduced to the ferrous state by means of hydrazine eulphate(227, 229, 230). The method has been employed by numerous workers to solve special problems and a few of them may be mentioned. Tcmpeett(231) applied the method to biological samples after separation of the bismuth with diethyl-

dithiocarbanate. Leutwein(232) used the method for the determination of bismuth in ores. Woblamer and Groshelm4trysko(233) determined bismuth in lead using the thiourea method.

Nakukha(318) has investigated various substituted thioureas as reagents for bismuth.

(3) Bismuth rithizonate. Although the dithizone method is not a simple one, it has been widely used in the assay of biological samples as it enables amounts of bismuth as small as 0.9gg. to be determined.

When a solution of bismuth is shaken with a chloroform or carbon tetra. chloride solution of dithizone, tl:e bismuth reacts to form an orange-yellow complex that is soluble in the organic phase. Bismuth can be extracted from alkaline-citrate..eyanide solutions(211), although some workers have reported incomplete extraction in the presence of a barge amount of foreign nalts(199,

234). The pH of the solution has a sicnificant effect on the percentage of bismuth extracted by dithizone. Fischer(235) recommends a pH of 7 to

8, Wichmann(337) a pH of 3 to 9 and Fischer anti Leopol.di(236) a pH of 4.0. A systematic investigation of the variation of the percentage of 42 - bismuth extracted with the pH was made by Greenleaf (237). Two recent papers describing the determination of bismuth in biological canples are those of Hubbard(238) and of Laug(239). , A summary of Scene of the published methods is to be found in a recent monograph by R.J. Reynolds (240). (4) Other Method', Other methods that have been described for the colorimetric determine• tion of biamuth are:- (a)The formation of double iodides with various organic bases. Those that have been used include quinine(241, 242, 243, 244), trimethylphenA ammonia(245), tetra-acetyl annonia(246), phenazone(247, 312), 8MWroxr.i quinoline(248) and brucine(320). (b)The formation of a colloidal suspension of bismuth sulphide in acidic solutions containing gelatin(249), or gpm-arabic(250). The suspension can also be produced in alkaline solutions; the dispersing agents used include gun-arable and polivinY1 alcohol(251, 252). (c)An indirect method in which.the biemuth is precipitated as phosphate, and the phosphorus content of the precipitate is determined by one of the standard colorimetric methods(253), (d)The formation of a colloidal suspension, of elementary bismuth by redu. ction by. means of sodium stannite solution(254). (e)The formation of complex chlorides(255), bromides(256, 313) and thio- cyanates(257). (f)The fOrmation of a complex with diethyldithiocarbanate in alkaline tartrate-cyanide-E.P.T.A. solution and extraction into chloroform or carbon tetrachloride for spectrophotometric mtesurement(258, 259, 279, 314, 315). - 43

) The formation of a complex with EOM' *As which can be measured at

263.5.(260) (h) The formation of coloured complexes with organic reagents such as the red complexes with dimercaptothiobiazole(261, 262) or phenyldithio— biazolonethi ol(264) ani the yellog caeplex with dithiocarbanidohydrazide

(263). (i) The formation of molybdenum blue by the reduction of phosphomolybdic acid by bismuth pyrogallate or oximate(265), (j) The formation of the blue pyrocatechol bismuth conplex according to

Svach(316).

(k) The measurement of the ultra violet abets n of the bismuth perchlorate system in 9.5N, perchioric acid. -44..

H PS pF armAyIoN. As most of the methods of separation have already been described in the previous sections, no details of these methods are given here. N. ever, any nen reaction used solely as a method of separation is described in detail. This section is most conveniently split into subsections dealing with the individual elements. (1) Isa, This is perhaps the most important separation in, the analytical chards- try of bismuth and has been the subject of many papers. A large number of methods rely on the hydrolysis of bismuth salts to achieve the separation. Among these methods may be mentioned the precipitation of bismuth oxyiodide(67), bismuth oxychloride(58, 155, 266, 267), bismuth oxynitrate(74, 75, 76, 78, 268)„ bismuth basic fcrmate(8, 269) and bismuth oxybrornide. The last method, due to Moser andlufaxymowicz(270), employs the precipitation of bismuth oxybromide from homogeneous solution by the reaction of bromide with bromate. The precipitate is unsuitable for weighing. Numerous electrolytic separations of bismuthfram lead have been reported (22, 26, 29, 31, 34, 35, 37, 38), but these do not appear to have been widely applied. Several organic reagents and acids have been used to separate bismuth from lead. These include gallic acid(106, l07),,cupferron(17, 104), cinchonine hydrochloride and potassium iodide(271),pyrogallo1(98) and thionalide(108). Other methods that have been advocated are:- (a) Precipitation of bismuth by iron powder(9, 272). -45 -

(b)Precipitation of bismuth hydroxide in the presence of 44.T.A. and a calcium salt(278). (c)Precipitation of lead chromate from an acetic acid solution(273). (d)Precipitation of lead sulphate(2741 275$ 2764277). (e)Precipitation of bismuth phosphate(4$ 11). (f)The extraction of bismuth with a carbon tetrachloride solution of diethyl-ammonium diethyl-dithtocarbsmate in the presence of E.D.T.A. and potassium cyanide at pH 11(258$ 259$ 279, 314$ 315). (g)Precipitation of bismuth aelenite from a dilute nitric acid solution (87). A review of the separation of bienuth and lead was published recently by cest(280). (2) 922M. The hydrolysis of bismuth salts provides an easy method of separating bismuth from large amounts of copper. Use has been made of bismuth oxybromide(270), bismuth oxynitrate(75$ 78$ 268) and bismuth oxychloride(57). The precipitation of bismuth phosphate has bemused as a method of separating bienuth from copper(3$ 4$ 5$ 11$ 14). Other methods that have been recammended ares.- (a)Precipitation of basic bismuth gallate by gallic acid(106, 107). (b) Precipitation of bismuth oxinate hy8.-hydroxyquinoline(182). (c)Precipitation of bismuth sulphide in alkaline tartrate cyanide solution (10, 137, 274). (d)Precipitation of basic bismuth selenite(87). (s) Precipitation of the bismuth thionalide complex from sodium carbonate tartrate cyanide solution(108). (f)Precipitation of bismuth as a higher oxide by ammonium hydroxide and hydrogen peroxide by the method of Jannasch and Kesinsky(281). (g),Precipitation of bismuth fram a nitric acid solution by means of a mixture of pyridine and pyridine nitrate according to the method of Ostronmov(268). (h) Varioun electrolytic met 22, 30, 35). , (3) Wan. As with lead and copper, .the most important separations of bismuth from cadmium are based on the hydrolysis of various bismuth salts. Salts that have been used in,the latter separation are the oxynitrate(740 75, 78, 268), the oxychloride(58, 155, 266, 267), the oxybromide(270) and the oxyiodide(68). The precipitation of bismuth phosphate separates bismuth from minium (3,4,5,11, 14). Other methods that are available includes"-,

(a) Electrolytic nethods(358 282). (b) Precipitation of basic bismuth gallate(1060 107). (c) Precipitation of bismuth cupferrate(104).

(d) Precipitation of the cadmium iodide cosplex from a tartrate iodide solution by hydrazine hydroxide(283).

(e) Precipitation of bismuth selenite from a dilute.nitric acid solution(87) (f) Precipitation of the bismuth thionalide complex(108).

(g) Precipitation of a higher oxide of bismuth by arnoniumhydroxide and hydrogen peroxide by the method of Jannanch and Rottgen(284).

(4) MOrqpry. Possibly the best method for the separation of bismuth from mercury is — 47 —

by precipitation, of bismuth phosphate(3, 4, 6). Other published methods includes— (a) Electrolytic methcds(35)* (b) Precipitation of mercury sulphide by hydrogen sulphide tray moderately concentrated solutions of hydrochloric acid. Thus, the percentage volume/ volume of concentrated hydrochloric acid recommended by Mancha, Grassi and Schneeberger(83) was eighteen, by Schulek and Floderer(285) twenty and by Melellon(286) fifty. (c) Precipitation of bismuth as a higher oxide by a mixture of smnonift hydroxide and hydrogen peroxide by the method of Janneech and Cloedt(287). (d) Precipitation of the mixed sulphides followed by treatment by one of the following mothodss— (i)Digestion with diluted nitric acid when, according to loser(288), bismuth sulphide is dissolved. (ii)Digestion with a solution of potassium sulphide when, according to 8Ulow(289), the mercury sulphide is dissolved(290). (iii)Digestion, with a solution of sodium trithiocarbonate when, according to Rosenbladt(291), mercury sulphide is dissolved. (e) Precipitation as bismuth cupferrate(104). (f) Precipitation of bismuth thionalide complex &on a sodium carbonate tartrate cyanide aolution(lO8).

(g) Precipitation of mercury from an ammoniacal tartrate solution by hydroxylamine(292). (5) Te4uriurri. There are only three published methods for the separation of tellurium from bismuth, they are:. (a)The precipitation of bismuth oxybromide by the method of 9rukl and Vlavmowicz(293). (b)Precipitation of tellurium by sulphur dioxide from a one molar hydrochloric acid solution containing potassium iodide(294). (c) Digestion of the mixed sulphides of bisTfuth and tellurium with a solution of potassium sulphide when the tellurium is diseolved(295).

(6) Aritimony The following methods are available for the separation of bismuth from antimony:- (a)The distillation of antimony as chloride(296). (b)The precipitation of bismuth cupferrate(104),, (c)The precipitation of bismuth in the presence of tartaric acid as, the iodobismuthate of 8-hydroxyquinoline(182).

(7) Da The following methods have been published for, the separation of bismuth from tin:-

(a) The distillation of tin as bremide(296)* (b) The electrolytic deposition of bismuth in the presence of oxalic acid

(37). (c)The precipitation in the .presence of tartaric acid of the iodobienuthate of 8-hydramuinoline(182).

(d) The separation of tin as metastannic acid by evaporation of the solution with concentrated nitric acid(266).

(8) Arsenic A fairly wide choice of methods is available for the separation of =49 w bismuth and arsenic. This includes:— (a)Dietillation of arsenic as the chloride(296, 297). (b)Precipitation of the bismuth thionalide complex fray sodium carbonate tartrate cyanide solution(108). (c)Precipitation of bismuth cupferrate(104). (d)raectrolytic methods(26). (e)The precipitation of arsenic sulphide by hydrogen sulphide from comm.. trated hydrodbloric acid eolution(298). (f)The precipitation of bismuth as phosphate according to Wenger and Omer— men(299) from a nitric acid solution. (g)The precipitation of bismuth sulphide from an alkaline solution(299). (h)The digestion of the mixed sulphides with aqueous ammonia when the arsenic sulphide is dissolved(299). (9) ,siiver, The most important method for the separation of bismuth from silver is that based on the precipitation of bismuth phosphate(3, 4, 11). Other methods that are available ares.. (a) The precipitation of bismuth cupferrate(104) (0) The precipitation of the bismuth thionalide complex frees a sodium carbonate tartrate cyanide solution(108). (c)Electrolytic methods (35, 30). (d)The precipitation of basic bismuth nitrate by the method of Lowe(71). (lb) Tha The only published method for the separation of bismuth from thallium is that of Moser and Bruk1(300) who precipitated the bismuth as phosphate. All the metals alreaty considered are.precipitable by hydrogen sulphide from an acid solution. Thellium, however, is not precipitated on its own, but separations based on the une of hydrogen sulphide are unsatisfactory, because of the ease with which thaillun forms insoluble double sulphides. All the metale:to.be considered in the next part can be separated Cron bloc:WI by the precipitation of bismuth sulphide from an acid solution. The details of this method have been given in section one.

(U) Methods for the separation of bismuth tram iron include:.

(a) Precipitation of bismuth phosphate(4# 12). (b) Precipitation of biemuth gallate by elite acid(107). (c) Precipitation of bismuth eclenite after the reduction of the iron to the ferrousstate(88i 89).

(d) Precipitation of the bismuth thionalide complex after the reduction of the iron to the ferrous state with hydroxylenine sulphate(108).

(12)aallatai For the separation of bismuth from aluminium bismuth has been precipitated as phosphate(4p 12), gallate(107), selenite(88, 89), thionalide complex

(106) and cupferrate(104).

(13) Uranium The only published method for the separation of bismuth and uranium is the electrolytic method of Kommerer(301).

(14) Chromium Several published methods exist for the, determination of bismuth iron chromium. The compounds that biemuth can be precipitated as include phosphate(4), cupferrate(104), gallate(107) and thionalide cemplex(108). Electrolytic separations are also available(301). (15)Manaanese All the methods of separating bismuth from chromium, will separate bismuth from manganese. (16)Nickel. Zinc and Cobalt The methods of separating nickel,,einc and cobalt from bismuth are identical and therefore they are grouped together. The compounds that bismuth can be precipitated as include Olosphate(4, 12), cupferrate(104), gallate(107), oxychloride(266, 267) and thionalide conAmic(108). Electro- lytic separations are also available(283). (17)1Ussm9 m Numerous methods for the separation of bismuth from magnesium are available. The compounds that bismuth can be precipitated as include phosphate(14), cupferrate(104), oxychloride(266, 267), selenite(88, 89), thionalide complex(108) and oxinate(101). (18)C= i a Practically all published exavimetric methods will separate bismuth from the alkaline earth metals. The compounds that bismuth can be precipitated as include axychloride(58, 155), phosphate(14), cupferrate(104), oxinate(101), thionalide(108), gallate(107) and selenite(88, 89). Electrolytic separations are 'also available(35). (19)Sollup and.Potaseion, All the methods mentioned under the alkaline earth metals can be used to separate bismuth from sodium and potassium. In addition to these methods, 52 the precipitation of bismuth as hydromiee or carbonate serves to separate bismuth fran sodium and potassium,. -53—

S nary of the literature and selection of methods for investigation.

As the prime object of this work is to establish an umpire method of analysis that is applicable to complex materials such as ores and alloys, the chosen method must be both as accurate and as selective as is possible.

For these reasons, colorimotric methods need not be considered. None of the published volumetric methods, with the exception of the E.P.T.A. methods, is worthy of examination as each is an adaptation of a gravimetric method, awl offers no advantage over it.

Some twenty-six gravimetric methods have been published for the determination of bismuth. The most important are, the phosphate method, the electrolytic methods the oxychloride method awl the carbonate method. Of these, the phosphate and the oxychlaride methods appear to be the most promising fran the point of view of specificity.

For the separation of bismuth Iran other ions many methods have been published, but far too many of these serve only to separate bismuth fran a very limited number of ions. Also, the ions that interfere are often those that are met with in practical analysis. Sane of the canpounds reconnended for *the separation of bisiuth are not satisfactory because of the difficulty of converting, them into a suitable weighing form. This is true of such compounds as bismuth cupferrate and bismuth 8allate. The most promining methods reported in the literature appear to be the oxybranide, the oxychloride, the oxyn.itrate and the sulphide methods.

Thus, it was decided to examine the following methods:- (1) The bismuth phosphate and the bienuth oxychloride methods. - 54

(2)The volumetric methods in which S.P.T.A. is used. (3)The bismuth eulphide, the bismuth oxybromirle, the bismuth oxychloride and the bismuth oxynitrate methods of separation. Part II of the thesis hae been divided into three sections. They. are: Section (i) Examination of the stoichiometry, accuracy and selectivity of methods of determination. Section (ii) EXamination of methods of separation especially. for those elements shown to interfere in the methods of determination examined in section (i). Sqction (iii) Application of the methods examined to the analysis of ores and alloys. - 55 -

par ToI0

EXPFRIVIEllfAL WORK.

Apparatus and Tiateriale.

Weights. The set of weights used in this work were rhodium-plated brass. They were calibrated against tares, each weight being weighed by substitution. The balance used for all weighings was an Oertling fteleso- "Aatic with automatic loading of weights up to 1g. The weights were calibrated once every six months and the values obtained are shown in Appendix II. Volumetric Arparatus. All volumetric apparatus was calibrated by weighing the water contained in, or delivered by, the apparatus at a measured temperature. All volumetric glassware was kept grease free by frequent cleaning with nitric- chromic acid cleaning mixture. The method of delivering a volume from a pipette was as follows. The clean pipette was rinsed three timqs with the solution to be measured, the solution was drawn into the pipette to a level about lcm. above the calibration mark, the meniscus levelled to the mark and the pipette allowed to discharge freely while held vertically. After allowing the pipette to drain for fifteen seconds the tip of the pipette was touched against the wet side of the vessel into which the liquid was being delivered. .56—

The values for the corrections to be applied to the nominal values

of the pipettes used are given in Appendix Is as is the reproducibility of the calibrations. Glassware (e)d_Pqrcelain. All glassware was Pyrex brand and was cleaned with a mixture of chromic and sulphuric acids immediate-3,y before use. .The crucibles used were porous based Berlin ptIcelain Noil. and were obtained through Anierrnan & Co. All other procelain vessels were:Royal,

Worcester porcelain. The Crucibles were cleaned after use by tipping out the bulk of the precipitate and then sucking a suitable solvent through them. This was usually warm diluted (1+1) hydrochloric acid, The 'solvent was removed

by washing with hot distilled waters the crucible sucked dry, dried in the oven at 110°C. and ignited in the name way as the crucible plus precipitate was to be ignited. Periodically, the crucibles were cleaned by total immersion in hot

nitric-chromic acid cleaning mixture. BiemUthmetal for standard bismuth esqutiRns. The bismuth used in this work was supplied by Mining t: Chemical Products Ltd. whose analysis was Ag 22ppn. Pb llppm. Cu 3 ppm, Sb lOppm., bismuth by difference 99.9934%. No statement was made as to the non-/metallic im— purities. B9EmsntAp. Normal quality analytical reagents were used for all work. The

ammonium Phosphates nitric acid and perchloric acids used in the phosphate method were tested for chloride with silver nitrate according to the "Analar" standards method produced by the British Prug Houses Ltd., ("Analar" standards for laboratory chemicals 5th Ed (1957)). Materials that cempaled with these standards were regarded as satisfactory. The mannitol used in the phosphate method was tested for chloride by the method described (loc. cit.) for hydrated sodium sulphate. The manni. tol was also ached and the non.volatile material weighed. The limit for the residue was set at 0.02 per cent. .58.

SECTION (i)

Preparation of a. Standard Solution of Binekuth. As bismuth is very brittle, the metal was wrapped in white glazed

paper and broken by hitting; the paper with a harmer. The weight of bismuth usually taken to make one litre of standard solution was 6 to lOgrams. 7Wo or three lumps of approximately equal size were selected to make up the weight required. The bisnuth was weighed by substitution and transferred to a 500-i l. conical flask. A enall funnel was placed in the mouth of the flask and the funnel covered with a watch glees. The metal was allowed to dissolve in 50m1. of diluted (1+ 1) nitric acid and the resulting solution warmed on the water-bath to expel the bulk of the nitrous fumes. The solution was cooled, transferred to a 1-litre volumetric flask and diluted to the mark with diluted (14-99) nitric acid. The temperatUre of the solution was noted and the content of bismuth calculated to 20°C. The temperature of the solution was always noted before aliquots were taken from the solution and any correction necessary was applied. The solution was stored in a 1-litre Pyrex glass reagent bottle. gpeck.on the Ooeceptration of the StanOerd Bismuth Solution. 25-mnl. aliquots of the standard bismuth solution were evaporated to dryness on the steam-bath in a platinum dish, the last traces of nitric acid were removed by heating the dish with a small luminous Bunsen flame and the dry residue was ignited. The first two residues were ignited over a full Bunsen flame and the third in an eleetrically heated muffle furnace at 600°C. The aliquots contained 0.1682g. of bismuth. Weights of bismuth - 59 - calculated from the weights of bismuth oxide weres--* 0.1680g. 0.1683g. 0.1682g. :1San 0.1682g. The solution was therefore satisfactory and was used for the folloaing set of determinations. Petermination of Hismuth as Phosphate.' Various aliquots of the standard bismuth solution were measured into 600-Ml. beakers and the bismuth was determined by the method given by Hillebrand et al.'(Hillebrand et al./Applied Inorganic Analysis 2nd. Ed. 1953). The method is as follows:— Prepare 100m1. of a cool dilute nitric acid solution containing not more than 0.25g. of bismuth as nitrate,:free fro sulphate and chloride ions and from elements that form insoluble phosphates in dilute nitric acid solu— tion.` Add dilute ammonium hydroxide (1+ 1) slowly and with stirring until turbid, and then clear the solution by adding 9m1.' of nitric acid.• Heat to boiling, and add of a 10 per cent. solution of diammonium hydrogen phosphate in nitric acid (14.- 9), drop by drop, and very slowly at first, from a burette, as the solUtion is continuously stirred. Pilute with 30(n1. of boiling water, and let settle for one half hour at'about 800C. •Pilter through. a tared Porous-bottom crucible, transfer the precipitate, and wash with a hot two per cent. solution of ammonium nitrate containing a feu drops of nitric acid per litre. Ignite, gently at first, and then at approximately 800PC." In order to determine the amount of bismuth in the filtrates the com— plex iodide method MS selected. The method is sensitive, eimple and more selective than the test with hydrogen sulphide. The following method, based on details given in Hillebrand et al. (loc. cit. p.239.), was used:— The filtrates were diluted to 500,1. with water and 100m1. transferred to a Hessler cylinder for emparison. To this solution were added le. of 10 p©r cent. stannous chloride solution in 6N-sulphuric acid and 10m1. of 30 per cent. potassium iodide solution. After mixing, the colour was can- pared with a standard containia7 the sane concentration of reagents. The limit of detection was 0.01ng. of bismuth per 100m1. of solution) this meant that 0.O5ng. of bismuth passing into the filtrate could be detected. The following results were obtained for the determination of bismuth by the method of Hillenbrand et al. The weight of bismuth was ca1eu) ated from the volume of the standard bismuth solution, and from this the weight of bismuth phosphate was calculated. Weight of Weight of Error in Error in 12.004. BiP0 Mg.' •per cent. taken. 0.0768g. 0.0765g. - 0.3 -0.40 0.1532g. 0.1529g. - 0.3 - 0.20 0.2446g. 0.2435g. - 1.1 - 0.45 0.2446g. 0.2436g. - 1.0 - 0.41 0.2446g. 0.2437g* . 0.9 - 0.37 0.3049g. 0.3043g. - 0.6 0.20 0.3822g. 0.3810g. - 1.2 - 0.33 Mean error 0.34 per cent. The filtrates were examined for bismuth by the method described above. No bismuth was detectable. 61 netermination of Bismuth by Titration with Ethylenediamine Tetra-acetic Acid Solution. 1), T. A. Solution. Ethylenediamine tetra-acetic acid di-sodium salt dihydrate (24.) was transferred to a Winchester quart bottle and 2.5 litres of water were added, the solution was shaken• to dissolve the solid, which is not very readily soluble. Panted E.D.T.A. Solution. E.t.T.A. solution (5001.) diluted to 500m1. with water. Standard Zinc Solution. tAnalalls zinc (1.7231g.) was weighed into a 500-m1. conical flask and a small funnel was placed in the mouth of the flask. The zinc was dissolved in 20m1. of diluted (1+ 1) hydrochloric acid and the resultant solution diluted to approximately. 300m1. After. cooling, the solution was transferred to a 1-litre volumetric flask and diluted to the mark. The temperature of the solution was 20°C. Buffer. Solutign. Ammonium chloride (67.5g.) and 570m1. of concentrated ammonia solution in 1 litre. Indicator Mixturq.• Etiochrome Black T (0.2g.) ground with 100g. of sodium chloride until a fine homogeneous powder was obtained. StandarApation of the E.D.T.A Sqlution. Into three X400-ml. beakers were pipetted three separate 25-m1. aliquots of the standard zinc solutions the pipette was washed out and then used to - 62 transfer 25m1. of the E.D.T.A. solution to each beaker. To these solutions were added 200m1. of water, 51. of the buffer solution and 0.2g. of the indicator mixture and the resultant solutions were titrated with diluted E.P.T.A. solution. The colour changes were magenta to purple to pure blue at the end-point. The following results were obtained:-

1. 3.05m1 2. 3.00n1. 3. 2.95n1. Kean 3.00m1. or 0.30t0ml. of the concentrated E.P.T.A. solution. Thus, 50.00111. of the zinc solution were equivalent to 50.300ml. of E.D.T.A. solution. Therefore, the normality of the E.P.T.A. solution was 0.05209 at 19°C. or 0.05208 at 20°C. Determinatton of Bismuth. A standard solution of bismuth was prepared by dissolving 5.6702g. of pure bismuth in 20n1. of diluted (14-1) nitric acid and diluting the solution to 1 litre at 16°C. A further 30m1.'of 2N-nitric acid were used in transferring the solution to the volumetric flask. Therefore this solution contained about ilOml. of 2N-nitric acid in 1 litre. Aliquots of this solution were transferred to a 400-1ml. beaker, the solution diluted with 250m1. of water, 6 drops of a 0.1 per cent. solution of catechol violet in water were added and the solution was titrated with the standard E.P.T.A. solution. The following method of titration was used; a volume of the standard E.P.T.A. solution equal to the volume of the standard bismuth solution taken was pipetted into the beaker and the titration cempleted with the diluted E.P.T.A. solution. The end-point was very sharp, the colour changes were blue to magenta to pure yellow at the end-point. Temperature of the -63- bis-muth and, the E.P.T.A. solutions was 16°C. The following results were obtained,- Di taken.' Di found. Error in Error in 11g. per cent.

0.028436g. 0.028387g. .0.049 -0.17 0.028436g. 0.02PAP0g. .0.016 -0.06 0.056872g. 0.056851g. -0.021 .0.04 0.056872g. 0.056889g. +0.017 0.14184g. 0.14177g. -0.007 -0.005 0.14184g 0.14180g. -00004 -0.003 0•28345g., 0.2833. -0.007 .0.003 0.28345g. 0.28344g. -0.001 -0.001. Mean error -0.03 per cent. retprmination as Bismuth Oxychloride. Various aliquots of the standard bismuth solution were measured into 600.0m1. beakers and the bismuth was precipitated` by the method given in Hillebrand et al, loc. cit. p.237. The method is'as followsv- uPrepare a nitric acid solution which is free from the interfering elements that are listed above, dilute to 100111., and then add dilute ammonium hydroxide (14-2) with constant stirring and drop by drop fran a burette until a faint opalescence appears. If a precipitate Separates, redissolve it in dilute, nitric acid (14-4), and repeat the careful neutralisation with ammonium hydroxide. Add 541. of dilute hydrochloric acid (14-9), dilute the solution to 1403n1. with hot water, heat just to boiling, cover, and let stand on the steam-bath for 2 hours or preferabli, at the side of the steam-bath - 64-

overnight. Filter on paper, and wash the beaker, paper, and precipitate with two or three small portions of hot water. Pissolve the precipitate in 4m1. of dilute boiling hot hydrochloric acid (1-1-9) by dropping the acid fran a pipette around the edges of the paper, and catch the solution in the original beaker. Wash the paper with hot water, then with 1M1. of the hot dilute acid, and finally again with water. Mute with hot water to 400m1. and proceed as before. If the amount of bismuth is small, filter through a weighed Gooch crucible, wash the precipitate' with hot water and then with alcohol, dry at 1000C:, cool in a desiccator, and weigh at Bi0C1." Precipitates that had been dried at 109-1109C. lost about 0.1 per cent. in weight when dried at 140-160°C. As the weights of the precipitates were always greater than the theoretical) and constant weight was reached more quickly at temperatures of 140-160°C. this drying temperature was used for all determinations. The following results were obtained with the method of Hillebrand et al. The weight of bismuth was calculated from the volume of the standard bismuth solution,.and from this the weight of bismuth oNychloride taken was calculated. Weight of Weight of Error in Error in MOGI Bi0C1 14134. per cent. taken. found. 0.0939g. 0.0946g. + 0.7 + 0.75 0.0939g. 0.0949g. +1.0 + 1.0 0.2341g. 0.2347g. +0.6 4- 0.25 0.2341g. 0.2344g. 4- 0.3 + 0.12 0.2341g. 0.2353g. +1.2 + 0.51 -65-

0.2341g. 0.2304. +1.0 +0.42 0.2341g. 0.2354g. +1.3 4- 0.55 0.2341g. 0.2352g. +1.1 +0.47 0.4679g. 0.4712g. + 3.3 + 0.70 0.46798• 0.4722g. +4.3 + 0.92 Prean error 0.57 per cent. No bismuth could be detected In either of the filtrates from the oxychloride precipitations when the solutions were saturated with hydrogen sulphide. Bismuth less than 0.1mg. The iodide method is not reliable in the presence of chloride. The effect of ing the precipitates is shown in the following tablet— Time of Temp of Weight of Weight of Drying. drying. ppt. I ppt. II 2hr. 1400C. 0.2354g. 0.2352g. ihr • 410°C. 0.2338g. 0.2336g. Thre 410°C. 0.2338g. 0.2336g. 4.1hr. 500°C. 0.2338g. 0.2336g. +1hr. 600°C. 0.2306g. 0.2295g. Although the weights of the precipitates after ignition are nearer to the theoretical (0.2341g.), the method is not, satisfactory because the precipi— tates appear partially to decompose. This is shown by the fact that the precipitates develop brown spots after ignition at 400-500°C. The weight, however, remains constant at 400-500°C. after the initial loss has taken place. This loss could be due to the evolution of a small amount of bismuth tri— chloride. Conclusions.

The E.D.T.A. titration of bismuth is an accurate method over a wide range of bismuth concentrations. The end-point in instantaneous and very sharp.

The phosphate method'is less accurate than the E.D.T.A. titration but.. the 'precipitate is easy to filter and wash and the. precision of the method is excellent. The error is'not related to the concentration of the bismuth. The basic chloride method requires a double precipitation and takes at least twelve hours for completion. The precipitate is not so easy to handle as the'phosphate and cannot be ignited before weighing. The precision and. accuracy of -the method are poor* and vary with the concentration of the bismuth. ' AC a result of the above findingsl'it was decided to work on the phosphate and the E.NT.A. methods for the determination of the bismuth. Examination of the Bibmukh Phosphate Method. On surveying the published phosphate methods it was noticed that the nitric acid concentration used by flillemmind et al. was more then that used by Schoeller and Larnbie(15). Therefore* it was decided to try the method of Schoeller and Lambie* which is as folloast- "The filtrate (less than 100m1.) is now ready for the phosphate precipitation. It is left to cool* treated with 1 t 1 ammonia till turbid* cleared with 2m1. of.strong nitric acid* heated to boiling* and precipitated with 30m1. of 10 per cent. diemmonium phosphate solution (0.25 to 0.3g. added* drop by drop* from a burette during continuous agitation. The first portion of the precipitant is added very acidly; this results in a coarsely — 67

crystalline precipitate. 1,41en precipitation is ccrnplete, the liquid ie diluted with three'hundred millilitres of distilled water and left to settle for an hour on a hot-plate. The precipitate is collected on a tared porous porcelaincrucible and washed with hot 2 per cent. ammonium nitrate solution containing a for drops per litre of concentrated nitric acid."

Various aliquots of the standard biSmuth solution were measured into 600-ml. beakers ,and the bismuth was precipitated by thin method; the follow-

ing results were obtained. The weight, of bienuth tdcen MS calculated fran the 'volume of the standard bismuth solution, 'ant from this the weight of bismuth phosphate was calculated.

Wei.ght of weight of Favor in error in 81,04 MR% Per cent. taken. founi•• 0.0768g 0.0765g. 0.3 — 0.40 0.1532g.' 0.1522g. - 1.0 0.65 0.2446g. 0.2433g. 1.5 0.53 0.2446g.' 0.2432g. - lib - 0.57 0.2446g. .0.21129g. - 1.7 - 0.69 0.3049g. 0.3038g. 1.1 - 0.37 '0.3822g. 0.3802g. -. 2.0 - 0.52 0.3822g. 0.3803g. -. 1.9 - 0.50 0.3822g... 0.3796g. = 2.6 - 0.68 Mean error 0.56 per cent. No bismuth could be detected in the filtrates by the method described on page 59.

The results obtained with this method are much the sale as those 68 obtained with the method of Hillebrand et al., If anything, hoe:ever, the results with the method of Schoeller and LaMbie are less accurate than those obtained with the method of Hillebrand et 61.. The greater nitric acid concentration used in the method of iiillebrand et al,, is likelyto increase the selectivity of the method. For these reasons, it was decided to con- centrate on this method. As no bismuth could be detected in the filtrates, the full amount of bismuth is most likely present in the precipitates, and therefore, as the precipitates are deficient in weight too little phosphate ion is present. Therefore the bismuth phosphate precipitates were analysed Analysis of Bislut,h Phosphate Precipitates. (a) Dptermin4ion ofyposPliprus peztoxide. Method The precipitate (0.6g.) was dissolved in 20m1.. of diluted (1÷1) hydrochloric acid, in a 500-m1.. conical flask. To this solution were added 25g. of citric acid, 1007.. of magnesia 'mixture, and 1 drop of phenol-red solution (the magnesia mixture was prepared as described by Hillebrand et al, loc. cit.). The solution was neutralised with diluted (1+1) aqueous ammonia until the colour of the indicator changed to pure yellow, the solution was cooled and the neutralisation continued until the indicator Not turned purple in colour. The flask was well shaken at this stage to facili tate the crystallisation of the magnesium ammonium phosphate. After shaking, 5,114 of diluted (14-1) ammonia solution were added and the solution was diluted to 250n1. with water. The flask was stoppered and shaken periodically during the next hour. The flask was allowed to stand overnight in a - 69 - refrigerator. Next morning, the flask was well shaken and the precipitate allowed to settle. The solution was decanted through a 9-cm. No.10 WhaUnan filter paper and'the flask washed five times with anall'volumee of diluted (1+ 25) annonia solution. The precipitate was dissolved in hot 2N4iydrochloric acid and the solution collected in a 250.ml beaker. To this solution were added iml. of magnesia mixture, 0.3g. of citric acid and 1 drOp of phenol-red solution. The solution was neutralised with cooling as:before and the solution well stirred. The beaker was set aside overnight, the precipitate was filtered on a porcus-based porcelain crucible and washed with diluted (14-25) ammonia solution. The crucible wes dried in the oven and transferred to a muffle furnace at 1050°0. The precipitates were ignited to constant weight. Method II The biemUth phosphate'(0.5g.) was weighed into a 500-cnl. conical:flask and dissolved in 3C51. of concentrated hydrochloric acid. The solution was diluted to heated to 6A., and saturated with hydrogen sulphide under pressure. The solution was diluted with 100m1. of hot water and the solution again saturated with hydrogen sulphide. The final concentration of hydrochloric acid was about 2N. The solution was allowed to coca under a pressure of hydrogen sulphide.. The bismuth sulphide was filtered on a 9-cm. No.40 Whatman filter paper and washed with a solution of hydrogen sulphide in 2N...hydrochloric acid. The bismuth sulphide was dissolved in 60m1. of diluted (14-1) hydrochloric acid, the solution boiled to expel hydrogen sulphide" and the bismuth reprecipitated as bismuth sulphide. The combined filtrates were evaporated almost to dryness, 50m1. of water were added and the solution was tested for bismuth with hydrogen sulphide. No tianuth was found. The solution was boiled to expel hydrogen sulphide, 1Ceil. of concentrated hydrochloric acid and a few drops of bromine water were added and the solution again boiled. To this solution Were added 100m1. of magnesia mixture and 3. drop of phenol-red indicator solution. The solution was neutralised with diluted (1+ 1) aqueous ammonia until the colour of the indicator changed to yellow, the solution was then cooled and the neutralisation continued until the colour of the indicator just changed to purple. The solution was well stirred and then 5m1. mere of diluted (14-1) ammonia solution were added. The total volunewas,made up to 250m1.14ithwater and the beater set aside overnight twat morning the precipitate was filtered on a 9-on, No.40 Whatman filter paper and washed with diluted aqueous ammonia (14-25). The precipitate was dissolved in hot 2N-hydrochloric acid and reprecipitated after the addition of Iml. of magnesia mixture. The determination was completed as already described under method I. (b)tpLeg t r . The bianuth sulphide precipitate and paper were boiled with 2(l. of diluted (1+ 1) nitric acid, and, when the paper was completely pulped, the. cooled solution was filtered. The filter paper was washed with 2N-nitric acid and then with water. The bismuth in the combined filtrates was precipitated as the basic carbonate by ammonium carbonate solution.

Ammonium carbonate solution was added to the cold bismuth solution until it was alkaline to meth 1 red indicator. The solution was heated to boil. ing and the beaker then set aside on the steam-bath for two hours. The precipitate was filtered on a 9-cm, No.40 Whatman filter paper, dissolved in 2N-nitric acid and reprecipitated as the basic carbonate. The second precipitate was dissolved in 2N-nitric acid and the solution transferred to a platinum dish and the bismuth determined as described on page 58 under "Check on the Concentration of the Standard Bismuth Solution'.

The phosphate precipitates from bothinethods were dissolved in hot 2N-sulphuric acid and tested for bismuth by the complex iodide method. No bismuth could be detected in either precipitate. The following results were Obtained. Each result is themen of two results which agreed to within one part in a thousand. Constituent . Theoretical Found Found Method I Method YI

111203 76.65 per cent. 77.25 per cent P205 23,35 per cent. 22.85 per cent. 22.84 per cent. Total 100.00 per cent. 100.10 per cent. peterminatpn of the epee 9f ;the law rhospherys Pentorideicontents of the Precinitate,. The above experiments confirmed that the reason for the low results

obtained was a deficiency of phosphate in the precipitate. This could be due to one of the following effects, or a combination of any of thews

(a) Loss of P205 during washing or ignition.

(b) Precipitation of basic bismuth phosphate. - 72 -

(c) Coprecipitation of basic bismuth nitrate. Teets were now carried out to decide which of these effects was responsible for the low results obtained. A freshly precipitated bismuth phosphate was washed in the normal way and then with a further 1001. of wash liquid. This wash liquid was evaporated to dryness and the residue was dissolved in 10m1. of diluted (1+ 9) nitric acid. To another lOnl. of the same nitric acid were added 2g. of ammonium nitrate and 0.1mg. of P205 as ammonium phosphate. To each solution was added 5M1. of ammonium molybdate reagent (prepared according to Ilillebrand et al. loc. cit.) and the mixtures heated to about 60°C. No phosphate was detectable in the filtrate from the bismuth phosphate but the standard clearly showed the presence of phosphate. Thus, it was concluded that the Ices of phosphorus pentoxide was not due to hydrolysis during washing. As the bismuth phosphate precipitates rapidly reach constant weight and show no gradual loss in weight on ignition, it was concluded that the loss of phosphorus pentoxide did not occur during ignition. The existence of basic bismuth phosphate appears to be somewhat doubtful. A discussion of the evidence for its existence is presented in llellorle Com- prehensive Treatise on Inorganic Chemistry in the chapter on bismuth p.711. If the log results obtained were due to the formation of basic bieruth phos. phate, the amount of basic phosphate required to lower the results by the amount found would be three to five per cent. of the basic salt. This amount might be detectable by an X-ray Oefraction powder photograph. No evidence could be found for the presence of a basic phosphate when the X-ray defraction photographs of the precipitateswere ermined. Thus, it wan concluded that the low results were most likely to be caused by the coprecipitation of basic bismuth nitrate. The fact that the coprecipitation of basic bismuth chloride and basic bismuth sulphate is reported in the literature seemed to support thin visa. Therefore, the umignited precipitates from the method of Hi llebrand et al. were washed with water, alcohol and ether and allowed to dry on filter papers, and then =mined for nitrate by the following methods:- Method The blemuth phosphate (100 to 200,g.) wan mixedwith 25ml. of water in a 500wmli conical flask and the liquid heated to boiling. To the boiling suspension were added 25m1. of concentrated sulphuric acid, and the solution titrated Immediately with a standard solution of indigo in dilute sulphuric acid. The indigo was standardised against pure potassium nitrate that had been dried at 11CPC. In the presence of nitrate the indigo changes in colour fron blue to pale yellow, the end-point is shown b:r the development of a permanent blue or green colour in the solution. MOW I; A anal], quantity of the precipitate (1 to 10mg.) was weighed onto a spot tile, one drop of 2N-hydrochloric acid wan added and the mixture stirred with a draon out glass rod until the precipitate had dissolved. To this drop was added 10 drops of the reagent (0.5g. of diphenylamine dissolved in 100i1. of concentrated sulphuric acid and diluted with 20m1. of water), the mixture stirred, and the blue colour allowed to develop for 1 minute. The sensitivity of the method ie about 0.2 micromens of nitrogen in one drop. -74-

When the reagent was added to the dissolved bismuth phosphates a white precipitate was formed, this changed the tint of the colour produced and made comparison with the standard spots difficult. This was overcone by adding a similar amount of ignited bismuth phosphate to the standards. The amount of nitrogen estimated by method II wan 0.1 per cent. and by method I was 0.05 per cent. 'Method I probably gives the more reliable figure) duplicate analysis showed reasonable agreement i.e. 0,048 per cent. and 0.052 per cent. However, method II is only semi.mquantitative. Assuming the figure 0.05 per cent. nitrogen for the nitrogen content or the precipitates, the foiloaing figures can be calculated:- The precipitate contained 1,03 per cent of BiONO3. This would yield 0.84 per cent. of bismuth oxide on ignition. The precipitate exanined contained 25 per cent, of water, no the above figure for the dry precipitate would be 1,05 per cent. of bismuth oxide. This is equivalent to a deficiency in weight of 0.37 per cent. of the precipitate. Therefore, the law results obtained by the methods of Hillebrand et al are due to the coprecipitation of basic bismuth nitrate, which yields bismuth oxide on ignition.

The most obvious method of reducing the coprecipitation of a basic salt in to increase the concentration of acid present during precipitation. There'

fore, the following determinations were carried out using the method of Hille- brand et al. except that the nitric acid added prior to precipitation was

increased to the amounts ehown in the following table. Weight of bismuth taken was 0.1682g

-75-

Volume of Weight of Bi in the kNO3 Bi found. filtrate. 7M1. 0.1678g. 0.05mg. 12ml. 0.1677g. 0.5g. 17%10 0.1667g. about Img. Increasing the nitric acid concentration appears to decrease the co— precipitation of basic bismuth nitrate, but this is offset by the increase in the solubility of the bismuth phosphate. The solubility of the bismuth phosphate will be reduced by increasing the ammonium phosphate concentration. Therefore, the fallowing determinations were carried out using the method of Hillebrand et al. with the volumes of nitric acid and ammonium phosphate solution shown in the table. Weight of bismuth taken was 0.1682g. Volume of Volume of Weight of mNo3 (NH4)2HPO4 Bi found. 7m1. 60n1. 0.1679g. 120n1. 0.1678g. 10n1. lag- • 0.1685g. lCml. 0.1666g. 10m1. t 1. 0.16846. 20m1. X2001. 0.1688g.. No bismuth could be detected in 'the filtrates. The added volumes 'of ammonium phosphate that are underlined indicate,that the ammonium phosphate solution was made up in water instead of in diluted (14-9) nitric acid. The precipitates obtained, especially in the last four de to were remarkably hygroscopic, this was not so with the precipitates obtained by the other procedures. It may be that the correct, or nearly correct, - 76 - results obtained by these procedures are due to the cancellation of errors, the increase in weight being due to the coprecipitation of zranonittn phosphate. In a paper on the organic complexes of bismuth with various h3rdrcay— canpounds, Vanino Gni 1'.art1(336) described the preparation of sire bismuth phosphate from nitric acid solutions containing rnarmitol. It therefore seemed poseible that the coprecipitation of basic bianuth nitrate could be prevented by the addition of mannitol to the solution. Various aliquots of the standard bismuth solution were measured into 600-ml. beakers and the foliating determinations were carried out by the method of llillebrand et el. except that after the addition of 5711. of concentrated nitric acid 1g. of mannitol was added. The weight of bismuth taken was calculated from the volume of the standard bimuth solution, and from this the weight of bismuth phosphate was calculated.

Weight of Weight of Error in Error in per cent. B11304 taken. fours.

0.0768g. 0.0768g. 0.0 0.00 0.1532 0.1532g. 0.0 0.00 0.2446g. 0.2446g* 0.0 0.00 0.2446g. 0.2447g. + 0.1 + 0.04

0.2446g. 0.2448g. + 0.2 0.08 0.3049g. 0.3047g- - 0.2 -0.07 0.3049g. 0.3048g. - 0.1 -0.03. 0.3822g. 0.3822g. 0.0 0.00 0.3822g. 0.3821g. — 0.1 — 0.02

0.3822g. 0.3820g. —0.2 — 0.05 tSean error — 0.005 per cent. The results obtained with this rlodification of the method of Hiflebrand et al. are much closer to the theoretical than those obtained by the original. method. This could be due either to a reduction in the anount of coprecipi— tated oxynitrate or to the eoprecipitation of some other material caused by the presence of the mannitol. To decide which of these. factors was opera— tive the precipitates frqm the mannitol method were examined for nitrate by method II given on page 70 and the bismuth and phosphorus contents were determined 07 the methods given on pages 68.71. The nitrogen content of the precipitates was found to be 0.005 per cent. The effect of this mount of nitrogen would be to reduce the weiltt after ignition by about one part in three thousand. The results for the analysis of the precipitates are given belga. Each result is the mean of two determinationss.the results of which agreed to one part in a thousand. Constituent. Theoretical. Found Method I Found Method II

Bi 03 76.65 per cent. 76.70 per cent. 76.70 per cent.

•P2 05' 23.35 per cent. 23.26 per cent. 23.24 per cent. 'rote], 100.00 per cent. 99.96 per cent. 99.94 per cent. The above results show that in the presence of mannitol the precipitated bismuth phosphate has a very small nitrogen content and a composition close to the theoretical. , As the phosphorus determinations involve the double precipitation of magnesian ammonium phosphates slightly log results are to be expected. The above results combined with the figures given in the table on page 76 indicate that the monsitol modification of the method of Hillebrand et al. is a satisfactory method of determining bismuth. The method as it was being used appeared to be very trustworthy, but each step of the method Was now examined to see that all the variables could be controlled and to find out what degree of control was necessary. Check or{ the Standard 3isiuth Solution and the Thermal Stability of Binmuth Oxide. Just to ensure that the bisiuth solution was correct the composition VW checked by the following method. An aliquot of the bismuth solution-was evaporated to dryness on the water-bath in a platinum dish, the last traces of free nitric acid were removed by rotating the dishy held in a pair of platinum tipped tongs, over a small luminous Bunsen flame. The dish was then transferred to the mouth of the muffle furnace and the bulk of the nitrogen oxides were driven off. The dish was then moved into the furnace and ignited at, the temperatures shown in the table for a period of 15 minutes. Temperature First wt. Second wt. of ignition. of Bi203. of Bi205. (1) 600°C. 0.2930. 0.2929g. (1) 700PC. 0.2929g. 0.2929g. (1)1000 0d. 0.2919g. 0.2919g.

(2) 600°C. 0.2942g. 0.2930g. (2) 700°C. 0.2930g. 0.2950g. (2) 1000°C. 0.2930g. 0.2930g.

(3) 6000c. 0.2930g. 0.2930g. (3) ?ed. 0.2929;. 0.2930g. (3) 1000°C. 0.2929g. 0.2930g. The weight of bismuth oxide calculated from the weight of bismuth taken was 0.2930g. Thus the standard bismuth solution is satisfactory. Although bismuth oxide is thermally stable up to temperatures of 100000., heating to temperatures above 700°C. should be avoided. Above this temperature bismuth oxide melts and when resolidifics on cooling the film cracks. This may caws mechanical ejection of *mall pieces of oxide. The loss in weight in the first set of determinations is attri— buted to this cause. Molten bizenith oxide also attacks poreelein and silica crucibles. Atiueteent of the Acidity for Precipitation. In the initial neutralisation of the solution it was eometimes difficult to decide when the first precipitate formed* so the following tests on re— producibiLity ware carried out. Three identical aliquots of a bionuth nitrate solution were ncutralieed in the normal way with diluted (1+ 1) ammonia so/ution* added from a burette. The follcwim volumes were required to produce a turbidity 1.(>11.* 0.7 1. and 1.2ml. and the following additional volumes to produce a definite precipitate, 0.6m1.* 1.3ml. and 0.5m1 When le,. of mannitol wan added before the addition of the Orrnonia solution* the followirg volumes of ammonia solution were required to produce a precipitate (no turbidity is produced in the presence of marnitol) 2.eml. and

thi • It is therefore better to add the mannitol to the solution first and then to neutralise the solution with aqueous ammonia. Titration of the concentrated nitric acid with standard i4/1 sodium hydroxide shared that the acid was 16.1N. Titration of the diluted (1+1) 80

aqueaus ammonia-shomd that the anmonia colution was 6. S=L Thus, the

additional quantity of acid required if themannitol is added prior to neutralisation is about lml. of concentrated nitric acid. As the concentration of concentrated nitric acid is likely to vary, the amount of nitric acid was fixed at 10n1. of 10N acid (the mannitol being added before neutralisation). Amnust of BA,m4th that can, be Ilqersirrei by the Ilannitol Method. In the folloaing determinations, pieces of pure bismuth were weighed into 600-ml. beakers, dissolved in 10m1. of diluted (1+1) nitric acid and the bismuth determined by the imannitol method. Weight of Calculated Weight of Ili taken. weight of 131204 1311104 . found. 0.2023g. 0.2942g. 0.2942g. 0.3290g. 0.4785g. 0.4763g. 0.4266g. 0.6204g. 0.6180g. 0.5199g. 0.7562g. 0.7531g. 0.5524g. 0.8034g. 0.8000g. In the last determination the nannitol was increased to 2.5g. It appears that the correct result is only obtained when precipitation of the phosphate does not begin until part of the precipitant has been added. If the first drop of the precipitant causes a permanent precipitate to form the results are always lair. When the easposition of the precipitant was altered to 5 per cent. of diammonium hydrogen phosphate and 10 per cent. of nitric acid precipitation was delayed even when 503,g. of bienuth were present. The folloaing determinations were made with 60m1. of the modified precipitant. —el—

Weight of Calculated wt. Wt. of BiPO4 Bi taken. of BiPO4. found.

0.4649g. 0.70528. 0.7039g. 0.5148g. 0.7462g. 0.7477g. 0.5028g. 0.7311g. 0.7301g. The amount of bismuth in the filtrates was about 0.2mg, The loss of bismuth in the filtrate due to the increased nitric acid concentration prevents this modification from being used.

In the two following determinations the whole determination was carried out on twice the normal scale except that the final dilution was the same i.e. to approximately 45Ctl. Weight of Calculated wt. Wt. of BiPO4 Bi taken. of BiPO4. found. 0.4046g• 0.58e4g. 0.5880g. 0.5062g. 0.7362g. 0.7357g. The' bismuth phosphate mannital method of determining bismuth is only satisfactory providing the amount of bismuth does not exceed 250mg., it is probably safer to place the upper limit at 200mg. of bismuth. It was thought that it might be possible to increase the amount of bismuth that could be determined by using a stronger complexing reagent.

The use of tartaric and citric acid was investigated. When 1g. of tartaric acid was used in place of the mannitol the precipitation of the bismuth was incomplete (approx stately 0.3mg. of bisn,:uthwas founi in the filtrate) and the result was lei. This appears to be due not only to the incomplete' precipitation of the bismuth but also to the coprecipitation of bismuth tartrate, which yields bismuth oxide on ignition. With 1g. of citric acid the -82- precipitate eces not form until about 25ml. of the aTmonium phosphate solution have been added and then it separates as a fine crystalline precipitate which adheres tenaciously to the sides of the beaker. A qualitative test shaaed that a large amount of the bismuth had remained in solution. The stability of the complexes formed with citric and tartaric acid appears to decrease rapidly between 90°C. and 100°C. At te-greaturee below 90PC., no precipitation takes place in the presence of citric or tartaric acid unless the solution is allowed to stand for a long time. Citric or tartaric acid cannot therefore replace mannitol in the biemuth phosphate determination. Thermal Stability of Bismuth Phesnylata, Aliquots of the standard bismuth solution were measured into a 600-ml. beaker and the bismuth phosphate was precipitated by the mannitol method. The precipitate was filtered on a porous-Wed porcelain crucible and ignited in an electric muffle furnace. The might of bismuth phosphate calculated from the might of bismuth taken was 0.2731g. The colour of the precipitates became pale vellae after ignition at 900°C. and pale yellow with dark brown spots after ignition at 1000°C. The crucibles aimed no deterioration after ignition at 100000. The weights obtained at various temperatures are sham in the following table:- Weight of Temperature Time of BiP0 of ignition. 0.2737g. 500°C. 0.5 hour 0.2732g. 5003C. 0.5 hour 0.2732g. 5000C. 1.0 hour 0.2732g. 600°C. 1.0 hour 0.2730g. elec. 1.0 hour .133.

0.2732g. COOPC. 1.0 hour 0.2731g. 90000. 1.0 hour 0.2728g. 10000C. 1.0 hour

500oc. 0.2737g. 0.5 hour 0.2733g. 5000(1. 0.5 hour 0.2733g. 5000C. 1.0 hour 0.2729g. 600°0. 1.0 hour 0.2725g. 8000C. 1.0 hour 9 0.2729g 600 C. 1.0 hour 0.2728g. 9009C. 1.0 hour 0.2726g. 100090. 1,0 hour One determination was carried out and the bismuth phosphate was washed with alcohol and ether, sucked dry at the pump and weighed after standing for ten minutes in the balance case. .The weight of the precipitate was. 0.2637g., after drying at 110°0. it was 0.2779g.. and after ignition at 5000C, it was 0.2729g. This does not correspond with a definite hydrate (cf. L. Vanino loc. cit. who etates that the precipitate is 3iPO4.31420). It was concluded that the best temperature for the ignition of bismuth phosphate was at 7000C., although satisfactory results could be obtained in the range 500-6000C. Prying of the precipitate at a low temperature is not satisfactory. Temperatwee_of th9 Solution bef9re Precipitation. When the amount of bianuth being precipitated ms /Teeter than about 150ng. it was noticed that the volume of precipitant that had to be added before a precipitate formed varied considerably from one determination to - 84 -

the next. When the amount of bismuth is small the effect is not so noticeable as the volume of precipitant that is added before the precipitate starts to form is much larger. The only variable not being carefully controlled was the temperature of the solution before precipitation. The following tests wore made with 175mg. of bismuth. Temp. before Temp. after ppt. Vol. of precipitant precipitation. started to form. added before ppt. formed. 100°C. 85°C. 0.2ml. 90°c. 80°C. 0.inl. 80°C. 73°C. o.6mi. 700c. 75°C. 1.2m1. 70°C. 67°C. 1.2m1. 60°C. 56°C. This effect is similar to that observed in the presence of citric or tartaric acid (see pages 81-82). As it is desirable for someprecipitant to be added before precipita-; tion begins (see page SO) the temperature of the solution before precipitation was adjusted to about 70°C. The method was now working satisfactorily with pure solutions of bismuth nitrate. The final method is given below:- (a) ReaRentl. Ammonium Phosphate Solution. Dissolve 50g. of diammonium hydrogen phosphate in a mixture of 300m1. of water and 5011. of nitric acid. Tiilute the solution to 50011. with water and allow the solution to stand for about 24 hours. Filter the solution 85 - through a 9-cm. 1Ioik0 Whatean filter paper into 0 500-ml. Pyrex reagent bottle. The solution is allowed to stand before filtration as sometimes a email amount of precipitate separates fro the freshly prepared solution. Mannitol Solution. Dissolve 5g. of mannitol in about 30m1. of warm water and dilute to 50m1. Filter the solution through a 9-cm. No.40 Whatman filter paper. The solution should be freshly prepared. 10N-Nitric Apiei. The concentrated acid is boiled to expel the oxides of nitrogen, cooled and 1m1. titrated with Nil sodium hydroxide solution. The calculated volume of this acid is diluted with water to give the 10N-nitric acid. (b) Method. To the cold nitric acid solution contained in a 600-ml. beaker, add lg. of mannitol dissolved in 10m1. of water. Neutralise the solution by the dropwine addition of diluted (14-1) aqueous ammonia until the first permanent precipitate is formed. Clear the solution by the addition of 10m1. of 10N-nitric acid and adjust the volume to 100m1. with water. Heat the solution to about 7090. Start stirring the solution and then add very slowly, drop by drop, from a burette 551. of ammonium phosphate solution. Continue stirring the solution and add a further 25m1. of the precipitant; the rate of addition of this 25ml. can be greater than for the first 5i1. Heat the solution to boiling and stir continuously to crystallise the precipitate and prevent bUmping. Dilute the stirred solution gradually with 300m1. of hot water and again heat to boiling. Set the beaker aside on the hot-plate for 1 hour. The solution should be stirred occasionally and the temperature kept near the boiling point during the digestion of the precipitate. Filter the precipitate on a porous-based porcelain crucible and wash with hot diluted (1+ 999) nitric acid. Pry the precipitate and crucible in the oven at 110°C. and ignite at 700°C. 'Weigh as 11PO4. The factor to convert the weight of bismuth phosphate to the weight of biemuth is 0.68755. Petermination of t3ismuth in the Presence of some Other Ions. The first typo of interference to be examined was the effect of small amounts of foreign anions such as might be introduced during the separations necessary in the analysis of complex materials. Chloride. A standard solution of chloride as prepared from sodium chloride (1.65g. NaCl in 100m1. of water. 1ml. is equivalent to 1() g. of chloride). Even in the presence of only 2mg.- of chloride* it was impossible to obtain a clear solution after the neutralisation with aqueous ammonia. Bromide. A standard solution of brcmide was prepared from pUre potassiuM bromide (1.49g. of potassium bromide in 100m1. of water. l'nl. is equivalent to 10mg. of bromide). Aliquots of this solution were. added to a standard weight of pure bismuth and the bismuth determined by the mannitel method. The follow ing results wore obtained. The weight of bismuth taken was calculated from the vobrne of the standard bismuth solution* and from this the weight of bismuth phosphate was calculated. Weight of Weight of Weight of 011204 ar 3120, taken. taken. found. 0.2909g. Nil. 0.2909g. 0.2909g. Nil. A0.2908g. 0.2909g. 5mg. , 0.2908g. 0.2909g. 5ng. 0.2908g. 0.2909g. 10mg. 0.2909g. 0.2909g. 10mg. 0.2908g. No bismuth was detectable in the filtrates. With. 20mg. of braiide present it was impossible to get a clear solution after the neutralisation with aqueous annonia. AIL:bate. The weights of sulphate used were ,obtained by weighing ammonium sul— phate and adding this to the bismuth solution .before neutralisation. The bismuth as precipitated by the mennitol method. The weight of bismuth taken was calculated from the volume of the standard bismuth solution, and from this the weight of bismuth phosphate was calculated. Weight of Weight of, Weight of BAP% annonium BiPO4 take4 sulphate, found. 0.3822g. 0.5g. 0.383341. 0.3822g. 1.0g. 0.3835g. 0.3810g. 0.2g. 0,3815g. 0.3810g. 0.2g. 0.3813g. 0.3610g. 0.1g. 0.3811g. The precipitations seemed normal even in the presence of 1.0g. of ammonium sulphate. No bismuth was detectable in the filtrate. Perr. rate. A measured volume of the standard bismuth solution was evaporated to fumes udth 10ml. of concentrated perchioric acid (70 per cent.), allowed to cool, transferred to a 600-ml. beaker and the bismuth precipitated by the mannitol method. The weight of bismuth phosphate calculated tram the weight of bismuth taken was 0.2732g., the weights of bismuth phosphate found were 0.2731g. and 0.2731g. With no mannitol added, the weight found wan 0.2721g. Conclusions. The solution for the precipitation of bismuth by the mannitol method can contain large amounts of perchloric acid, but should contain no chloride and not more than 10mg. of bromide ion or 50,g. of sulphate ion. The second type of interference to be examined was the effect of other metal ions. A solution of each element was prepared and is described under the appropriate element. The volumes of the bismuth and the other metal volutions were measured frcm a burette. After adjustment of the total volume and the acidity, the bismuth was precipitated by the mannitol method. The precipitates were filtered on a 9.em. No.31 Whatman filter paper and washed with hot diluted (14-999) nitric acid. The precipitates were then examined for the presence of the other element by the Methods described in the following sections.

A 0.1N solution of silver nitrate was used no the standard silver solu— tion. The bismuth phosphate was examined for silver by dissolving the

89 -

precipitates in 5m1. of diluted (14-1) hydrochloric acid, the paper was then well washed with diluted (14-99) hydrochloric acid and finally with three 1-ml. portions, of 4N-ammonia solution. The combined solutions and washitrawere diluted to 5aml. in a Tessler cylinder and 0.1g.- of potassium bromide was added. 'The turbidity was compared with standards prepared from pure bismilth phosphate and silver ,nitrate solution. The solutions were allyded to stand for ten minutes before the Comparison. was made. The limit of detection was 0.1mg. of silver in 500., of solution. The following re.. sults were obtained:- eight of Weight of Wt. of Ag in tai taken. Ag taken. precipitate. 250m g. 20mge Less than 0.1mg. 25011g. 5C rug. 0.2mg 25Dm. 500mg. 1.0mg Thallium. A stock solution of thallium was prepared by dissolving 2.60g. of thaIlous nitrate in 200n1. of water. The thallium nitrate was dried for

1 hour at 100°C. and allowed to cool in a desiccator. The thallium solution contained about 10, g. per ml. of thallium. The bismuth precipitates were tested for thallium by the follaaing method. The precipitates were dissolved in diluted (1+ 1) hydrochloric

acid and the solution diluted to 100m1. in a volumetric flank with acid of the same concentration. A standard solution of thallium was prepared that contained 1 microgram of thellium per ml. in diluted (14-1) hydrochloric acid. A solution of pure bismuth phosphate in diluted (1+1) hydrochloric acid was prepared by dissolving 3801g. of the bismuth salt in 100m1. of the acid. Suitable quantities of these solutions were mixed in a test tube and diluted to 5m1. with diluted (1+1) hydrochloric acid. Aliquots of the test solution were transferred to test tubes and the total volume made up to ,nle with diluted (it].) hydrochloric acid. The standards and the test solutions were then treated by the following method. To the solution was added sufficient bromine water to produce a permanent yellcmreolour (thin oxidieee thal. lcus salts to thallic salts) and then sufficient solid nulphos4icylic acid to decolorise the solution (this reduces excess /free bromine to bromide ion with the formation of bromo-sulphosalicYlic acid). To this solutionumre added 5 drops of 0,05 per cent. rhodamine B in concentrated hydrochloric acid and 2m1. of benzene, the mixture was shaken, the layers were allowed to separate and the benzene layer was examined. In the presence of thallium, the benzene layer weds pink in colour when viewed in daylight; under the ultra-4iolet lamp the benzene layer showed a strong yellow fluorescence. The limit of detection for thallium was 0.05 microgram in 5m1. under the ultra-violet lamp(338). The following results were obtained.

Weight of Weight of Wt. of Tl in Bi taken. T1 taken. precipitate. 25thg. 501g. 0.1mg. 250 g. 250mg. Mug* 25Cmg. 50Dng. 1.0ng• laid* A stock solution of lead was prepared by dissolving 16g. of pure lead nitrate in a mixture of 10m1. of concentrated nitric acid and 990A. of water. This solution contained about 10 me. of lead per ml. As it was difficult to find a suitable method for the reliable estimation of the. coprecipitated lead, it was decided to filter and weigh the bismuth phosphate in the normal way before estimating the lead. The weight of bismuth taken was 0.2483g. The following results were obtained:- Weight of Calculated Wt. of BiP0 Pb taken. Wt. of HiPO4. found. 4 Nil 0.3613g. 0.3611g. Nil 0.3613g. 0.3612g. Img. 0.3613g. 0.3619g. 2mg. 0.3613g. 0.3627g. 5mg. 0.3613g. 0.3655g- 50mg. 0.3613g. 0.3810g. 25Chg. 0.3613g. 0.4075g. 500mg. 0.3613g. 0.4149e. The amount of lead in.the precipitates when ]mg., 2mg. and 5ng. of lead were taken was approximately 0.5mg., 0.9mg. and 3.1mg., respectively. (Calculated assuming the lead to be present as Pb (PO4)2.). The precipitates obtained in the presence of large'amounts of lead were pink in colour after ignition and a qualitative test showed that major amounts of lead were present. The following procedure was used to eve an idea of the quantity of lead present in the precipitates. The precipitate was transferred to a small test tube and 20 drops of 3N-caustic soda solution were added. The solution was boiled for 1 to 2 minutes and the solid allowed to settle. One drop of the supernatant liquid was transferred to a drop-reaction paper and one drop of bromine water was added followed by one drop of aqueous ammonia. The paper was then warmed over a small micro-flame to expel the excess of ammonia. One drop of benzidine solution was added (5mg. of

-92—

benzidine dissolved in Imi. of glacial acetic acid and diluted to 1Cml. with water. ' This solution must be freshly prepared.). and, in the presence of lead, a blue fleck developed. The sensitivity of the test is about 0.2mg. of lead in the total precipitate. (See F. Feigli 'Spot Tests, In-, organic Applications' page 68 and 389). tlercurY. A stock solution of mercury was Prepared by dissolVing 5.00g. of AnalaR mercury in 25m1. of diluted (1+ 1) nitric acid and diluting the solution to 50Cm1. with water. The mercury in the precipitates was estimated by dissolving then in 50m1, of diluted (14-1) hydrochloric acid and saturating the cold solution with hydrogen sulphide. With 0.11g. of mercury present, the solution turned yellow; with 0.2m g.„ 0.,ftg. and °Jong. of mercury present, stronger yellow colours were obtained. With 0.5mg. of mercury, a yellow precipitate separated almost immediately. tihen lore than Ling. of mercury were present, the precipitate quickly turned black. The following results were obtained. Weight of Weight of Wt. of Hg in 8i taken. Hg taken. precipitate. 250mg. 2mg. Less than 0.1mg. 250ng. 2Ong. Between 0.5 and 1.0ng. Copper. A stock solution of copper was prepared by dissolving 38g. of Cu(NO3)2.3H20 in a mixture of 10m1. of concentrated nitric acid and 990m1. of water. This solution contained approximately 10mg, of copper per ml. The copper in the precipitates was estimated by dissolving the biemuth phosphate in 5n1. of warm 2N-hydrochloric acid. One drop of this solution -93

(0.05m1.) was applied to a drop-reaction paper that had been impregnated with an alcoholic solution of rubeanic acid and then dried. In the presence of copper, a dark-green spot was obtained. By dissolving pure bismuth phosphate in the some manner and adding suitable amounts oftopper, the amount of copper present in the precipitates could be estimated. The limit of detection was found to be about Q.O.9na of copper in 9.nl. of solution. The following results were obtained.

Weight of Weight of Wt, of Cu in Bi taken, Cu taken. precipitate. 150mg. 5Crig Less than 0.05mg. 150mg. 150mg. Less than 0.05mg. 150mg. 30Cmg. Approx. 0.05mg. 150mg. 50*. Approx. 0.1mg. The above taste were repeated and the same order of results was obtained. In a further series Of determinations, the bismuth was precipitated by the bismuth phosphate mannitol method in the presence of 500 g. of copper. The precipitates were filtered and washed as usual. After ignition, they were dissolved in hydrochloric acid and tested for copper as already described. The following volumes of standard, bismuth solutionweremeasured at 16°C. 1. ,m1. 2. 10m1. 3. 25m1.. is. 50m1. These volumes corresponded to weights of bismuth between 3Ong. and 300mg. The copper in the filtrates was determined by.the iodcmetric method as described by Hillebrand of al. (loci cit.). The following results were obtained. -94-

Paloulated retermined wt. flg. of Cu in of LUPO . of .iron. precipitate. 0.0449g. 0.0450g. Less than 0.05 0.0449g. 0.0450g. Less than 0.05 0.0897g. 0.0899g. 0.05 to 0.1 0.0897g. 0.0897g. 0.05 to 0.1 0.2237g. 0.2238g. About U.1 0.2237g. 0.2239g. About 0.1 0.4469g. 0.4467g. About 0.]. 0.4469g. 0.44688. About 0.2 The quantities of nitric acid, ammonium phosphate and mannitol present in the filtrates were shown to be without effect on the volumetric determination of copper by the iodometric method. However, the determinations were not accurate enough to enable the small losses of copper to be detected. Cadmium. A standard solution of cadmium was prepared by. dissolving 8.2670g. of 'spec.-pure' cadmium in 500.11. of diluted (1+ 1) nitric acid and diluting to 100Gml. with water at. 25°C. In the following determinations the volumes of the standard cadmium solution calculated to be equivalent to the stated mighty, were measured from a burette. In all determinations 25111. of the standard bismuth solution were measured at 21°C. The weight of bismuth taken was 0.2483g. It was necessary to weigh the precipitates as no satisfactory method was found for the estimation of the coprecipitated cadmium. However, the following qualitative test was found to be useful. The precipitate was boiled far five minutes with 5m1. of 4N-annonium hydroxide solution and the liquid filtered. The filtrate was just acidified with acetic acid and the -95..

cadion 23 test applied. (See F eoigl loc. cit.). The follo.ling results were obtained. Weight of Calculated wt. Determined wt. Cd taken. of BiPO4. of 13iPO4. Nil. 0.3613g, 0.3611g.

27g• 0.3613g. 0.3612g. 50ng. 0.3613g. 0.3619g. 250mg. 0.3613g. 0.3630g. 4OCig. 0.3613g. 0.3648g. The weights of cadmium in the precipitates were 0.0mg., 0.amg. and Lang. (Calculated assuming the cadmium to be present as Cd (PO4)2). The precipitates were exanined by the qualitative tests already described; cadmium was detected in the last three precipitates. Splenium. A stock solution of selenium was prepared by dissolving 8.32g. of Na20003.51120 in 250n1., of water. The solution was filtered just before use. This solution contained approximately 10mg. of selenium per The selenium in the precipitates was estimated by dissolving then in diluted (li-2) hydrochloric acid and diluting the solution to 50m1. with acid of the same concentration. To, this solution were added 5111..of 10. per cent. hydrazine hydrochloride solution and 10m1. of saturated sulphur dioxide solution. The yellow to pink colouration that developed in the presence of small amounts of selenium was matched against etandarde. When larger amounts of selenium were present, the elementary selenium was allowed to settle, filtered on a porous-based crucible, washed with diluted (1+2) hydrochloric acid, alcohol and ether, dried in the oven at 105°C. and weighed. — 96 —

A dilute solution' o.f selenium was prepared by diluting 10711. of the stock solution to 100111. with water. In the following tests the weight of bismuth taken was 250mg. Weight of Weight of Method of Se taken. Se in ppt. estimating_., Se. lmg. MMg. • Gravimetrically. long. The second determination was abandoned because the whole solution turned milky on the addition of the ammonium phosphate solution and the precipitation of the bismuth was not quite complete (about'0.5mg. Bi in the filtrate). Y911urilrl. A stock solution of tellurium was prepared by dissolving 4.97g. of Kje06 in 25Q'nl. of water. The solution was filtered just before use. This solution contained about 10!!g. of tellurium per ml. The tellurium in the precipitates was estimated exactly ae described for selenium. The only modification being that in the gravimetric method the solution was heated to boiling to help'coagulate the precipitated tellurium. A dilute solution of tellurium was prepared by diluting 10m1. of the stock solution to 10Dml. with water, In the following tests the weight of bismuth taken was 250mg.

Weight of Weight of Method of Te taken. Te in ppt. estimating Te. 0.4mg. Colorimetrically 10m g. 2.7ings Gravimetrically. The gravimetric result for tellurium is likely to be. high awing to the coprecipitation of bismuth salts and also to the oxidation of the tellurium to the dioxide. I m. In the following tests the iron was weighed out as iron powder and dissolved in the minimum amount of diluted (14.1) nitric acid. The weight of bismuth taken was 25Ong. The following qualitative test was used to give an indication of the amount of iron present in the precipitates. The precipitates were dissolved in 10ml. of 2N-hydrochloric acid, the bismuth was precipitated by hydrogen sulphide and the solutions were filtered through 9-on. No.41 WhatMan filter papers. The filtrates were heated to boiling and boiled to expel most of the excess of hydrogen sulphide, oxidised with bromine and made alkaline with aqueous amnonia. After heating to boiling, the solutions were set aside for ten minutes. Lithe presence of 0.1mg. of iron, the precipitate was difficult to see, but 0.2mg. of iron was clearly visible. In the presence of 50Ung. of iron, no precipitate was formed even when the solution wan diluted to 40Un1. After standing on the hot-plate for one hour the solution was opalescent, but no precipitate settled out. An inberes-. ting observation was made by Keschan(339) who failed to get complete precipitation of phosphate by bismuth nitrate solution in the presence of ferric iron. He claimed that the phosphate was completely precipitated when the iron was reduced to the ferrous state. In the presence of 10mg. of iron, the bismuth phosphate MS slaw' in forming. The bulk of the precipitate did not separate until the solution was diluted with water; this precipitate was very finely divided. The precipitation of the bismuth was incomplete and the precipitate contained -98- about 0.15me. of iron. Aluminium. In the following tests the aluminium was weighed out as aluminium foil and dissolved in the minimum amount of 2N-sodium hydroxide solution. The solution was then acidified with diluted (1+ 1) nitric acid. Aluminium was sought in the precipitates by the method already described for iron except that one drop of methyl red solution was added before the aqueous ammonia. This served two purposee, one to adjust the pH to the correct, value for the precipitation of aluminium hydroxide and the other to colour the precipitate, thus rendering it easier to see. As this test is at the best only a semi-quantitative one, the bismuth phosphate was filtered and weighed before the test was applied. The weight of bismuth taken was 0.1838g., which is equivalent to 0.2673g. of bismuth phosphate. The two weights of biseuth phosphate found with 500mg. of aluminium present were 0.2703g. and 0.2704g. Therefore, the bismuth phosphate contained about 3mg. of aluminium phosphate or about 0.6mg* of aluninium. The qualitative test described above indicated the presence of about 0.51g. of aluminium when compared with standards of 0.2mg., 0.5mg. and 1.0mg. Indium. In the following tests the indium was weighed as metal and dissolved in the minimum amount of nitric acid. The weight of bismuth taken was 2501eg. The following method was used to estimate the indium in the precipitates. The precipitate and paper were dried in the oven at 105°C. The precipitate eras detached from the paper into a dry 35-ml. glasa-otoppered weighing bottle and dissolved in 5m1. of diluted (1d-1) hydrobrcmic acid. To this solution were added lOnl. of diethyl ether; the bottle was stoppered and shaken. -99-

The ether layer was allaweA to separate and transferred with a transfer pipette into a 400-ml. Phillips beaker. The ether was evaporated on the water-bath and to the residue were added 2m1. of diluted (14-1) nitric acid and 0.5ml. of perchioric acid. The solution was evaporated until fumes of perchloric acid were evolved and the condensed nitric acid was evaporated by blowing a stream of hot air fran a Bylock industrial air-blower across the mouth of the beaker. The solationvmm diluted to 200m1. with water, heated to 60QC. and the indium titrated with.0.025M-E.P.T.A. solution. The indicator used was xylenol orange. With 100mg. of indium taken hmg. were found in ,the precipitate. With 500mg. taken indium phosphate precipitated on diluting the solution. Chromium. In the following tests, the chromium was, weighed out as chromium pal er and dissolved in the minimum amount of diluted (14-1).nitrie acid. The following method was used to estimate the amount of chromium coprecipitated with the bieluth phosphate. The precipitates were fused with a mixture of sodium carbonate and sodium. peroxide in nickel crucibles and the cold melts'uere extracted with water. The solutions were filtered and the filtrates were collected in 100-ml. Nessler cylinders. The colours were compared with a set of standards prepared from potassium chromate. With 250mg. of bismuth and 50Ong. of chromium, the mount of chromium found in the precipitate was O.3ng. . With,25Cmg. of bismuth and 5Ong. of chromium, the mount was less than 0.05mg. Beryllium. In the following tents, the beryllium was weighed out as hydrated beryllium carbonate and dissolved in the minimum amount of diluted (1+1) nitric acid. Beryllium was sought in the precipitates by the method already described for aluminium. The limit of detection was about 0.2mg. With 250/T. of bismuth and 50mg. of beryllium taken, the amount of coprecipitated beryllium was less than 0.2mg. Ceriut. In the following tests the cerium was weighed out as hydrated eerie ammonium nitrate and dissolved in a few ml. of diluted (1+1) nitric acid and the resulting solution was diluted with water. Cerium was sought in the precipitates by the method described for iron except that hydrogen peroxide was used in place of bromine water. However, the precipitate was too large for comparison with standards and, therefore, the cerium hydroxide was filtered, washed and ignited to eerie oxide in a platinum crucible. The precipitate will contain phosphorus. With 25Chg. of bismuth and 50mg. of cerium, the amount of coprecipitated cerium was 2.5mgo It was noticed that when the solution was heated to boil— ing prior to the precipitation of the bismuth phosphate the cerium was reduced to the to rvalent state with the evolution of formaldehyde. Thorium. Titanium and Zirconium. Mixtures of the above elements with bismuth mere.not investigated as it was shown that these elements were quantitatively precipitated by the phosphate mannitol method. Zink. A stock solution of zinc was prepared bit dissolving 5.00g. of AnalaR 101 zinc in 25m1. of diluted (1+1) nitric acid and diluting the solution to

500ml. with water. The zinc in the precipitates was estimated by dissolving then in Mile of diluted (1+ 1) hydrochloric acid, diluting the solution to 501t1. with water in a Nessler cylinder and adding 2en1. of saturated potassitrn terra- cyanide solution in diluted (1+9) hydrochloric acid. After ten minutes, the opalescence was compared with standards prepared from pure bismuth photo- phate ani a diluted standard zinc solution. The limit of detection was about 0.02mg. of zinc in 50n1. of diluted (1+9) hydrochloric acid. When the potassium ferrocyanide solution was made up in water, an opalescence was produced with bismuth even when zinc was absent. The following results were obtained. Weight of Weight of Weight of 13i taken. Zn taken. Zn in ppt. 25Ong. 250ng. 0.09ng.

250ntg. 50Oug. 0.2ttg. ?iicitel. A stock solution of nickel was prepared by' dissolving 5.00g. of AnalaR nickel foil in a mixture of 20n1. of diluted (1+ 2) nitric acid and 20n1 of 20-vol. hydrogen peroxide. The solution was boiled for ten minutes to destroy most of the excess of hydrogen peroxide and then the solution was diluted to 500m1. with water. The nickel in the precipitates was estimated by dissolving then in 2an1. of 2N-hydrochloric acid, adding 2g. of tartaric acid, 20n1. of 104. arnicalium hydroxide solution and 9n1. of a 5 per cent alcoholic volution of dimethylgl,yoxirne. After keeping for ten minutes, the pink colour was -102- compared with standards prepared from pure bismuth phosphate and a diluted standard nickel solution. The limit of detection wan about 0.05ng. of nickel in 50m1. of solution. The following results were obtained. Weight of Weight of Weight of Si taken. Bi taken. Ni in ppt. 250mg, 250mg. Less than 0.05mg. 250mg. 500mg. Less than 0.05mg. Cobalt. A stock solution of cobalt was prepared by dissolving 5.00g. of pure cobalt metal in a mixture of 20m1. of diluted (1+2) nitric acid and 20m1. of 20-vol. hydrogen peroxide. The solution was boiled to destroy most of the excess of hydrogen peroxide and the solution was then diluted to 500m1. with water. The cobalt in the precipitates was estimated by dissolving then in 50m1. of 2N-hydrochloric acid, saturating .the solution with hydrogen sulphide and filtering off the precipitated bismuth sulphide. The solution was boiled to expel hydrogen sulphide, cooled and transferred to a Hessler cylinder. To this solution was added an excess of solid ammonium thiocyanate.. The blue- green colour due to the complex cobalt thiocyanate was developed by addillg an equal volume of acetone. When 30C) g. of pure biemuth phosphate were dissolved in 5001. of 2NAlydrodhloric acid and 1ml. of a solution containing 0.05mg. of cobalt, was added and the above procedure followed, a blue-green colour developed on adding the acetone. The following results were obtained. Weight of Weight of Weight of Bi taken. Co taken. Co in ppt. 250mg. 250mg. Less than 0.05mg. 250mg. 500mg. Less than 0.05mg. -103-

diarranesp.

The weight of manganese taken, was obtained by weighing pure manganese oxide (MA). This was dissolved in 15n1. of Mienitrie acid with theaddi.. tion of a crystal of sodium nitrite. If the sodium nitrite was not added a brown opalescence remained after the bulk of the oxide had dissolved. As no satisfactory material was available for preparation of the standard manganese solution, the manganese oxide was prepared Iran pure manganese chloride by the following method. The manganese chloride was dissolved in water and manganese carbonate was precipitated by the addition of ammonium carbonate solution, the precipitate was filtered and washed with hot water until it was free Fran chloride. The preCipitatewas removed /ran the paper and dried in a current of nitrogen. The oxide was then ignited at a temperature of 800°C. in an atmosphere of nitrogen. The oxide was bright green in colour and an X-ray powder photograph failed to show the presence of any oxide other than !W. The manganese in the precipitates was estimated by washing then into a

150 -ml. beaker with the minimum quantity of hot water, evaporating off the water on a steam-bath and diesolving the bismuth phosphate in 7.51. of concentrated nitric acid. The solution wan then diluted to 75n1. with water, 0.2g. of potassium periodate was added and the solution was boiled for about ten minutes to develop the permanganate colour. The bismuth phosphate was reprecipitated when the solution was diluted with water. A standard was prepared by dissolving 380mg. of pure bismuth phosphate in 7.5m1. of concentrated nitric acid, adding 1ml. of a solution containing 0.0571g. of manganese per ml. and then treating as above. The colour developed in. the 104.. standard was compared in the beakers with the colours obtained from the precipitates. The following results were obtained. Weight of Weight of Weight of Bi taken. Mn taken. Mn in ppt. 250mg. 250mg. Less than 0.05mg 250mg. 500v. Less than 0.05mg. Tlagnes um. The magnesium in the precipitates was detected by the following method. The bismuth phosphate was dissolved in lOml. of 2N-hydrochloric acid and the bismuth was precipitated by hydrogen sulphide (it was found to be desirable to wash the hydrogen sulphide gas by bubbling it through two test tubes full of water to remove all traces of iron; iron was found to interfere in the next stage), the bismuth sulphide was filtered and weshedwith water saturated with hydrogen sulphide. The combined filtrate and washings were boiled. oxidised with a small excess of bromine water and again boiled to expel the excess of bromine. The solution was cooled, two drops of methyl orange indicator solution were added and the solution was neutral seed with 4N- ammonium hydroxide solution. To the solution were added a minute crystal of sodium hydrosulphite to decolourise the solution and then 2m1. of 4N- &Timonium hydroxide solution. To this solution was added sufficient Brio Chrome Black T indicator mixture (1g. of Erlo Chrome Blank T and 200g. of sodium chloride ground to an intimate mixture) to give a suitable colour intensity. In the presence of magnesimns the solution was purple in colour; on adding 0.01N E.D.T.A. solution the colour changed to pure blue when all the magnesium was ccmplexed. The solution of E.D.T.A. was added 0.1m1. at a time from a micro-pipette until the colour of the solution was pure blue. 105

Each addition of E. ?.f.A. was eeuivalent to 0.024mg. of magnesium) this amount was about the minimum quantity of magnesium that could be detected. In the following test the magnesium was weighed out as magnesium turn— ings and dissolved in the minimum amount of diluted (1+1) nitric acid. `4ith 5O0mg. of magnesium and 25U mg. of bismuth the amount of coprecipitated magnesium was about 0.05Ins.

Calcium. The calcium in the precipitates was detected by a method similar to that described for magnesium. However, it was found that a better colour was obtained for the calcium if a small amount of magnesium and its equiva— lent of E.D.T.A. were added. In the following tests the calcium was weighed out as Anala calcium carbonate and dissolved in the minimum amount of diluted (1+1) nitric acid. With 5Dr3mg. of calcium and 250mg. of bismuth, the amount of coprecipitated calcium was 1.CMg. With 50mg. of calcium and 250mg. of bismuth, the amount was 0.08mg. Strontium and Barium* The strontium and bariuM in the precipitates were determined by exactlY the same method as described for calcium. In the following tests the strontium and barium were weighed out as carbonates and dissolved in the minimum amount of diluted (1+1) nitric acid. The weight of bismuth taken was 250 g. Element Wt. of element Wt. of element taken. taken. in the ppt. Sr 500mg* ©.fang. Sr 100mg. 0,15mg.

Ba 500mg, 0.3mg.

Ba 2001g. Less than 0.3mg. Pummarx of Og Separations thatffire posql.W.a Diemuth4liospbapv MethoA.

The following elements were shown to interfere with the method and must be separated before precipitation of bismuth as the phosphate:- indium, lead, arsenic, antimony, tin, selenium, tellurium, molybdenum, titanium, thokum, eirefimium and cerium. The following elements were shown not to interfere with the mannitol method when present in the amounts shown after each element. The element was considered to be non-interfering if less than tang. was coprecipitated with the bismuth phosphate. Separations were obtained with the following elements:- copper(500mg. maximum amount tested), cachium(56mg.), mercury silver(54mg.), iron(1Qmg.), aluminium(200mg.), chromium(1460mg.), berylliUm(50mg. maximum amount tested), zinC(500mg. maximum amount tested), cobcdt(500ng. maximum amount tested), nickel(500mg. maximum amount tested), mangarteee(500mg. maximum anount tested), thai ipm(150ng. )p Calcium W(kng. )0 strontium(2oomg.), barium(350mg.) and magnesium(500mg. maximum amount tested). gonfirmation of Results in 1 heLBism411-41losphate Mannitol Method. The following results were obtained by 1.14 Fowler, B.Sc., -A.R.C.S. For details of the methods of analysis used see pages 59, 66-67 and 85-86. The weight of bismuth taken was equivalent to 0.3389g. of bismuth phosphate. Method Wt. of BiPO4 obtained.

Schoeller & Lanbie 0.3378g., (43377g+

Hillebrand & Lundell 0.33e0g., 0.3381g•

Mannitol 0.3386g., 0.33e7g. 10'7 —

The following resultn were obtained by A.E. Purkisp Grad.R.I.C.

?lethod Calculated 1%. Wt. of BiSD14 of 3iPO4. obtained. Schoeller& Lambie 0.2839g. 0.2818g., 0.2819g., 0.2821g. Mannitol 0.2838g. 0.2840g., 0.2839g. Viannitol 0,2279g. 0.2279g., 0.2277g. -108-

LXamination of the E.p.T.A. Titration.

Free Acid Concentration.

One of the difficulties in applying the E.D.T.A. method in practical

analysis is to obtain a nitrate solution with the correct amount of free

acid present. If the neutralisation of any excess of acid is attempted by means of aqueous ammonia (the method recommended in the published methods)

and a slight excess of alkali is &Med, a precipitate is formed and this requires an excess of acid for dissolution. The solution is then too acid for the titration arri must again be neutralised with aqueous ammonia.

This type of neutralisation does not lead to a constant concentration

of acid, as the free acid required to keep the bismuth in solution will be dependent on many factors such as the total salt concentration (and therefore the amount of excess acid originally present), the temperature, the

amount of bismuth present and the method of adding the aqueous ammonia.

One way of overcoming this difficulty is to evaporate the solution to

a constant volume with a non-volatile acid and thus to expel the volatile

acids present. The obvious choice when working with bismuth is perchloric

acid.

Bismuth Solution. Bismuth metal (1.0537g.) was dissolved in 5m1. of diluted (1+1) nitric

acid in a 650-ml. Phillips beaker, 5m1. of 60 per cent. perchioric acid were added and the solution was evaporated until fumes of perchioric acid were evolved. The nitric acid condensed on the sides of the beaker was removed by blowing a stream of hot air from a Bdock industrial air blower across th© mouth of the beaker. The solution was cooled, transferred to a 250-ml. - 109 - volumetric flask and diluted to volume with water. Diluted Bismuth Solution. Bismuth solution (12.11.) and 1ml. of perchloric acid diluted to 100m1. with water. Each millilitre is equivalent to 0.1m1. of E.P.T.A. AP.T.A. Solution. Prepared as is described on page 61. Pvroeateehol Violet Indicator Solution. Catechol violet (0.1g.) dissolved in 100m1. of cold water. Perchloric Acid. 60 per cent. w/W.HC10 Method of Titration. Into a 650em1. Phillips beaker were pipetted 5111. of the bismuth solution. To this solution were added the volume of perchloric acid shown in the table below, 249ml. of water and 0.2m1. of the indicator solution. The solutions were titrated with the E.D.T.A. solution fro a 5.1m1. micro-burette

• sub-divided in 0.02m1. During the titration the beaker was placed on a sheet of frosted glass that was illuminated from beneath by a fluorescent lamp. (The titration until was manufactured by Griffin t George Ltd.). The colour of the solution being titrated was. always compared with the colour of a solution that contained the same amount of reagents and had been over-titrated. The titration was continued until the colours matched. To the titrated solution wan added, from a micro-pipette, 0.1m1. of the diluted bismuth solution. If a difference in colour was now observed between the two solutions, the first reading of the burette was taken as the titre. If — 110 —

no change in colour was observed, a further 0.1m1. of the diluted bismuth solution wan added. If a change in colour Was now observed 0.01m1. was deducted frcm the reading of the burette to give the titre. The process was repeated once more if necessary. If the solution was over-titrated by more than 0.02m1., the titration was repeated. During the titration the colour of the indicator changes from pure blue to magenta and from magenta to pure yellow. An intermediate colour, described as full magenta, was chosen and was kept as a reference for all the following titration. This colour wan produced by adding to 2.50m14, of water 0.2m1. of the diluted bismuth solution, 0.1n1. of perchloric acid and

0.2111. of the indicator solution. T41. of Perchloric acid 0 1 2 3 Full magenta 3.9 3.7 3.2 2.5 End-point 3.92 -342 3.93 3.92 Notes (1) (2) (3) (4)

(1) The total acid concentration was about 0.1m1. of perchloric acid in

250m1. The end-point colour was pure yellow.

(2) The end-point colour appeared pure yellow but, on ccmparison with the first solution, a very slight red tint was detectable.

(3) The end-point colour appeared/reddish yellow but, when compared as' described with an over-titrated solution, the end-point was very sharp. (4)The end-point colour was reddish yellow but, when compared as described with an over-titrated solution, the end-point was sharp.

Cpnclusions.

A concentration of imi. of free perchloric acid per 250m1. of solution gives eel end -point. This concentration of acid is preferable to the 002ml. per 250m1., firstly, because it is easier to realise in practical analysis, secondly, because a warning of the end-point is obtained in plenty of time to avoid overshooting the end-point and thirdly, because it should make the titration more selective. Satisfactory results can be obtained with acid concentrations up to 2m1. of perchloric acid per 250m1. A concentration of 1ml. of perchloric acid per 250nl. has bemused in all subsequent work on the sovr.A. method. Chas, of Indicat9r. Into a 650.1611. Phillips beaker were pipetted 5m1. of the standard bismuth solution. To this solution were added ]ml. of perchloric acid, 24551. of water and sufficient quantity of the indicators to colour the solutions. The following titres were obtained. Indicator Titration Olean of 3) Catechol Violet 3.92m1. Xylenol Orange 3.94m1. Methyl Thrnol Blue 3.95m1. Potassium Iodide (250eg.) 3.92m1. Pyridyl-aso-naphthol Solution too acid to titrate with this indicator. Conclusions. The use of catechol violet is preferred, firstly, because the indicator is readily soluble in water and the solution is stable, secondly, because of the intermediate colour change that gives warning of the end-point and thirdly, because of the instantaneous reaction of the coloured metal-indicator conplex with the .D.TiA. Determine ion of isrttuth in the Presence of some Other Ions. The first type of interference to be examined was the effect of small amounts of foreign anions such as might be introduced during the separations necessary in the analysis of complex materials. Bismuth solution.- BisMuth metal (4.0g.) was weighed into a 650oml. Phillips beaker and dissolved in 20ml. of concentrated nitric acid. Thin solution was cooled, transferred to a 1-litre volumetric flask and diluted to 1 litre with water. Dklutpo Bismuth Solution, The solution described on page 109 WAS used. TIOhod of Titratior%. To a 650 1. Phillips beaker were added 5m1. Of the bismuth solution, 1ml. of perthloric acid and the anion being. tested. The solution was eve- porated to fumes of perchloric acid and the acid condensed on the sides of the beaker was evaporated by blowing a stream of hot air from a Bylock industrial air blower across the mouth of the beaker. The solution was diluted with 250m1. of water and titrated with B.D.T.A. solution as is described on pages 109-110. Chloride. A standard solution of chloride was prepared by dissolving 1.65g. of sodium chloride in 100711. of water. Each millilitre of this solution is equivalent to 1.0Mg. of chloride. Three solutions were prepared in duplicate containing (1) No chloride, (2) lmg. of chloride and (3) 10mg. of chloride. (1) The end-points were normal and the titres were 3.86m1. and 3.86m1. -113 ..

(2)A small amount of white precipitate separated just before the perchloric acid fumed. This dissolved during the fuming. On dilution with water, the solutions were just opalescent. The end-points were normal and the titres were 3.66n1. and Mad.. (3)A white precipitate separated from the nitric acid solution but dissolved when the perchioric acid was fumed* On dilution with water. the Solutions were cloudy.. The end-points appeared after about 1.5ml. of B.P.T.A. solution had been added, but the red colour soon, drifted back and no satisfactory end- points could be reached. The addition of a total of hml. of E.D.T.A. solution failed to clear the solution. The interference of chloride could possibly, be removed by precipitating the chloride byr silver nitrate solution. Theoretically 1ml. of 5 per cent. silver nitrate solution should precipitate 10g., of chloride. Therefore, the above three tests were repeated, but to each solution was added 1ml. of silver nitrate solution (0.5g. of silver nitrate in 10m1. of water) prior to evaporation with parchioric acid. (1), The end-points were normal and the titres were 3.86m1. and 3.86m1. (2)A white precipitate fanned on adding the .silver nitrate solution. Dur- ing the evaporation, the precipitate coagulated and when the solutions were diluted .with. water the resultant solutions'uere bright, but a small amount of precipitate lay on the botton of the beakers. The end-points were normal and the titres 3.86m1. and 3.86m1. (3)A white precipitate formed on adding the silver nitrate solution. During the evaporation the precipitate coagulated and when the solutions were diluted with water the resultant solutions were cloudy. The end-points were normal and the titres 3.52m1. and 3.5&1. Test. (3) was repeated but this time 2ml. of silVer nitrate solntion mere added. The tests behaved as is described under (2) on the'previCes page. The end-points were normal and the titres 3.8&1. and 3.86m1. arcmide. A standard .solution of bromide was prepared by dissolving 1.49g. of potassium bromide in 100n1. of water. Each millilitre is equivalent to 10mg. of bromide. Three solutions were prepared in duplicate containing (1) no bromide, (2) lmg. of bromide and 10mg. of bromide. (1)The end-points were normal and the titres were 3.86m1. and 3.8(1. (2)During the evaporation free bromine was evolved. The end-points were normal and the titres 3.86m1. and 3.85m1. (3)During the evaporation free bromine was evolved. The end-points were normal and the titres 3.86m1. and 3.86m1 Sulphate. A standard solution of sulphate was prepared by dissolving 1.82g. of potassium sulphate in 100m1. of water. 'Each millilitre is equivalent to lOng. of sulphate. Three solutions were prepared in duplicate containing (1) no sulphate, (2) Ing. of sulphate and (3) 10mg. of sulphate. (1)The end-points were normal and the titres were 3.86m1. and 3.8(1.

(2) No precipitate was formed either during the evaporations or on dilution of the 'Solutions before titrations. The end-points were normal and the Utica 3.86m1. and 3.86m1S (3) NO pr pitaste formed during the evaporations but small precipitates were preeent during the titration. The end-pante appeared after about 1.911. of W..A. solution had been added, but the red colour coon drifted back and no satisfactory end-points Could be reached. The aMition of a total of 4m1 of EIM.T.A. solution failed to clear the solutions. The interference of eulphato could possibly- be removed by precipitating the sulphates by nitrate solution. Theoretically 1ml. of 3 per cent. barium nitrate solution should precipitate lOng* of sulphate. Therefore the above three tests were repeated, butte, each solution was adeed let. of barium nitrate solution (0.3(. of barium nitrate in 10m1. of water) prior to evaporation with perchioria acid . (1) The end-points were normal and the titres w and 3.86m1. (z) A email amount of precipitate separated during the evaporation. The endepointe were normal ane the titres were 3.Sbml. and 3.86m1. (3) A precipitate formed on adding the barium nitrate volution. When the soluticcae were diluted for titration the resultant eolutions were bright. The endepoirste were normal and the titres were 3.'7& 1. and 3.e0n1. Test (3) won repeated but this time 2t1. of the bariun nitrate solution were added. The tests behaved as dencribed under (3) on this page. The endepoints e normal and the titren were 3.80M10. and 3.B l.. If soluble sulphate wan the cause of the law resulte obtained in test (3) then increasing the barium ion concentration would be expected to reduce the interference. Although the results are .lightly nearer the theoretical, the titration in et ill too small. The reason for this in probably coproci- pitation of bismuth with the barium eulphate. Fluoride. Because of the difficulty of storing and measuring fluoride solutions with glass apparatus„weights of solid potassium fluoride were weighed out for each determination. To obtain lmg. of fluoride, 3.O5ng. of potassium fluoride are required. Three solutions were prepared in duplicate containing (1) no fluoride, (2) 3mg. of fluoride and (3) lam. of fluoride. (1)The end-points were normal and the titres were 3.86m1. and 3.85m1. (2)The solutions were clear at all stages of the process. The end-points were normal and the titres were 5se6ml. and 3.86111. (3)The solutions were clear at all stages of the process. The in s were normal and the titres were 3.e&nl. and 3.86m1

A standard solution of borate was prepared by dissolving 5.7l. of boric acid in 100m1. of water. Each millilitre is equivalent to 10mg. of boron. Three solutions were prepared in duplicate containing (1) no boron, (2) Ism. of boron and (3) 10mge of boron. (I) The end-points were normal and the titres were 3.85m1, and 3.851. (2)No precipitate was fanned either during the evaporations or on dilution of the solutions before titration. The end-points were normal and the titres were 3.89ml. and 3,85,14 (3)No precipitate was formed either during the evaporations or on dilution of the solutions before titration. The end-points were normal and the titres were 3.85m1. and 3.85r111. - 331 -

Phosphate. A standard solution of phosphate was prepared by dissolving 4.26g. of diammenium hydrogen phosphate in 100m1. of water. Each millilitre is equivalent to lOng. of phosphorus, Two solutions were prepared in duplicate containing (1) no phosphorus, and (2) lmg. of phosphorue. (1)The end-points were normal and the titres were 3.85n1. and 3.85m1. (2)Precipitates were fanned on the addition of the enmonium phosphate solu. tion but dissolved when the perchloric acid fumed. When the solutions were diluted with water the precipitates were re-formed. The first end-points appeared after about 2.6ml. of E.P.T.A. solution had been added but the red colour returned rapidly and no satisfactory end-points could be reached. After adding 4.00n1. of E.P.T.A. solution the precipitates dissolved and the excess of the E.D.T.A. solution was back-titrated with the diluted bismuth solution. The final volume of E.P.T.A. solution used in the titrations were 3.83m1. and 3.81n3.. Conclusions. The E.P.T.A. titration of bismuth follcwing evaporation to fumes with a mixture of nitric and perchloric acids is unaffected by the presence of lOng. of bromide, fluoride or boron (present as borate). The titration fails in the presence of lmg. of chloride or phosphorus (present as phosphate) and in the presence of more than lmg. of sulphate ion. The interference of chloride can be completely eliminated by the addi Lion of silver nitrate. The interference of moderate amounts of sulphate can be reduced to a lad level by the addition of barium nitrate. Correct results can be obtained in the presence of small amounts of phosphate by adding an excess of EX.T.A. solution and back-titrating the excess of E.P.T.A. with a standard bismuth solution. This method does not work for chloride or sulphate., The second type of interference to be examined was the effect of other metal ions. The general method used was to weigh the weight of interfering metal required into a 650-m1. Phillips beaker and to add sufficient diluted (14- 1) nitric acid to dissolve it. To this solution were added 5111. of the sten. dard bismuth solution and sufficient perchioric acid to convert the other metal to the perchlorate and to leave an excess of lml. of free perchloric acid. The solution was evaporated to fumes of perebloric acid and treated as described on page 112 for the titration of the bismuth. When aluminium was tested the metal was dissolved in 5N-sodium hydroxid ablution, the resulting solution was acidified with diluted (1+1) nitric acid and treated as described above. The solutions for the alkali and alkaline-earth metals were prepared from the carbonates and not the metals. As the addition of ascorbic acid is claimed to prevent the interference of mercury and iron, the effect of the presence of this acid was =mined. Ancor* Acid. Four solutions were prepared containing (1) no ascorbic acid, (2) 1g of ascorbic acid, (3) 2g. of ascorbic acid and (4) 5g. of ascorbic acid. (1)The end-point was normal and the titre was 3.85m1. (2)The initial colour of the solution had a definite green tint and the full magenta colour of the indicator was developed earlier than usual. The - 119

colour change at the end-point was normal and the titre was 3.85m1. (3)The solution titrated as described above for (2). The titre was 3.89n1. (4)The initial colour of the solution had a definite green tint and the full magenta colour of the indicator was developed much earlier than usual. The end-point was very sharp but t1:0 colour of the indicator had a red tint When compared with solution (1). The titre was 3.85n1. karl. Four solutions were prepared containing (1) no lead, (2) 100mg. of lead, (3)250ngs of lead and (4) 50ang. of lead. All four solutions had identical end-points and titres of 3.89m1. Copper. Five solutions were prepared containing (1) no copper, (2) 9ftg, of copper, (3) 10mg. of topper, (4) 501g. of copper and (5) 100mg. of copper. When titrating bismuth in the presence of copper it was impossible, when much copper was present, to obtain an end-point before an excess of E.D.T.A. solution had been added. This excess of E.P.T.A. solution was back- titrated with the diluted bismuth solution from a 5-ml. micro-burette. In the following results therefore, the titre is given and after the titre in brackets is given the volume that was deducted from the initial titre. In the direct titration of bismuth in the presence of copper the titre recorded would be the sum of these two figures. (1)The end-point was normal. and the titre was 3.85n1. (2)The colour change at the end-point was a little slower than usual but the colour changes were normal and the titre was 3.85n1. (0.02m1.). (3)After the pure blue colour of the indicator had been discharged the colour changed through a red to a neutral grey that eventual:ly turned yellow at the end-point. The colour change at the end int was very slow. The titre was 3.85e. (0.0bml.). (4)The solution titrated as described above for solution (3). The titre was 3.81n1. 09.24m1.). (5)The solution titrated as described above for solution (3). The titre was 3.8811. (0.25711.). When an unknown solution is being titrated for bismuth, the presence of copper in interfering amounts is readily shown by the blue colour of the perchloric acid after the evaporation. The 5mg. of copper was readily vie- ible. The 5mg. and Wig. of copper were not visible after dilution with water but the 50mg. and la b& were. Morrow. In order to investigate the effect of the presence of mercury in either valency state, the mercury was added in the form of mercurous nitrate or mercuric oxide and not se the metal. The mercurous nitrate was added after the evaporation with perchloric acid to prevent oxidation during the fuming of the perchloric acid. (a) Mercury I. The weight of mercurous nitrate mono-hydrate required to give Img. of mercury is 1.40mg. The mercurous nitrate was weighed out and dissolved in 250m1. of water containing ©.]ml. of perchloric acid. This solution was used for the dilution after the bismuth solution had been evaporated to fumes with perchloric acid. Three solutions were prepared containing (1) no mercury, (2) 50mg. of mercury I and (3) 5001g. of mercury I. (1)The end-point was norylal and the titre 3.25m1. (2)The end-point was normal and the titre was 3.89n1. (3)The e'nd•point was more drawn out than usual and the solution became turbid during the titration. The titre was 5,0mls (b) ►'tercury II. The weight of mercuric oxide required to give lmg. of mercury is 1.081g. The mercuric oxide was weighed into a 650-ell. Phillips beaker and the bismuth solution was added. The solution was then prepared for titration as isdes- cribed on page 112. Three solutions were prepared containing(1) no mercury, (2) 50mg. of mercury II and (3) 50CMg. of mercury II. (1)The end-point was normal and the titre was 3.85m1. (2)On adding the E.fl.T.A. solution, a precipitate was formed and no end» point could be detected. (3)The solution titrated as is described above for solution (2). The, use of ascorbic acid has been► recommended to prevent the interference of mercury with the titration (Cifka et al. Ref. 307). The use of ascorbic acid, when titrating under the conditions described on page 112, was not satisfactory. The mercury was reduced to the element very sloWly and it was impossible to coagulate the mercury so that the colour change of the indicator could be seen clearly. palm. As thallic salts are much more likely to interfere with the titration of bismuth than are thallous salts, a small amount of ascorbic acid was added to the solutions after dilution with water to ensure that all the thallium was present in the thallous state. Because of the difficulty of ensuring the oxidation of thallium in a medium that is free fran halogens, no tests were attempted with thallic salts. Three solutions were prepared containing (1) no thAllium and 100m6. of ascorbic acid, (2) 50ng. of thallium and 100 mg. of ascorbic acid and (3)

54t g. of thallium and 100mg. of ascorbic acid. All three solutions had identical end-points and titres of 3.85m1.

The use of ascorbic acid in the presence of silver is nob possible, because silver is reduced to the element, the solution darkens in colour and the end -point is difficult to see. When it was necessary to use ascorbic acid in the presence of silver, satisfactory results were obtained by the follow'.ng method. The solution was titrated to the full magenta colour of the indicator, the ascorbic acid was added and the titration was corpleted in the normal way. The reduction of silver by ascorbic acid is a slow process and therefore no darkening of the solution took place before the end-point was reached. Three solutions were prepared containing (1) no silver, (2) 50mg. of silver and (3) 500mg. of silver. All three solutions had identical end.* points and titres of 3.85m1.

Cadmium. Three solutions were prepared containing (1) no cadmium, (2) 5Ong. of cadmium and (3) 500mg. of cadmium. Al]. three solutions had identical end- points and titres of 3.85m1. - 123

Tellurium. Three solutions were prepared containing (1) no tellurium, (2) lmg. of tellurium and (3) 1Chtg. of telluriuM. (1)The end-point was normal and the titre was 3.85m1. (2)The solution was always clear, the end-point was normal and the titre was 3.85m1, (3)The solution was cloudy and the first end-point was reached after about 3.5m1. of E.D.T.A. solution had been added. The red colour soon drifted back and on adding more n.m.A. solution the process was repeated. A permanent end-point was obtained after the addition of 3.77m1. of E,T.T.A. solution. When a total of 4.00m1. of E.D.T.A. solution was added, the solution allowed to stand for five minutes, and the excess of E.D.T.A. back- titrated with the diluted bismuth solution, a titre of 3.85m1. was obtained. Lao Three solutions were prepared ning (1) no tin, (2) ling. of tin and (3) 1Dmg. of tin. (1)The end-point was normal and the titre was 3.85m1. (2)The solution was cloudy and the end-point colour had a green tint. The titre was 3.75m1. (3)The solution was cloudy and the end-point colour was green. The titre was 3.55m1+ Antim9ny. Three solutions were prepared containing (1) no antimony, (2) lmg. of antimony and (3) Ube. of antimony. (1) The end-point was normal and the titre was 3.85m1. (2)The titration was normal but the end-point colour had a slight red tint when compared with solution (1). The titre was 3.83m1. (3)The solution was cloudy and the end-point colour had a red tint. The titre was 3.65ml.

TWo solutions were prepared containing (1) no indium and (2) 10ag. of indium. (1)The end-point was normal and the titre was 3.851. (2)The end-point was normal, but the titre was 6.351. On keeping, the red colour of the indicator returned.

Two solutions were prepared containing (L) no gallium and (2) 10mg. of gallium. (1)The end-point was normal and the titre was 3.85m1. (2)No end-point was Observed in the direct titration, but after an excess of E4D.T.A. over that required to complex both the gallium and the bianuth had been added the normal end-point colour was observed. Back-titration of the excess of E.D.T.A. gave a titre that corresponded to the sum of bie r moth and gallium. 11231., The method of solution preparation used (page 112) will mean that the iron is present in the ferric state. Two solutions were prepared containing (1) no iron and (2) log. of iron. (1)The end-point was normal and the titre was 3.66m1. (2)The solution titrated normally during the first part of the titration 325 -

but the colour change near the end-point was more gradual than is usual, and the final end-point colour had a distinct red tint. The titre was 4.0m1. According to Cifka et 61.(307) the interference of iron can be prevented by reducing and complexing it by means of ascorbic acid. Therefore, the following three solutions were prepared containing CO no iron and 1g. of ascorbic acid, (2) 10mg. of iron and 1g. of ascorbic acid and (3) 100mg. of iron and 1g. of ascorbic acid. The ascorbic acid was added after the solutions had been diluted with water. All three solutions had identical end- pointe 'and titres of 3.86m1.

JibmtirniuR Three solutions were prepared containing (1) no aluminium, (2) 50mg., of aluminium and (3) 500mg. of aluminium. All three solutions had identical end-points and titres. of 3.85m1. Cerium. Thor ,um. TitaniumLand ;irconiurt. In the presence of these four elements it is difficult to obtain a clear solution, and all these elements will consume E.P.T.A. at the acidity used for the titration of bismuth. No titrations were performed in the presence of these elements, but it was assumed that they would interfere even if a clear solution could be obtained. Was l Five solutions were prepared containing (1) no nickel, (2) Img. of nickel, (3) 9mg. of nickel, (4) lOng. of nickel and (5) 100mg. of nickel. (1)The endpoint was normal and the titre was 3,85m1. (2)The end-point was normal and the titre was 3.65m1. (3)The endpoint was normal and the titre was 3.88m1. (4)The endpoint was very sharp, but the end-point colour had a slight green tint when compared with solution (1). The titre was 3,51m1. (5)The end-point was very sharp but the end-point colour was green instead of yellow. The titre was 4,45m1. Cobalt. Three solutions were prepared containing CO no cobalt, (2) 10mg. of cobalt and (3) lO)ng. of cobalt. (1)The end-point was normal and the titre was 3.86ml, (2)The end.,point was normal and the' titre was 3.86m1. (3)The end,point was very sharp but the end-point colour was modified by the pink colour of the cobalt ion. The titre was 3.86m1. Um" Three solutions uare prepared containing (1) no zinc, (2) 50mg. of rainy and (3) 5. of zinc. (1)The end-point was normal and the titre was 3.05mli (2)The end-point was normal and the titre was 3.85m1. (3)The titration was ncrmal except that the end-point colour had a slight red tint. The titre was 3.8' 1. The modified end-point colour was reminiscent of the end-point colour observed in the presence of iron. On adding a few crystals of ascorbic acid to the solution the colour changed to pure yellcw, and back-titration of the solution with the diluted bismuth solution gave a titre of 3.85n1. In a repeat of this titration, the ascorbic acid was added after dilution of the solution withwater. The end-point ues normal and the titre was 3.89a1. Maneahese. Three solutions were prepared containing (1) no manganese, (2) lane. of manganese and (3) 100mg. of manganese. (1)The end-point was normal and the titre was 3.85m1.

(2) The end-point was normal and the titre was 3.85m1. (3) The end-point was normal, but the titre was 4.04m1. Cal919m. Strontit, Barium. Maguesium._Sodium and Pdbaestal. Seven solutions were prepared containing (1) only bismuth, (2) 500mg. of calcium, (3) 500mg. of strontium, (4) 500mg. of barium, (5) 500mg. of magnesium, (6) 500mg. of sodium and C7) %Ong. of potassium. All seven solutions had identical end-points and titres of 3.85i1. Summarv. The following elements were shown to interfere uath the titration of bismuth and must be absent:- Mercury II, tin, iron III, indium, gallium, ceriUm4 thorlaum, titanium and eirconium.i The following elements were shown not to interfere and can be present in the amounts shown after each element. When the titre was altered by more than 0.03m1. the element was considered to interfere. The maximum amount tested for each element was %Vale. unless otherwise stated.

The titration was satisfactory in the presence of copper (1%3.), lead (500me.), mercury I (see note 1), thallium I (500mg.), ctl er (50ilme.), 1 • cadmium (500me.), antimo nr (1 mg. tellurium (Irv.), iron II (100ne. maxinnzu , amount tested, see note 2), aluminium Mame.), nickel (5ng.), cobalt (100mg. ✓ , maximum amount tested), zinc (5007113. ) 0 mangane✓se (lOng»), calcium t5OLVV:), , strontium t500mg:), barium (500mg.-)„ magnesium (5ille:), sodium (500mg.) and

potasiaum (50ang:). Liatat.

(1) it seems likely that mercury I does not interfere with the titration

and that the increase in titre observed in the Presence of 5031130 or mercury I was due to the presence of mercury II salts.

(2) The iron II was conplexed by ascorbic acid.

Comparisen S tbfp Fergep, frints tap can bje TAN:rated gar the GravimgDrec 14annitol.Phortheive spd oltieetrte. E•n•T•A. Methcele. Memento are coroidered to interfere if Deg. or less is the maximum mount that can be tolerated. The follewing elements interfere with both meth mercury, tellurium, selenium, Lees III s, indium, eeritun barium, titaniixt and zirconium. The foaming to nt rfere with the phoephate method but not the E.P.T.A• method ii Lead and iron

The follcwing elements interfere with the Et.D.T.A. method 1 phosphate method se Copper, nickel, gallitia and manganseee No teats were carried out on the phosphate °operation of biemuth from gallium bit it scene unlikely that moderate amounts of this element would interfere. In conclusion, it may be stated that the two methods are about equal. in selectivity and accuracy. The E.D.T.A. method is probably the most use— ful, firstly, be cauee the time required far analysis is less than with the phosphate method and seaway, because lead interferes with the phosphate method. Lead is nearly always present with bianuth in alloys and ores one its separation fral bismuth is one of the most difficult separations to per.

form. SECTION (A)

The Volatilisation of Bromides fran Perchloric-Emitobronic Acid . Solutions. Sane of the elements shown to interfere with the determination of biaer muth by the two methods investigated form lad-boiling point bromides. The volatilisation of these bromides could provide a separation of these clenents fran bienuth. The elements that this separation is likely to prove useful for are selenium, germanium, tin, arsenic, antimony, mercury arxi tellurium. The following table shows tie boiling points of some compounds of interest.

Element and Ccrnpound Volatilised. Boiling Point °C. Selenium, selenium tetrabranide 75 with decomposition. Gernanium, germanium tetrabronide 186 Tin, tin tetrabronide 202 Arsenic* arsenic tribrornide 221

Selenium, dieeleniun dibromicie 227 with decomposition. Antimony, antimony tribromide 280

Mercury, mercury dibromide 322 Tellurium, tellurian tetrabronide 1.21 Bismuth, bismuth tribromide 453 Sane elemente are probably volatilised as a mixture of compounds, e.g. selenium as selenium tetrabranide, diselenitvn dibranide all as selenium oxybroid.de. Fzcperimertal Mdhocl.

These experiments were carried out to gain qualitative information about the possibilityret obtaining separations. The elements or their oxides mere weieled, into a W./A. Phillips beaker ald 20m1i,of a, mixture of hydrabromic acid (9 volumes) and bromine (1 volume) were added.. Themixturewaswenued until dissolution was pieta and therilOtl, of perchlaric acid were added.. This solution was evaporated to fames of percbloric acid by heating the beaker on a thermo7 statically-controlled hot-plate. (The only thermostatically-controlled hot- plate that was available commercially was manufactured by Townsend and Mercer.. This hot-plate worked well and shaded an even distribution of temperature over its surface, but it was exceedingly difficult to service and element failures were rather frequent It was later replaced by a morn robust hot- plate manufactured by Toders.) The fuming was continued for five minutes, the solution allowed to cool, a 9n1. of the hydrobromic acid-branine mixture were added and the solution was again evaporated until fumes of perchlmic acid were evolved. The process was repeated mith a further 5m1. of the hydrobromic acid-bromine mixture. The temperature inside the beaker was determined by placing another beaker containing 10m1. of concentrated sulphuric acid and a thermometer on the hot-plate next to the test beaker. The results obtained at a temperature of 125±5!C. are shown in the tables..

Mement. Extent volatilised. Selenium (1) Completely (4).

Germanium Completely (4). Tin (2) , Completely (4). Arsenic Completely (4). Antimony (2) Completely (4). Mercury See note (5) Tellurium (3) See note (6) Bismuth See note (6)

(1)Red vapours were evolved during the evaporation and volatilisation appeared to be complete before perchlaric acid Amen were evolved. (2)When the perchloric acid first fumed, tin and antimony bromides separated as brown liquids that were later volatilised* (3)Tellurium formed a precipitate just before the lest of the hydrobranic acid was expeIled, but this redissolved when the perchloric acid fumed. (4)The perchioric acid solutions were diluted to loc.va. with water and saturated with hydrogen sulphide. No coloration or precipitate was formed. (5)The perchloric acid solution was diluted to 100m1. with water and saturated with hydrogen sulphide. A small mount of precipitate separated from the solution. 13y comparison with known amounts of mercury the anount of mercury remaining in the solution was estimated at 0.5mg. After four eve- perationswith hydrobromic acid, no mercury could be detected icy means of hydrogen sulphid e. (6)The perchlcric acid solutions were diluted to 100M1. with water and saturated with hydrogen sulphide* From the large amount of precipitate that was obtained it was evident that very little, if any, of these elements had been volatilised. Qualitative tests were nag carried out to see what temperature gave the best separation of bismuth fran tin and antimony. Tin anal antimony were chosen for investigation as they are the two elements most commonly associated with bismuth. -132

The most rapid evaporations that gave satisfactory volatilisation of tin and antimony were obtained at a temperature of 160-170°C. Above this temperature, the solution tends to bump badly and above 2000C., tin and antimony are precipitated as their hydrated oxides and are not completely volatilised. At temperatures below 115°C., antimony is not volatilised at a practical rate. As a result of these tests, the quantitative recovery of bismuth was investigated in the temperature range 120-170°C. The method used was as follows:- About 1.4g. of the bismuth were weighed into a 650-ml. Phillips beaker. The biamuth was dissolved by warming it with a mixture of 10m1. of hydrobromic acid and 2m1. of bromine. When, dissolution was complete, 10m1, of . perchloric acid were added and the solution was evaporated until fuses of perchloric acid were evolved. The beaker was heated on the thermostatically- controlled hot-plate at the temperature shown in the table. The solution was fumed for five minutes and then allowed to cool. To this solution were added 5m1. of hydrobronic acid and one drop of bromine and the solution was again evaporated until fumes of perchloric acid were evolved. The solution was fumed for five minutes and the process repeated with a further 5m1. of hydrobromic acid. This solution was cooled and 10m1. of diluted (14-1) nitric acid were added. The beaker was covered with a watch-glass, the solution heated to boiling and boiled to expel the bromine. The watch-glass was removed, the beaker was transferred to the hot-plate and the solution evaporated until fumes of perchloric acid were evolved. The solution was cooled, transferred to a 2501m1. volumetric flask and diluted to volume with water. A 50-ml. — 133

aliquot of the solution was transferred to a 650-ml. Phillips beaker and

diluted to 250711. with water. To the solution was added 0.2ml. of catechol violet indicator solution and the bismuth was titrated with E.D.T.A. solution

by the method given on page 62. The following results were obtained:- Temperature of Percentage of Biemuth Recovered. hot late

120-130 100.0 100.0 99.90 330-140 100.0 100.1 100.0

140.150 99.81 99.69 99.62 99.90 150-160 99.60 99.83 160-170 99.35 99.41 99.13 99.10 130-140 99.03 99.13 99.66 (see note below). The last three tests were carried out using a 400-m1. Phillips beaker in place of the 650-ml. beaker used for the other tests. In an attempt to confirm the recovery of bismuth at 130-140PC., the following three tests were carried outs- About 200mg. of bismuth were weighed into a 40-ml. Phillips beaker

and treated as described on page 132. The final perchloric acid solution was diluted with water and the bismuth was determined by the phosphate method described on pages 85 and 86. The WOentages of bismuth recovered were 99.52, 99.58 end 99.66. The only differences between these three tests andthosereported above was that the amount of bismuth had been reduced from 1.4g. to 0.2g. and that the bismuth had been determined by the phosphatemethod and not the E.D.T.A. method. As both methods of determining bismuth have been tested and shown

to give the same results, the percentage of bismuth volatilised must be a -134- function of the amount of bismuth present. The following results were obtained by the method given on page 132 with a hot-plate temperature of 125°C. Weight of Percentage of Di taken. Hi recovered. 49.59. 99.2 99.19mg. 99.7 248.0mg. 99.9 495.9mg. 99.9 The following results were obtained by the method given on page 132 with a hob-plate temperature of 130°C. Weight of Percentage of Hi taken. Bi recovered. 49.59mg. 51.0 49.59mg. 98.9 99.19ng. 99.6 99.19aig. 99.5 248.0mg. 99.7 248.0ag. 99.8 495.9 g. 99.8 495.9mg. 99.9 495.9mg. 100.0 It seened likel that the amount of bismuth volatilised might be affected by the presence of other elements. The type of effect might depend on whether or not the other element was volatile. Tests mere carried out in the presence of lead, cadmium or iron as examples of non-volatile elements and in the

-135..

presence of arsenic, selenium, tin or antimony as examples of volatile elements. As it was desired to have a readi17measurable loss of bismuth the amount of bismuth was fixed at 100Mg. and the hot-plate temperature at 125±5°C. .The following results were obtained:. lament rib, of added Percentage of added. element. Bi recovered. 99.4 99.5 99.6 Pb. 10 mg. 99.6 Pb. 50Cmg• 99.8 Pb. 5002g. 99.9 Pb. 1g. 99.9 Pb. lg. 100.0

Cd. 50 g. 99.9 Cd. 500ng. 99.8

Sn. 500ag. 99.6 Sn 5001g. 99.6

Sb. Wang. 99.6 Sb. 500Tig. 99.6

As. 99.6

500mg. 99.6 - 136 -

loon. 99.9 Fe. LOQng. 100.0 When the volatilisation procedure was carried out in the presence of iron, it was noticed that bromine was freely evolved just before the perchloric acid began to fume. This evolution of bromine did not usually occur and therefore, the following teats were carried out to see whether the destruction of the bromide affected the volatilisation of tin and antintomr. Into a 650-m1.. Phillips beaker were weighed 100mg. of iron powder and this was dissolved in lOnl. of a mixture of hydrobromic acid (9 volumes) and bromine (1 volume). When dissolution was casplete, 10m1. of perchloric acid were added and the solution was 'evaporated on the hot-plate at 125±50C. The evolution of bromine was again observed just before the perchloric acid fuiied.

The above experiment was repeated with 9ig.• lOng* and 501g. of iron. The decomposition of the hydrobranic acid was appreciable even with only 5mg. of iron present.

The above three experiments were repeated with 100mg. of antimony present After three evaporations with hydrobromic acid as is described on page 132, large amanita of antimony were still present in the solutions containing 10mg. and 5Osg. of iron and a small amount was still present in the solution containing 5rsg. of iron. The presence of antimony could easily be detected t the white precipitate of hydrated antimony oxide that separated during the fuming of the perchloric acid. One of the precipitates was filtered and washed and the presence of antimony was sham by dissolving it in hydrochloric acid, diluting the solution with water and saturating it with hydrogen sulphide - antimony sulphide was precipitated. - 13? -

Thus, iron causes the decomposition of the hydrobromic acid and this prevents the volatilisation of antimony. If iron was converted into a conplex with phosphoric acid, it seemed likely that the oxidation of the hydrobromic acid would be prevented. Therefore, the following tests were made in the presence of phosphoric acid. Into a 650-ml. Phillipe beaker were weighed 250mg. of antimony and 100mg. of iron powder; these were dissolved in 10a. of a mixture of hydrobromic acid (9 volumes) and bromine (1 volume). When dissolution was complete, 10m1. of perchloric acid and 0.2m1. of syrupy phosphoric acid were added and the solution wan evaporated on the hot-plate at 125±5°C. The solution was cooled, 5m1. more of hydrobronic,acid were added and the solution was again evaporated to fumes of perohloric acid. The process was repeated with a further 9111. of hydrobromic acid. The destruction of the hydrobromic acid was not observed and the antimony MB completely volatilised, as shown by diluting the solution with water and saturating it with hydrogen sulphide. When the above experiment was repeated with 250ng. of iron the hydrobromic acid was again destroyed and the antimony was not volatilised. then thin experiment was repeated and the phosphoric acid was increased to 0.9n1., the antimony was volatilised and no decomposition of the hydrobronic acid was observed. Thus, the optimum.conditions for the separation of selenium, germanium, tin, arsenic, antimony and mercury tram bismuth by volatilisation of the other elements as bromides are as follows:- (1) The use of a 650-mi. Phillips beaker made of Pyrex glass. A smaller beaker can lead to loss by presenting a smaller surface for condensation. (2) The use of a liquid temperature inside the beaker of 125±5°C. for the evaporation of the volatile bromides.

(3) The use of not less than 10ml.ef 60 per cent. perchlotic acid to ensure the non-volatilisation of bismuth bromide.

(4) Avoidance of the prolonged fuming of the perchloric acid. (5) The use of not lesa than 50Qtg. of bismuth. With increasing amounts of other non-volatile elements present, the amount of'bismuth taken can eafelo, be reduced to less than 50O g. The amount of bismuth volatilised is nearer to iraconstant weight than to a constant per centage.

(6) The addition of le. of diluted (1+ 9) phosphoric acid for every 10Cmg. of iron that are present* (7) The use in the fume cupboard of a.draught that is strong enough to remove all the fuses up the duet, but is not so strong as to cool the sides of the beaker too much. When a mixture of 10m1. of perchloric acid and 10ml. of hydrobronic acid is evaporated in a 650-ml. Philips beaker with a liquid temperature of 12515°C. Tunes of perchloric acid should be evolved after about 45 minutes heating. The final method of carrying out this separation is given below. Weigh the sample (to contain 500mg. or more of bienuth)'into a 650-ml. Phillips beaker, add 10m1. of a mixture of hydrobranic acid (9 volumes) and bromine (1 volume) and warm the covered beaker to' help in attacking the Sample. Add mere bromine cif necessary) to effect the dissolution of the sample. When the sample has dissolved, remove the cover, add 10m1. of perchloric acid and ]ml. of diluted (1+ 9) phosphoric acid for every 10Cmg. of iron present.

Transfer the beaker to the thermostatically-controlled hot-plate and evaporate the solution with the liquid temperature inside the beaker at I2515°C. When perchioric acid fumes are evolved, heat the beaker for a further two or three, minutes. Cool the solution and add 5m1. of the hydrobronic acid- bromine mixture and repeat the evaporation and fuming as before. If large mounts of volatile elements are present, and especially if they include antimony and mercury, re-treat with a Ibrther 5m1. of the hydrobromic acid- brarine mixture. Provided the above procedure is adhered to selenium, germanium, tin, arsenic, antimony and mercury can be completely volatilised and bismuth will be quantitatively retained in the perchloric acid solution. Preci4tation qt Bismuth by Mon Ilvdroeen SuloWe. As bismuth can be separated from many other elements by precipitation by hydrogen sulphide from acid solutions, the range of acid concentrations aver which bismuth can be quantitatively precipitated was determined. In each test 121. of a solution containing l(ng. of bismuth was diluted to lAml. with acid of the given concentration, heated to 60°C., saturated with hydrogen sulphide, cooled and again saturated with hydrogen sulphide. The precipitate obtained by this method was heavy and black in colour. The precipitate settled quickly to leave the supernatent liquid clear. The precipitate was filtered, the filtrate nearly neutralised with diluted (14-1) aqueous ammonia (the solution was left about 0.5N•with respect to free acid) and the solution again saturated with hydrogen sulphide. If no coloration or precipitate was formed it was assumed that precipitation had been complete at the higher acid concentration. The following conclusions werereacheds- (1) For the complete precipitation of bismuth sulphide, the concentration of free hydrochloric acid should not exceed three normal. In solutions four -140

normal with respect to free hydrochloric acid, no precipitation occurs at 60°C. and precipitation is far from complete at roan temperature. In solutions six normal with respect to free hydrochloric acid, no precipitate is firmed from either hot or cold solutions. (2)Bismuth sulphide is quantitatively precipitated from solutions that are eighteen normal with respect to free sulphuric acid. Precipitations from solutions containing larger enounta of sulphuric acid were not investigated, as the nature of the solutions prevents any practical applications. (3) Bismuth sulphide is readily' soluble in hot 2N-nitric acid, (1,) Bismuth sulphide is quantitatively precipitated fran ammoniacal-tartrate solutions. Ten millilitres of the ammoniacal-tartrate solution contained lOng, of bismuth, Sang. of tartaric acid and 1ml, of diluted CL+ 1) aqueous ammonia in excess of that needed to neutralise the solution to methyl red. In order to test the filtrate for bismuth, it was evaporated to a snail volume and 1m1. of sulphuric acid was added. The evaporation was continued until the organic matter began to char, the carbon was oxidised by the careful addition of '100-volume' hydrogen peroxide solution and the clear solution heated until fumes of sulphuric acid were freely evolved. This solution was cooled, diluted to lOni. with water And saturated with hydrogen sulphide.

No precipitate or coloration was produced. Although sulphide precipitations are easily made and the precipitate is easy to filter and wash, the process is rather unpleasant to use. The worst feature, however, of sulphide separations is the dissolution of the precipitate. This nearly always leads to the formation of a bead of sulphur that is difficult to free from occluded sulphides. The dissolution in an oxidising acid must lead to the formation of some sulphate ion and this may be a nuisance in the subsequent analysis.. If lead is also present, same of it will be precipitated and this is likely to lead to losses of bismuth when the unattacked sulphur is filtered off. For these reasons, it was decided to investigate the cementation of bismuth on zinc powder as a substitute for precipitation by hydrogen sulphide. The_Cementatlap sr 84piptil on Zinc Powder. The general scheme of analysis that was neat beginning to develop was attack of the sample with a mixture of hydrobromic acid, bromine and perchloric acid, and evaporation of the solution to fumes of perchloric acid to expel volatile bromides. The remaining bromides would then be destroyed by adding nitric acid and evaporating the solution until fumes of perehloric acidwere evolved. Thus, a solution of the sample in perchloric acid would be obtained. Apart from any unattacked sample, the solid residue remaining after dilution of the solution with water is likely to contain compounds such as lead sulphate, bismuth sulphate and bismuth phosphate that are insolUble'in perchloric acid. As most of these compounds are soluble in hydrochloric acid, the use of this acid is to be preferred. The solution now contains about 100m1. of normal perchloric acid.. In fact, the amountof acid present will be less than this by the amount that was volatilised during the evaporations and by the anount required to convert the soluble salts to perchlorates, The addition of 5g. of sodium chloride would effectively convert this acid to hydrochloric acid. When zinc is added to the solution to precipitate the bismuth, the final acidity after precipitation should be loci in order to obtain the complete precipitation of bismuth. The amount of zinc required to neutralise 100m1. of normal acid is about three grams. If three grams of zinc are used.and a final volume of 250m1. and a final acidity of 0.1N are chosen, then an additional 2931. of normal acid will be required. These calculations are only approximate for many reasons, e.g. the zinc powder will contain zinc oxide, same zinc will be consumed in precipitating the bismuth and the amount or acid lost in the evaporations will vary as will the amount and nature of the soluble salts. However, these calculations provide a starting point for the investigation of the cementationvf bismuth on zinc powder. The following method was tested and is based on the general considera- tions outlined above. Into a 500-ml. conical flask were weighed 250mg. of bismuth oxychloride (200mg. of bismuth) and this was dissolved in 2m1. of hydrochloric acid. To this solution were added Uhl. of 60 per cent. wfw. perchioric acid'and 5g. of sodium chloride.. The solution was diluted to 20031. with water and heated to 40-50°C. Three grams of Anai,aR zinc powder were weighed on to a watch-glass. The zinc powder was added to the bismuth solution in small portions over a period of about five minutes (0.1-0.2g. of the zinc powder was retained on the watch. glass), The solution was then heated to boiling and maintained at this temperatumumtil the evolution of hydrogen ceased. The retained portion of the zinc powder was added and the solution cooled by imersing the flask in running cold water. The precipitated metal was filtered on a 9-cm. No.41 Whatman filter-paper that had been dusted with about 5Llng. of zinc powder. The metal was washed with cold water. — 143

The filtrate was tested for bismuth by saturating it with hydrogen.

bide. No bienuth .was detected. 13y comparieon with know mounts of biantith it was shaern that lees than 0.1mg. of bienuth was present. The above te$t was repeated with 2211. of hydrochloric acid. and no perchloric acid or sodium chloride. No bisnuth way detected in the 'filtrate. The separation of bienuth from various other elements wg.la now investi— gated the method described above being used. The amount of the other ele— ment taken was 250sg. li,rhen necessary, the material weighed was dissolved in nitric acid and the solution evaporated with perchloric acid to expel the nitric acid. When the material was soluble in perchloric acids it was dissolved in perchloric acid and the solution evaporated until ft1105 of per— chloric acid were evolved. The source of the element is shoan in brackete after the element in the following table aeent. eight in ppt. Weight in filtrate.

Pb (Pb0) 250ig. (1) Less than 0.1118* (2) Cu (qu)- 25O' g. (1) Lees than 0.1mg. (2)

(F) 25Ong. (1) Lose than 0.1mg. (2) .00 (Na2Sett3) 25. (1) Less than 0.1mg. (3) •

Te (To) 25'43g. (1) Less than Ging (3)

Ag (A00 ) 25Ong. (4) Less than 0.1ng. (2) Fe (Fe) LOS3 than 0.2mg. (5) 25ang. (1) Al (Al) Less than 0.2mg. (5) 25Cong. (1) Cr (Cr) Lexs than 0.2mg. (5) 25Chg. (1) 30 (3eCO3.41120) Less than 0.2ig. (5) 25Cmg. (1) U (U32(NO3)2.61/20) Less than O.]ig. (6) 25thig. (1) Ti (Ti(SO4)2) Less than O.2ng. (5) 25011g. (1) Zr (Zr(NO3)4) Less than O.2ng. (5) 250ng. (1) Th (Th0,103 ) Less than O.2ng. (5) 25Ong. (1) co (co(NO3)4.2NE No3) Less than 0.2mg. (5) 25thtg. (1) Mn (41102) Less than 0.1mg. (7) 250/1g. (1) Co (Co) Less than 1mg. (8) 250ng. (1) Ni (Ni) Less than log. (8) 250ng. (1) Tl (T11103) Less than lmg. (8) 250ng. (1) Ca (CaCO3) Less than 0.1mg. (9) 250mg. (1) Mg (i1g) Less than 0.1mg. (10) 250 g. (1) Mo (4203) Less than 0.1mg. (a) 100mg. (12) (1)The values were assumed by difference. (2)The filtrates were saturated with hydrogen sulphide. (3)To 65m1. of the filtrate contained in a Nessler cylinder were added 35m1. of hydrochloric acid and the solution was saturated with sulphur dioxide. (4)The silver was mostly precipitated as silver chloride before the sine powder was added, (5)To the precipitate was added a mixture of 10m1. of 2M4hydrochloric acid and sufficient bromine to dissolve the metal. The solution was heated to boiling and boiled to expel the excess of bromine. The solution was saturated with hydrogen sulphides cooled and again saturated with hydrogen sulphide . The precipitate was filtered, the filtrate was heated to boiling, and the solution was boiled to expel the excess of hydrogen sulphide. To this eau tion was added a drop of bromine and the solution heated to boiling and boiled to expel the excess of bromine. - 145 -

The solution was cooled, 1 drop of methyl red solution was added followed by diluted (14-1) aqueous amonia until the solution was neutral to the indicator. After heating to boiling, the solution was set aside for ten mixmtes. In all tests 0.2ig. of the elenents could be clearly seen. (6)The bismuth was removed as described in the first paragraph of note (5). The solution was cooled and solid ammonium acetate was added to raise the pH to about five (the solution was tested with universal indicator papers). To this solution were added 2ml. of a. saturated solution of potassium ferro— cyanide in water; in the presence of ,uranium, a brown coloration or preci— pitate was formed. By comparison with known amounts of uranium, it was shown that 0.1mg. of uranium could be detected. (7)The bismuth was separated as described in the first paragraph of note (5). To this solution, contained in a 150-mi. beaker, was added ]ml. of sulphuric acid and the solution evaporated until fumes of sulphuric acid were freely evolved. The sides of the beaker were washed darn with water and the solution again evaporated until fumes of sulphuric acid were evolved. To this solution were added 100m1i of water, 10W1. of nitric acid and 0.1g. of solid potassium pertodate. The solution was boiled to develop the colour of the permanganate ion. By comparison with known amounts of manganese, it was shown that 0.]mg. of manganese could be detected. (8)The bismuth was separated by the method described in the first paragraph of note (5). The solution was cooled, made ammoniacal by the addition of diluted (1+ 1) aqueous ammonia and saturated with hydrogen sulphide. The coloration or precipitate wascompared.with solutions containing known amounts w146 -

of the element being estimated. (9)The bismuth was separated bar the method described in the first paragraph of note (5). The pH of the solution was adjusted to twelve or greater by the addition of 5N-sodium hydroxide solution (the pH of the solution was tested on a drop-reaction tile by means of B.P.H. '1014' indicator). To this eolation was added sufficient solid murexide to colour the solution. In the absence of calcium, the colour of the solution was violet but in the presence of O.]mg. of calcium, it was pink. The addition of E.D.T.A. solution changed the colour back to violet.. (10)The bismuth was separated by the method described in the first paragraph of note (5). The solution was neutralised to litmus paper by the addition of 5N-nodium,hydroxide solution and 1ml. of the eemonia-anmonium chloride buffer solution (see page 61) was added. To this solution was added sufficient solid Sao Chrome Black T to colour the solution. In the absence of magnesium, the colour of the solution was pure blue and in the presence of 0.1mg. of magnesium it was magenta. The addition of E.D.T.A. solution changed the colour back to pure blue. (11)The precipitate was dissolved in 101111. of.diluted (1A-1) nitric, acid, to this volution was added hi].. of sulphuric acid _and the solution evaporated until fumes of sulphuric acid were evolved. The sides of the beaker were washed awn with water and the solution again evaporated until fumes of sulphuric acid were evolved. No blue colour was developed on fuming the acid. By caparison with known amounts of molYbderum it was shown that 0.1mg. of molybdenum could be detected. (12)The value was seemed by difference. Only 100mg. of molybdenum were taken. - 147 -

When bismuth was precipitated in the presence of iron, it wee observed that the precipitate, instead of being grey in colour as was usual, was This precipitate was much easier to filter, wash and dissolve than was the grey precipitate ,obtained in the absence of iron. A qualitative test (the metal was dissolved in diluted (1+ 1) nitric acids the solution evaporated to dryness, the residue dissolved in diluted (1+ 9) hydrochloric acid and a solution of potassium ferrocyanide in diluted (1+ 9) hydrochloric acid was .added ,zinc was precipitated as zinc ferrocyanide) showed that very much less zinc was present in the precipitate obtained in the presence of iron. The precipitation in the presence of iron was.repeated with 51g., lOng. and 50mg. of iron. The black form of the precipitate was obtained in the presence of 3i)ng. and 50mg. of iron. Three precipitations were carried out in the presence of 20mg. of iron, but this time all the zinc powder was added before the solution was heated to boiling. No zinc was added after the solution had been boiled as it was desired to test the precipitates for zinc to see if the amount of zinc re— maining was constant. For thin same reason the filter paper was not dusted with zing powder. The precipitates were examined for zinc by the method, described above. The amount of zinc present in the three precipitates varied between wide limits. It was also observed that the precipitates that con— tained the most.zinc had been the most persistent in liberating hydrogen during the digestion of the precipitates. In an attempt to obtain more uniforn. dissolution of the zinc, the following modification of the method was tested. Into a 650.1m1. Phillips beaker were weighed 250mg. of bie-mth oxychloride and this was dissolved in 12m1. of hydrochloric acid. To this solution wan - 148 -

added 1ml. of a solution containing 201g. of iron. Three grams of AnalaR zinc powder were weighed on to a watch-glass:. The bismuth solution was diluted to 50m1. with water, heated to boiling and the zinc powder added in small portions at a time (0.1-0.2g. of the zinc powder was retained on the watch-glass). The precipitate was digested at the boiling point of the solution until the evolution of hydrogen ceased. The solution, was diluted to 200n1., with water, the remainder of the zinc powder was added and the solution heated to boiling. The solution was cooled by immersing the beaker in cold ruining water. The cooled solution was filtered through a 9-cm. Noal Whatman filt6r. paper that had been dusted with about 5Gng. of zinc powder. The precipitate was washed with cold water. The filtrates were saturated with hydrogen sulphide and no bismuth could be detected. Three precipitates were obtained by the above method (except that all the zinc was added before the solution was diluted to 2CX)nl. and no zinc was added to the filter paper) and tested for zinc as before. The zinc contents of the precipitates were lower and much more uniform than before. In order to investigate the amount of hydrochloric acid that could be Used and the amount of bismuth that could be precipitated, tests were carried out using the method given above. The results are smenarized in the follow- ling table:- Volume of Weight of Amount of hydrochloric bismuth taken. bismuth in acid added. the filtrate. 12001. of 1N 2OQng. Less than 0.1mg. 1411. of 1N 20C►ng. Less than 0.1mg. 149 -

16011. of ,1N 200ng. Less than 0.1ms. 120s1. of IN 500mg. Less than 0.1mg. 140111. of 1N ,500mg. Less than 0.1mg. 1607110 of 1N 500mg. About 0.1mg. 120M1. of 1N, lg. About 2ng. 140ml of IN lg. Large amount. 3.60ra. of IN lg. Large amount. The bismuth in the filtrates was estimated by saturating them with hydrogen sulphide* Thus, the' free acid content of the solution should be between 120 and 150m1. of normal acid and the total amount, of bismuth present should not exceed 500mg, In the application of the method given on pages 147 and 148 to the analysis of ores, some ores gave solutions from which it was impossible to obtain complete precipitation of the bismuth. Qualitative analysis of these ores showed the presence of tungsten and molybdenum. These elements are not found inmost bismuth ores. It was assumed that, because of the many valency states that these elements can show, they catalysed cone sort of oxidation of the bismuth metal; possibly by preventing the complete reduction of. the iron to the fermis state. Thus, it was decided to try adding ascorbic acid to reduce and form a cosploax with the iron. Complete precipitation of the bismuth was obtained in the presence of ascorbic acid. The method finally adopted is given below:- Prepare 50m1. of a solution containing not more than 5001g. of elements that can be precipitated by zinc powder and between 120 and 150m1. of normal 15© - acid. If the acid present is sulphuric, or perchloric acid, add 5g. of sodium chloride. To the solution add 1ml. of a solution containing 20.

of, iron (moisten 10g. of ferric chloride hexahydratewithIml. of hydro-- chloric.acid, add water to dissolve the solid and dilute the solution to 100m1. with water). Weigh 3g. of AnalaR zinc powder on to a watch-glass. Heat the solution to boiling and add solid ascorbic acid in small quantities at a time until the yellow colour of the ferric chloride complex is bleached. Then add the zinc powder in small portions at a time to the covered beaker, but retain about 0.1g. of the zinc powder on the watch-glass. Remove and wash the cover, wash down the sides of the beaker with a Small volume of water and heat the solution at the boiling-point until hydrogen evolution ceases. The beaker should not be covered during this period as the access of air pro- motes the dissolution of the excess of zinc. Add 150m1. of water and heat the solution, to boiling. Add the remainder of the zinc powder and about 0.2g. of ascorbic acid. Cool the beaker in cold running water. If hydrogen evolution ceases during the cooling, add another few milli gsms of zinc powder« When, the solution is cold, filter the metal on a 9-cm. No.41 Whabnan filter-paper that has been dusted with about 50mg. of zinc powder. Waah the precipitate and paper with cold water. ggMMACto Bismuth can be quantitatively precipitated by zinc powder under the conditions given;- lead, copper, mercury, selenium, tellurium and silver are also quantitatively precipitated. Bismuth can be separated from mcaybdenum, iron, aluminium, chromium, beryllium, uranium, titanium, zirconium, thorium, cerium, manganese, calcium and magnesium. The separation from cobalt, nickel and thallium is not so good. This is also true of separations based on precipitation by hydrogen sulphide. 151

The Pcaptipitetion of Bismuth Oxvbromile. The method published by Moser and Maxymowicz(270) in, according to Hillebrand et al., as follows:- "Prepare a nitric acid solution, and slowly add sodium carbonate sau- tion until the precipitate dissolves with extreme difficulty. Dilute to 200 to 30Cml., add 2g. of solid pobasstin or sodium bromate, and heat to boiling. If the turbidity which arises does not clear up on boiling, add nitric acid dropwise until it does, To the boiling solution add a 10 per cent. solution of potassium or sodium bromide dropwise from a pipette until a turbidity ensues and the solution is deep brown in colour. Cover with a cover glass, boil until the solution is clear yellow, add a little more bromide, and repeat until no further precipitation takes place, even on the addition of a few drops of bromate solutionl and then boil out all of the bromine. Let settle, filter, and wash with hot water." Aliquots of the standard bismuth solution were transferred to 400-mli beakers, the solutions were diluted to 100m1. with water and the bismuth was precipitated by the above method. The precipitates were filtered on sin.. tered-glass crucibles, washed with hot water and dried at 110°C.; they ware constant in weight after two hours drying and were not hygroscopic* The aliquots measured contained 0,1054g. of bismuth which is equivalent to 0.1537g. of bismuth oxybromide. The weights of bismuth oxybrornide found were 0.1495g., 0.1495g. and 0.1497g., no bismuth could be detected in the filtrates by saturating them with hydrogen sulphide. By comparison with known amounts of bismuth the limit of detection of this test was shown to be 0.1mg. of bismuth in the total filtrate and washings. These results are — 152 — about 2.8 per cent. lower than the theoretical result; therefore, bismuth oxybremide, when precipitated by this method, is unsatisfactory as a weighing form in spite of the good reproducibility obtained in the replicate deter— minations.

Before work was started on separations by means of the oxvbranide method it was decided. to modify the method of precipitation for the following reasons. (1) If the solution was neutralised in the manner recommended, a permanent precipitate was formed on the addition Of the solid potassium bromate. This could only be dissolved by the addition of several millilitres of nitric acid, which considerably increased the mount of potassium bromide solution that had tc, be added and consequently the amount of bromine that was liberated. (2) After most of the bromine had been expelled by boiling, the solution sometimes bumped, which made the removal of the last of the bromine difficult. (3) The authors state that the bromide solution is added until no further precipitation of bismuth occurs; in practice, it is almost impossible to detect this point. If the bromide solution .is added until no more bromine is liberated this difficulty does not arise, but in separations this will. cause an unnecessary increase in the pdd of the solution, as precipitation appears to be complete before the solution is neutral: The exact ,point at which precipitation is complete is difficult to detect because of the colour of the solution, and the fact that the precipitation is not instantaneous especially when the bismuth concentration is very low.

If branide•-bramate is added until no further bromine is liberated the pH of the cooled solution was found to be about 6.3. This means that if metals such as lead are present they will be precipitated, at least in part, — 153 • as hydroxides. The following method was found to be more convenient.

(a) Realents. Potaeapo HrpmA/eSolutior). Dissolve 2g. of potassiun bromide in 10 1. of water and filter the solution. Nixed Indicator,Solution. Dieeclve 0.1g. of methyl orange and 0.25g. of indigo carmine in 100m1. of water. The indicator colour changes from violet in acid solution through a neutral grey colour at pH 4.0 to green in alkaline solution.

Sodium Acetat, Solution. Dissolve 10g. of the anhydrous salt in 100m1. of water and filter the. solution. Ammonium Acetate Solution B.P. This solution contains 57.5 per cent. w/v. of ammonium acetate and was purchased from Napkin and Williams. Ltd. The solution was filtered before use.

(b) 1!cthod. Prepare 100m1. of a solution containing not more than 250mg. of bismuth and between 1 and 3111. of nitric acid' Heat the solution to the boiling point and add, drop by drop, with continuous stirring of the solutions .10m1.. of potassium bromides solution. Dilute the solution with 200m1. of hot water containing lg. of potassium bromide. Heat the solution to the boiling point, add 6 to 10 drops of the mixed indicator solution and either sodium or ammon— ium acetate solution until the colour of the indicator is grey to greenish grey* Digest the precipitate at the boiling point of the solution for 15 - 154 -

minutes. Filter the precipitate on a 9-cm. No.I2 Whatman filter paper and wash the precipitate and paper with warm water.

E2121., (1) The amount of potassium bromide added does not seem to be important. Complete precipitation of the bismuth was obtained in the presence of 0.5

to 5.0g. of potassium bromide.

(2) Bruno-phenol blue was originally used as indicator, but the mixed indicator is preferred because of the closer control of the pH that is possible.

(3) Ammonium acetate has been used in the tests described in the following pages. The volume of ammonium acetate solution that is required in usually between 3 and 5m1. Neutralisation by sodium acetate was compared with neutralisation by ammonium acetate for the separation of bismuth from lead, copper

and cadmium. The results are given in the table on page 159.

(4) The bismuth in the combined filtrates and washings was estimated by adding 25m1. of nitric acid and sufficient bromine water to decolourise the indicator. This solution was diluted to 500n1. with water and 100m1. transferred to a Nessler cylinder and the bismuth estimated as is described on page 60. The amount of bismuth found in the filtrates was between 0.02 and

0.03mg.

(5) Bismuth ceObromide, when precipitated by this modified method, is still tutsatiefactory as a weighing form. This can be seen from the first figures

in the tables on pages 157 and 159. The results are 3.6 .per cent. lower than the theoretical resat, however, the precision remains good. In the tests so arises in the following table the bianuth was precipi.►

tated by the method given on page 153, the neutralisation being made with ammonium acetate solution. The methods used for the estimation of the 155

occlud 'visas in the precipitates were for most elements identical with those described for the bismuth phosphate precipitates. Where this is so, a reference is given to the page =which the method is described. The eources of the other elements are the sane as is described under the separation of the elements by the phosphate method. The amount of bismuth tdsen was 250mg. Element Amount Amount Method of determining element in precipitate. Added. Added. in ppt. Ag. Quantitatively precipitated. 100mg. 0.05mg. As for bismuth phosphate. See pages 89-90. T1. 250mg. 0.1mg. As for bismuth phosphate. See pages 89-90. Tl. 500mg. 0.2mg. As for bismuth phosphate. See pages 89-90. Pb. 100vg. Nil. By weighing the precipitate as described in note 1., Pb. 250ng. 1.3ng, As above. Pb. • 500mg. 2.911g. As above. Pb. img. Osaing. PolarograPhibally. As described in note 2. Pb 0.6ng. As above. Pb. 100mg. 0.', g. As above. Pb. 25Ong. Wog. As above. Pb. 500ng. 0.97mg. As above. Pb. 500ng. 2.6mg. As ,above. Pb. 500mg. 3.2mg. As above. Hg 100mg. 0,1mg. As for bistuth.phosphate. See page 92. 0g. 250mg. 0.1mg. An above. Hg. 500mg. 0.15ng. As above. 156

5001tg. 0.19 mg. As for bismuth phosphate. Zee pages 92-93. Cu. Inge 0.005mg Po1arograpbicai1'. As described in note 2, Cu. 5Ong 0.05mg. As above. Cu. 25Ong 0.08mg. As above. Cu, 500mg. 0.00mg. As above. Cd. 100mg. 1i1. By weighing "the precipitate as described in note 3. Cd, 250mg. 0.3mg As above. Cd. 500mg. (Lang. As above. Cd. 0.004mg. Polerographically as described in note 2. Cd. 50mg. loam& As above. Cd. 250mg. 0.1mg. As above. Cd. 500mg 0.1eng. As above. Se. 50mg. 0.5mg. Colorimmtrically as for bismuth phosphate. See page 95. 1.1mg. Gravimetriceily as for birth phosphate. See page 95. Se. 250mg. 2.6mg. As above. Te. 50mg. (Lang. Colorimetrically as for bismuth phosphate. See page 96. Te. 100 g. 0.3ng. As above, Te„ 250m„ 0.4mg. As above. Fe, Quantitatively precipitated. Al. Partially precipitated. Be 50mg.. 0,210. As for bismuth phosphate. See page 100. Ca. Quantitatively precipitated. Th. «» Quantitatively precipitated. -157—

Ti. Quantitatively precipitated. Zr. Quantitatively' precipitated. Zn. 500mg. 0.08mg. Ac for bismuth phosphate. See page 101. Ni. 500 g. 0.051 g. As for bismuth phosphate. See pages 3.01-102. Co. 50Ong. 0.05ng. As for binnuth phosphate. See page 102. 20ng. 5.4mg. Ao for bismuth phosphate. .See pages 103-104. 250 mg 12m g. As above. Mb: 500mg. 1Bmg. As above. 1g 250mg; 0.3mg. As for bienuth phosphate. See pages 104405. Ca. 250mg. Oamg. As forbienuth phosphate. See page 105. Sr. 250ng 0.1mg. As for bienuth phosphate. See page 105. Ba, 250mg. 0.1mg. As for bienuth phosphate. See page 105. Maas (1)The bismuth was precipitated as is described on page 153 and the precipitates were filtered on porous-based porcelain crucibles, washed with hot water and dried at 110°C. The following results were obtained. Weight of Weight of Calculated Weight of Bi taken, Pb taken. Wt of Mar. Bi0Br found. 0.2483g. Nil. 0.3622g. 0.3492g• 0.2483g• 100mg. 0.3622g. 0.3492g. 0. 243g• 250mg. 0.36228, 0.3516g. 0.2483g. 500mg. 0.3622g. 0.3544g. Th'e weight of lead present in the precipitates WAS C ulated assuming the lead was coprecipitatnd as lead bran:Lie. (2)The precipitate and paper were dried in the oven at 105°C. and the precipitate was detached from the paper and collected in a 100-m1. beaker. 158-

It was diesolved in 2m1. of hydrobromic acid and the solUtion was evaporated to dryness by placing the beaker on a sand-bath. Menthe residue was dri, the beaker was buried in the sand to a depth of about 3cm. (the sand-bath was adjusted so that a thermometer buried in the sand indicated a temperature of about 300°C.). During this period of heating yellow fumes of bismuth tribromide mere evolved. when this evolution ceamed, the beaker 'feat raved from the sand-bath and the sides of the beaker were brushed with the flame of a fish-tail burner to volatilise condensed bismuth tribromides The beaker MB aliened to cool and the residue was dissolved in 0.5m1. of hydrobrornic acid. The solution was evaporated to dryness and the bismuth tribromide volatilised as before. The residue was re-treated with a further 0 5m1. of hydrobromic acid. To the cooled beaker were added .2m14 of'nitric acid and 1ml. of diluted (14-9) perchloric acid. The solution was evaporated until fumes of perchioric acid were evolved. This solution was diluted to a suitable volume in 1M -hydrochloric acid containing 0.005 per cent. of gelatin and the derivative polarogram was recorded by means of a Cambridge Instrument Conpanyie pen recording polarograph fitted with a Univector unit. The standards were prepared by dissolving pure bismuth oxide in hydro- bramic acid, adding known mounts of the other elements and then treating the solution as is described for the precipitates. A blank determination was carried out on the bienuth oxide and the reagents. (3) The bismuth was precipitated as is described on page 153 and the precipitates were filtered on poroue-based porcelain crucibles, washed math hot water and dried at 110°C. The following results were obtained. 159 4.

Vieight of Weight of Calculated. Weight of Bi taken. Cd taken. Wt of BiOnr. 01.03r found. 0.2483g.' 0.3622g. 0.3492g. 0.2483g. 100mg. 0.3622g. 0.3491g. 0.2483g. 25011g. 0.3622g. 0.309g4 0.2463g. 500mg. 0.3622g. 0.3511g. The weight of cadmium present in the precipitates was calculated assuming the cadmium was coprecipitated as cadmium bromide. The separation of bismuth froM copper,-lead and cadmium obtained when the solution was neutralised with ammonium acetate was compared uith the separation obtained When the solution was neutralised with sodium acetate. The amounts of copper,' lead and cadmium in the precipitates were determined by the polarographic method described on. pages 157 and 158. The reduction waves due to copper, lead and cadmium were recorded on the sate polarogran. In the following tests 250mg. of bismuth and 500mg. of copper, lead and cadmium were taken.- Neutralising Salt.- Coprecipitated Cu. Coprecipitated Pb. Coprecipitated Cd. Ammonium acetate. 0.10ng. 1.0mg. 0.6mg Ammonium acetate. .0.0Emg. Zang. 0.4mg. Ammonium acetate.. 0.08mg. 1.4mg. 0.9ng•

Sodium acetate. 0.10mg. 2.6mg. 0.6mg. Sodium acetate. 0.12ng. 2.9tg. 0.5mg. Sodium acetate. 0.10Mg. 2,2mg. 0.6mg. Thus, there seems to be little to choose between the Womethode or neutral cation. In all subsequent work with the oxybremide method, the neutralise- tionwas made with a solution of ammonium acetate. 160 -

StrImary of the Slparatione that are Possible by the Oxybromide !lethal. A single precipitation gives a separation from the following elenente present in amounts up to the amount shown in brackets after each element. An element is considered to be separated if not more than0.2mg. is copreci- , pitated with the bismuth« Thellium(500mg.), lead(5mg.), cOPPert5OCVng. maxi- , mum amount tested), meraary(50Jmg. maximum amount tented), cadmium(25Ong.), ? 2 selenium(2( .), tellurium(100mg.), sinc(50Ong. maximum amount tested), nickel Mame. maximum amount, tested), cobalt(500ng. maximum amount tested), meg- nesiii:n (n(x. maximum amount tested), calcinm(250mg. maximum amount tested), strontium(250mg. maxiTexn amount tested) and! barium(250mg. maximum amount tested). One diva' vantage of this method is that although it may give a separation from two other elements when only one is present at a time, it may not give a separation from either when they are present together. Thus, using this method it is possible to separate bismuth from copper and bismuth fray tellurium, but not bismuth from copper and tellurium. This is because copper tellu- rite is precipitated with the bismuth oxybromide. Therefore, when the separation is applied it should be to separate bienuth from a mixture of cations, or a mixture of anions, but not a mixture of cations and anions unless the particular combination has been tested and the separation shown to be satisfactory.

Other Separations that may' be. Necessary, in tilt General Scheme of Analysis. The following is the scheme of analysis:- (1)Volatilisation of the bromides of eolenium, germanium, tin, arsenic, antimony and mercury. (2)The separation of bismuth as metal from molybdenum, iron, aluminium, -1.61 -

chromium, beryllium, uranium, titanium, zirconium, thorium, cfrium, mama-

nese, magnesium, calcium, strontium, barium and moot of the cobalt,' nickel and thallium.

(3) The separation of bismuth as oxybromide from coppm, lead v cadmium, .thallium, cobalt, nickel.and (4) The determination of bismuth by the gravimetric phosphate-mannitol method or by the volumetric B.D.T.A. method. The only elements known to interfere with tie above scheme of analysis are indium and tellurium. Indium is partially precipitated by zinc powder • •

and will precipitate as hydroxide when the oxybromide separation is made« Indium interferes with both the methods of determining bismuth. Tellurium affects the separation of bismuth from some other elements as is described on page 160. When tellurium is precipitated with the bismuth oxybromide, it interferes with the determination of bismuth. Separation of Indium.

The method of separation that seemed most likely to fit into the general

scheme of analysis was the solvent extraction .of indium as the complex bromide into diethyl ether. The follartring method is based an the data given by Bock, Kusche & Bock(136) on the extraction of metal bromides into diethyl ether. Into a 100-ml. beaker were weighed 25t 1g. of bismuth and 250rng. of

dium. The metals were dissolved in a mixture of 10,11. of hydrobrcrtic' acid and 2n1. of bromine. When dissolution was complete, the solution was warmed

to expel most of the free bromine and transferred to a 100.,m1., pear-shaped separating tunnel. The beaker was washed with a mixture of 1011. of water

and 9n1. of hydrobmnic acid and the washinge transferred to the ihnnel. The hedrobronic aciA 1.13c0 was 9.02 normal. To the solution containing the biseuth and Indian were adder! 5011. or ether and the funnel was etoppered end shaken for one minute. The layers were alloeed to separate and the aqueoue layer wan run into rs second funnel containing 25ml. of ether. The rlecond funnel was etoppe.red reel rhaken far one minute, the layers were allowed to F C. tporato end the elute:fun er woe run off. To the fir at: funnel were • added 5m1. of diluted.(1+ 1) hyc'robronic acid and the above ceparation wan repeated. The ether layers were washed with a further two 5.eal. portione of diluted (1+ 1) hydrebronic acid. The ether layers were coebined, the ether leap evaporated by placing the beaker on the water-bath end tle residue was discolved in 5n1. of diluted (1+1) nitric acid. To till:: colutien war. added lel. of 60 per cent. wfw. perchloric acid and the volution was evaporated until fumes of perchlaric acid were evolved. To the reeidue were Mead 90.. of water and the robe. tion was tested fox blerretth by the co pleat iodide method. The bismuth was less then The ca bins aqueous phases were evaporated to dryneen by placing the beaker on the water-bath and the residue was•discolved in 2011. of 3N-1W chloric acid. The solution was heated to 60°C., saturated with hydrog sulphide and allowed to cool under a pressure of hydrogen sulphide. The precipitate was filtered CM a 9-en. No./41 ilhategan filter paper and the. trate was evaporated to ft,,mess by placing the baler on the water-bath. The dr3r residue wac dissolved in lQnI. of 1rT ydrochlori.c acid containing 0.005 psr cent. of *el ain and the irentra was determined polaroeraphically, the ire:tram/it described on page 3.5e being used. The a-nount, of indium round -163 was 0.02mg. The standard was prepared by dissolving 270mg. of pure bismuth oxybromide in 2CM1. of 3N-hydrochloric acid and adding le. of a standard solution of indium. Thus, the solvent extraction of indium from 4.5N-hydrobrcmic acid separates it fran bismuth. According to Bloch et a].. (136), the other elementa that are extracted to some extent are geld, thallium, iron, tin, gallium, molybdenum, arsenic, antimony, zinc, mercury, copper and selenium. Separation of Telbarium. The method of separation that seemed the most likely to fit into the general scheme of analysis was the precipitation of tellurium as the element by means of a mixture of aqueous sulphur dioxide and hydrazine hydrochloride. The foliating method is based on the information Omen by Hillenbrand et al. (loc cit. p.337). Into a 650.1m1. Phillips beakerweremighed 750mg. of bismuth and the

The metals were dissolved in 20m1. of nitric acid and 10m1. of 60 per cent. w/w. perchloric acid were added, the beaker VW transferred to a hot-plate and the solution evaporated until fumes of perchioric acid were evolved. The solution was cooled, l0Qal, of diluted (1+3) hydrochloric acid were added and the solution was heated to the boiling point. To the solution were added 20m1. of diluted (14-3) hydrochloric acid saturated with sulphur dioxide and containing 0.5g. of hydrazine hydrochloride. The precipitate was digested at the boiling point of the solution for five minutes. The solution was cooled to room temperature, the precipitate filtered on a 9-cm. No.1l Whabman filter paper and washed with diluted (14- 5) hydrochloric acid. The filtrates were saturated with sulphur dioxide and heated to the boiling — 164 point. No tellurium was precipitated. The precipitates were dried in the oven at 1100C. and their bismuth content estimated spectrographically. The dried precipitates wt re graand in an agate mortar and 20mg. were weighed on to a Ringedorff preformed electrode No.3 made of graphite (grade nwi extra). The counter-e/ectrodeused was a ningedorff preformed electrode No.10 made .of graphite (made MI extra). The sample was arced at a constant current of 6.5amp. until it was all combusted. The source unit used was manufactured by Pilger. The spectrum was recorded on an Ilford Ordinwey plate hymens of a Hilger Large Quartz spectrograph. Puplicate arcings were made on each precipitate and standard. The standards wore prepared by grinding together pure tellurium and bianuth in an agate mortar. The biemuth line 3067 was compared byname of the Hager Judd-Lewie comparator. The follcwing results were obtained:- Weight of Concentration of Amount of Di Te taken. Bi in opt. coprecipitated. 150mg. 3upPm- 4.9m. 300mg. 30ppm. Mugs 454mg. 3OPPm• 13.5ug. Thus, the precipitation of tellurium from hydrochloric acid solutions separates it from bienuth; According to Hillebrand et al. the only other elements precipitated by this method are selenium and gold. Separation of Copper. When the determination of the biemUth is to be made by the volumetric E.P.T•A. method, the oxybromide separation is unnecessary unless large anoints of copper are present. It would be simpler to make an mmmonium hydroxide precipitation after part (1) of the general scheme of analyais(eee page 160) - 165 .p than. to carry out an oxybromide separation. For this reason* the following method was tested. Weigh into a 650-ml. illips beaker 25Ortg of Isis-lath oxide* aid all. of 60 per cent. perchloric acid* lrYnl. of hydrochloric acid and of ferric chloride solution (nee page 150 for the preparation of this solution). nibite the solution to lOara. with water and heat the solution to the boiling point. Add diluted (1+ 1) aqueous ammonia siva)* and with centinuous stirring of the solution until a white turbidity is formed. Stir the solution continuously and add the aqueous an one drop at a time until the precipitation of ferric hydroxide is ccmplete* then add a further 5na. of the aqueous arionia• Beat the solution at the boiling point for one minute and filter the precipitate on a 11-cm. No.4.1 Thatman filter paper. Wash the beaker* Irecipitate and paper twice with hot 1 per cent. ErMOr!Jilin chloride solution. To. the combined filtrate and washings were added two drops, of phenol- phthalein and diluted (1+1) hydrochloric acid until the indicator changed colour. This solution was made 0.5 normal with respect to free hydrochloric acid and then saturated with hydrogen sulphide.. By comparison with known amounts of bisluth it was shown that the bismuth in the filtrates was less than 0.1mg. When the hydroxide separation was repeated in the presence of 25Ong. of copper the filtrate was deep blue in colour. The hydroxide precipitate Was d.issolved in 25m1. of hot diluted (1+ 1) hydrochloric acid* the bismuth and the copper were precipitated by the zinc powder method (see pages 149 and 150) and the copper in the precipitate was determined by the method .given - 166

on pages 157 and 158. The amount of copper found varied between 1 and 3mg• Thus, this method will reduce the amount of copper present to an amount .that will not interZere with the EX.T.1. titration of the bismuth. Two schemes of analysis have now been developed that will. enable bismuth to be separated and then determined when it is present with aluminium, antimony, arsenic, barium, beryllium, cadmium, caesium, calcium, cerium, chromium, cobalt, copper, gallium, germanium, gold, indium, iron, lead, lithium, mag. nesium, manganese, mercury, malybaenurn, nickel, potassium, rubidium, selenium, silver, sodium, strontium, tellurium, thallium, thorium, tin$ titanium, uranium, zinc and zirconium. The application of these methods to the analysis of ores and alloys is described in the next section. - 167

SECTION (iii)

Spectrographic Analysis. Throughout this section reference is made to spectrographic results; these were all obtained by the following general method. The dry eagle was ground in an agate mortar and 20ng. were weighed on to a Fingsdorff preformed electrode No.3 made of graphite (grade RWI extra). The counter-electrode used was a Ringsdorff preformed electrode No.10 made of graphite (grade RWI extra).. The sample was completely volatilised in a P.C. arc at a constant current of 6.5amp. The constant current source unit was made by 'Alger. The spectrum was recorded on an Ilford Ordinary plate by means of a Huger Large Quartz spectrograph fitted with a one to ten step 0 filter. The wavelength range recorded on the plate was 2450-3500 A. When liquids were being examined, 0.08m1. was pipmtted on to a Ringsdorff preformed electrode No.1 previously waterproofed with a 3 per cent. solution of polystyrene in benzene and the liquid was evaporated under an infra-zed lamp. The plates obtained were compared with the standard plates by means of the Pilger Judd-Lewis comparator. The standards used were of several different types and were prepared by one of the following methods:- (a)By grinding bismuth oxide or metal powder with oxides of other elements. (b)By melting bismuth metal under glycerol and adding known amounts of other metals. (c)By chemically analysing ores, minerals and chemicals. (d)fly grinding together mixtures of chemically analysed materials.

201Lphoice ofBAsmuth‘ Allove for The weber of lowemelting bismuth alloys prepared for various industrial uses in very large, and therefore it was necessary to select a fete of these for analysis. The alloys chosen were the bismuth-lead, the bienuth-tin and the bismuth-cadmium eutectics. The reasons for choosing these alloys were=- (a)The alloys sheuld be easy to sample as no segregation in likely to occur during the cooling of a binary eutectic alloy. This is not true of more cm- plicated (b)The ampunts of lead, tin and cadmium present in binary alloys are larger then in mare complicated alloys and thus such alloys are a better test of separationmethods

(c) Lead, tin and cadmium are the elements most catonly alloyed with bismuth. (d)mot tertiary alloys contain either tin or antimony and sop after these elements have been volatilised as bromides the remaining solutions are the same as those Obtataed from the binary allays. A Lts_ The metals used to prepare these alloys were of 99.959 per cent. made and were etched in diluted (14-2) nitric acid, washed with water and dried between sheets of Kleenex tiseuess The anounts of metals required to make 100g. of the alloy were weighed to the nearest Wig. and placed ireide the balance case together with a 100-m . beaker. After equilibrating for one hour, the metals were weighed into the beaker. The beaker was removed from the balance case, 20n1. of glycerol ware added and the beaker was transferred to a sand-bath. Menthe alloy appeared to be a homogeneous liquid it wee stirred for five minutes with a glass rod — 169 — and poured into a pre-heated circular ironmoule. When the alloy was solid, it was removed from the mould, washed with water and dried between sheets of Kleenex tissues. The disc of metal was sawn across a diagonal With a hack-sag end the ti4o halves were Clamped together in a vice no that it was possible to file across both the cub faces at the sale time, The first of the filings were rejected and the sample was then collected. The prepared composition of the alloys and the spectrographic results for impurities are given below. Cerrotm. Bismuth 58.03 per cent. Tin 42.00 pear cent. Iron 3ppm. Lead 3ppm. Cerrobase. Bismuth 55.30 par cent. Lead 44,50 per cent. No impurities detected.. 6000-1. Bienuth 60.00 per cent. Cattium 40.00 per cent. Iron 3ppm. Tin fippm Lead 5Oppm. The palveis of Bismuth The methods for determining bismuth in Cerrotru, Cerrob se and 6000-1 are given below. Cerrotm. Weigh 1.5g. of the alloy into a 650-ntl. Phillips beaker, add 10m1. of a- mixture of hydrobromic acid (9 volumes) and bromine (1 volume) and warn the covered beaker to help dissolve the samples When the sale has dissolved* remove the cover and add lUnl. of 60 per cent. tibr• perchloric acid. Trans- fer the beaker to the thermostatically-controlled hot-plate and evaporate the — 170 solution with the liquid terperature inside the beaker at 125t50e, when perchioric acid fumes ere evolved, heat the beaker for a further two or three minutes. Cool the solution and add 5m1. of the hydrobronic acid-brcmine mixture and repeat the evaporation and Arsine, as before. Tie-treat the sample with a farther 5111. of the hydrobromic acid-bremine mixture. Cool the solution and add 2Ces1. of diluted (1+1) nitric acid. Cover the beaker, heat the solution to boiling over a Bunsen flame and boil to expel free bromine.

Transfer the beaker to the thermostatically-controlled hot-plate, remove the cover-glass and evaporate the solution until fines of perchloric acid are evolved. Evaporate the nitric acid condensed on the sides of the beaker by blowing a stream of hot air from a Bylock industrial air blower across the mouth of the beaker. Cool the solution, add 10C)sl. of water and transfer the solution to a 250-ml. volumetric flask with water. Make the solution up to volume with water. (a) Gravinetric Transfer a 50-ml. aliquot to a 600qa.. beaker and determine the biesuth as is described on pages 85-86. (b) Volumetric Metijod. Transfer a 50 ml. aliquot to a 650-ml. Phillips beaker and add 200s1. of water and five drops of 0.1 per cent. catechol violet solution in water, Titrate the bismuth with 14/40 E.D.T.A. solution until the indicator colour changes to pure yellows To the titrated solution add, from a micro-pipette,

0.1mli of a solution containing ]mg./ml. of bismuth in diluted (1+999) perchloric acid. If a permanent change of colour is observed the reading of the burette is taken as the titre. If no permanent change in colour is -171 observed, add a fbrther 0.1ml. of the biemuth solution. If a permanent change in colour is now observed, deduct 0.0261. from the burette reading to obtain the titre. To the first solution titrated add a few drops of &MLA. solution and retain this as a colour standard for the titration of the other solutions. To standardise the E.D.T.A. solutimnweighS7Ong. of bismuth into a 650.m1, Phillips beaker and treat the bismuth as is described for Cerrotru. An alternative method of standardising the E.D.T.A. solution is described under the analysis of Cerrobase on page 173. Results. The folloding are the results obtained for the bismuth content of the standard Cerrotru. The calculated bismuth content is 58.00 per cent. E.D.T.A. method 57.92 percent. 57.93 per cent. 57.93 per cent. These results were obtained when tNit E4D,T.A. solution was standardised as is described under the analysis of Cerrobase on, page 173. EZ.T.A. method 57.98 per cent. 57.99 Per cent. 57.99 per cent. These results were obtained when the B.P.T.A, solution was standardised as is described under the analysis of Cerrotru on pages 169-170. Phosphate method 57.95 per cent. 57.92 per cent. 57.90 per cent. The bismuth in the filtrates from the phosphate method, estimated by the coin- plat iodide method, would only add about 0.01 per cent. to the found bismuth content. Spectrographic analysis of the combined precipitates gave the following results. Tin 150ppm. Iron 3Uppm. Lead appn• Silicon 5,00ppm. The silicon may be due to contamination during the grinding of the precipitate in the agate mortar. 172 -

Cerrobase.

(a) Gravimetric lTotho4. Weigh 35Qsg. of the alloy, on a seni-micro balance, into a 600-ml. beaker* add 5m1. of diluted (1+2) nitric acid* cover the beaker and warn to dissolve the sample. 'hen dissolution is complete remove and wash the cover.glass* dilute the solution to 100m1. with water and precipitate biemuth oxybromide as is described on pages 153-154. Retain as much of the precipi. tate as is possible in the beaker. Place the original beaker under the funnel and dissolve the precipitate on the paper by dropping hot diluted (14, 1) nitric acid round the rim of the paper. Wash the paper alternatively with acid and water until the total volume in the beaker is about 50m1. After the final water-wash of the paper• wash it once with diluted (1+9) aqueous ammonia. After one or two minutes wash the paper twice with water. To the solution add 2m1. of perchioric acid and transfer the beaker to thethermostatically-controlled hot-plate and evaporate the solution until fumes of perchloric acid are evolved. Dilute the solution to 100m1. with water and reprecipitate the bismuth oxybromide. Filter on the same paper* again retain as much of the precipitate'as is possible in the beaker. - Div.- solve the precipitate as before* but wash the paper more thoroughly and omit' the wash with diluted aqueous ammonia. Evaporate the solution until fumes of perchloric acid are evolved and evaporate the nitric acid that has condensed on the sides of the beaker by blowing a stream of hot air from a Bylock industrial air blower across the mouth of the beaker. Dilute the solution with water and determine the binmuth as phosphate by the method that is described on pages 85-86. - 173 -

(b) Volumetric Method,, Weigh 300mg. of the alloy, on a semi-micro balance, into a 650-ml.

Phillips beaker, add 561. of diluted (1+2) nitric acid, cover the beaker and warm to dissolve the sample. When dissolution is complete, remove and wash the covet...class and add 1.5m1. of 60 per cent. w/w. perchloric acid. Transfer the beaker to the thermostatically.-controlled hot-plate and evaporate the solution until fumes of perchloric acid are evolved. Evaporate the nitric acid that has condensed on the sides of the beaker by blowing a stream of hot air from a Bylock industrial air blower across the mouth of the beaker.

Cool the solution and dilute it with 250m1. of water, add five drops of

0.1 per cent. catechol violet solution in water and Citrate the bismuth as is described under the analysis of Cerrotru on pages 170 and 171 The E.D.T.A. solution is standardised by treating 17Umg. of bismuth by the method described for the alloy. Pesults. The following are the results obtained for the bismuth content of the

standard Cerrobase. The calculated bismuth content is 55.50 per cent. E.D.T.A. method 55.46 per cent. 55.48 per cent. 55.49 per cent. These results were calculated from a bismuth factor of 5.184 mg./61. at 20°C.,

this was the mean of the following four results 5.182, 5.183, 5.185 and 5.185 mg./ml. at 20°C. Phosphate method 55.40 per cent. 55.44 per cent. 55.38 per cent. The awn of the bismuth in the filtrates from the oxybromide precipitations and the phosphate precipitation, estimated by the complex iodide method, would add about 0.03 per cent, to the found bis'iuth content. 174

Spectrographic analysis of the combined precipitates gave the following

result. Lead 350pian. 6000-1.

(a) Gravimetric Methoct. The method of analysis is the same as is described for Cerrobase on. page :172 except that only one precipitation, of bismuth metbranide need be made. (b) Ve}trietrie Metbod. The method of analysis is the cane as is described for Cerrobase on page

173. Rasul se The following are the results obtained for the bismuth content of the standard 69004 alloy. The calculated bismuth content is 60.00 per cent.

E.D.T.A. method 59.99 per cent. 59.97 per cent. 60.00 per cent. Phosphate method 59.91 per cent. 59.95 per cent. 59.87 per cent. The sum of the bismuth in the filtrate fran the ovbranide precipitation aryl the phosphate precipitation, estimated by the complex iodide method, would

add about 0.02 per cent. to the found bismuth content. Spectrographic analysis of the canbined precipitates gave the following results. Iron lOppm. Lead 15ppn. Tin 15ppm. Cadmium less than lOppn.

The Choice or aismuth Ore for Analysis. Eight bismuth ores from different deposits situated in different parts

of the world were examined spectrographically. In the table below are given the percentages of bismuth and after this three groups of elenents, the ele-

ments in the first group are present as major constituents, the elements in 175 the secon,7 group are present in the concentration range 0.1 to 1 per cent. and the elements in the third group are present in the concentration range

0.001,to 0.1 per cent.

Ore 1 44 ('Hi Fe Si: As) (Sb Mn B) Mo Al Mg Pb) Ore 2 40 (31 Fe Al Si) ( ) (Pb)

Ore 3 46 (Di Fe Si) (Sb) (Cu' Al Pb)

Ore 4 75 (Bi Fb Fe) (V) ( ) Ore 5 44 (Di Fe Al Cu 11 As Sb Si Mg 13) Pb Mo) (Hi Ag Au pia Mn)

Ore 6 66 (81 Fe Si)• (Ti Al) (Cu) Ore 7 79 (131 Fe Si) ( ) (Sn Pb Al Mo Cu Mn)

Ore 8.,15 (83 Pe 8) (Sb As Si) (Al Cu Sn Pb) An empty bracket means that no elements were found in that concientrat ic range. 'Ore 5 which is of Bolivian origin,was chosen for analysis as it. was the most Complicated ore. examined. The Preparation of 0,re 5 for Analysis. The 'sample used was ground in an agate mortar to pass a 100-mesh sieve and air-dried. When a sample was weighed for the determination of bismuth, another sample was also weighed for the deternination of the moisture content. The moisture content is defined by the loss in weight when the sample is heat.- ed at 1100C. until constant in weight. The moisture content found was 1.35±0:05 per cent. All results are .reoorted on the sample 'tried at 110°C.

The Analysis of Bismuth, Ors 5. Weigh 1.5g. of the ore into a 650-ml. Phillips beaker and arid 1Ctra. of a mixture of hydrobrmic acid (9 vobxnes) and bromine (1 volume). After rr

alluding the mixture to stand for a few minutes, add 10m1. of 60 per cent. w/w. perchioric acid and 211. of diluted (1+ 9) phosphoric acid. Transfer the beaker to the thermostatically-controlled hot-plate and evaporate the solution with the liquid temperature inside the beaker at 125t5°C. When per-. chloric acid fumes are evolved heat the beaker for a further two or three minutes. Cool the solution and and lOnl. of the hydrobranic acid-brcraine mixture and repeat the evaporation and fuming as before. He-treat the sample with a further iomi• of the hydrobranic acid-bromine mixture. Cool the solution and add 2(. n3.. of diluted (1+1) nitric acid. Cover the beaker, heat the solution to boiling over a Bunsen flame are boil to expel free bromine. Transfer the beaker to the thermostatically-controlled hot-plate, remove the cover-glass and evaporate the solution until fumes of perchloric acid are evolved. Disparate the nitric acid condensed on the sides of the beaker by b3.awing a strean of hot air from a Bylock industrial air blower across the mouth of the becker(a). To the cooled solution add 10tha. of diluted (1+3) hydrochloric acid, heat to the boiling point and add slatily 20m1. of diluted (1+3) hydrochloric acid containing 0.5g. of hydrazine hydrochloride and saturated with sulphur dioxide. Heat the solution at the boiling point for five minutes, cool to room temperature and filter through a 9.-an. No.31 Whatman filter paper(b).

Wash the beaker, paper and precipitate with diluted (1+ 5) IlYft'ochloric acid. Collect the filtrate and washings in a 250-ml. volumetric flask and dilute the solution to volume with the diluted (1+ 5) hydrochloric acid.

(a) Grailmetric Transfer a 50-m1. aliquot to a 600.en1. beaker and heat the solution to the -177— boiling point and boil to expel most of the sulphur. dioxide. Cool the solution to about 60°C. and then add liquid bromine, drop by drop, until an excess is present. Heat the solution to the boiling point and boil to expel the excess of bromine. To the solution add lml. of a solution containing 2(3ng. of iron (moisten 10g. of ferric chloride hexahydrate with 2i1s of hydrochloric acid, add water to dissolve the solid and dilute the solution to 100111, with water)(c). Weigh 3g. of AnalaR zinc powder on to a watch.. glass. Heat the solution to boiling and add solid ascorbic acid in small quantities at a , time until the yellow colour of the ferric chloride complex is bleached. Then add the zinc powder in small portions at a time to the covered beaker, but retain about 0.1g. of the zinc polder on the watch-glass.

Remove and wash the cover, wash down the sides of the beaker with a small volume of water and heat, the solution at the boiling point until hydrogen evolution ceases. Add 150m1. of water and heat the solution to boiling. Add the remainder of the zinc polder/r and about 0.2g. of ascorbic acid. Cool the beaker in cold rurmairkg water. If hydrogen evolution ceases during the cooling, add another few milligrams of zinc powder(d). lihen the solution is cold, filter it through a 9-cm. No./41 Whabian filter paper that has been dustexi with about 5Ong. of zinc powder. Wash the precipitate, beaker and paper with cold water and retain as much of the precipitate as is possible in the beaker. Place the original beaker under the, funnel and dissolve the precipitate on the paper by dropping hot diluted

(14-1) nitric acid round the rim of the paper. Wash the paper alternatively with acid and water until the total volume of liquid in the beaker is about

100n1. Place the covered beaker on the thermostatically-controlled hot-plate 1 8 -

and heat the beaker until all the metallic particles have dissolved. Remove the cover and evaporate the solution to a email voltrne (1 to 5m1.). Add 10On'. of water and heat the solution to the boiling point and add, drop by drop, with continuous stirring of the solution, 10131. of potassium bromide solution. Dilute the solution with 200l. of hot water containing 1g. of potassium brirdele. Heat the solution to the boiling; point, add 6 to 10 drops of the mixed indicator solution and arrnonion acetate solution until the colour of the indicator is greet to greenish rev. Pigest the precipitate, at the boiling point of the solution for 15 minutes. Filter the hot solution through a 9-cm. No.h2 hbatman filter paper. Wash the precipitate, beaker aM paper with hot water and retain as much of the precipitate as is possible in the beaker(e). Place the original beaker under the funnel and dissolve the precipitate on the paper b r dropping hot diluted (1+ 1) nitric acid round the rim of the paper. Wash the paper alternatively with acid and water until the total volume in the beaker is about 100a. Transfer the beaker to the thermw statically-controlled hot-plate, add anl of 60 per cent. w/w. perchloric acid and evaporate the solution until iluites of perchioric acid are evolved. Eva- porate the nitric acid that has condensed on the sides of the beaker by blow ins; a stream of hot air from a Bylock industrial air blower across the mouth of the beaker. Cool the solution, add 6011. of water and lg. of mannitol dissolved in 10111« of water. Neutralise the solution by the drop:13e addition of diluted (1+ 1) aqueous ammonia until the first permanent precipitate is formed. Clear the solution by the addition of 10n1. of 10N-nitric acid and adjust the volume to lothl. with water. Neat the solution to about 700C. -179

Start stirring the solution and then add very slowly, drop by drop, from a burette 5m1 of ammonium phosphate solution (for the preparation of the reagents see page 84). Continue stirring the solution and add a further 25111. of the precipitant; the rate of addition of this 25s1. can be greater than for the first 5111. Heat the solution to boiling and stir continuously to cryctallise the precipitate and prevent 'Wiping. Dilute the stirred solution gradually with 306211. of hot water and again heat to boiling. Set the beaker aside on the hot-plate for 1 hour. The solution should be stirred occasionally and the temperature kept near the boiling point during the digestion of the precipitate. filter the precipitate on a poroue-based porcelain crucible and wash with hot diluted (1+ 999) nitric acid, Pry the precipitate and crucible in the oven at 110°C. and ignite at 700°C. Weigh as (b) Volumetric Method. Transfer a 50-ml. aliquot to a 60 1. beaker and heat the solution to the boiling point and boil to expellmoet of the sulphur dioxide. Cool the solution to about 60°C. and then add liquid bromine, drop by drop, until an excess is present. Heat the solution to the boiling point and boil to expel the excess of bromine. To the solution add 1ml. of a solution containing 2Ong. of iron (moisten 10g. of ferric chloride hemahydrate with 2m1. of hydrochloric acid, add water to dissolve the solid and dilute the solution to 100m1. with water)(0. Dilute the solution to 100m1. with water and heat the solution to the boiling point. Add diluted (1+ 1) aqueous ammonia slowly and with ccutinuoue stirring of the solution until a white turbidity is toned. Stir the solution continuously and add the aqueous ammonia one drop at a time until the precipitation of ferric hydroxide in complete, then add a further - 180

9/,11. of the aqueous amnenie(g). Heat the solution at the boiling point for one minute and filter the precipitate on a 11-cm. No.41 It'hatman filter paper. Wash the beaker, precipitate end paper twice with hot 1 per cent. ammonium chloride solution. Place the original beaker under the funnel and dissolve the precipitate by alternate trcabnente with hot diluted (1+ 1) hydrochloric acid and water. The volume of diluted. hydrochloric acid used should be 25m1. end the volume of water. not more than 50m1. Peat the solution and ensure that all the hydroxides dissolve. Weigh 3g. of AnalaR zinc powder on to a watch-glass. Heat the solution to boiling and add solid ascorbic acid in•smaLl quantities at a time until the yellem colour of the ferric: chloride complex is bleached. Then add the zinc powder in small portions at a time to t1-,e covered beaker, but retain about 0.1g. of the zinc powder on the watch-glans. Remove and wash, the cover, wash down the side© of the beaker with a ertall volume of water and heat the solution at the boi3.ing-point until hydrogen evolution ceases. Add 150131. of water and heat the solution to boiling. Add the renainder of the zinc powder and about 0.2g. of ascorbic acid. Cool the beaker in cold running water. If hydrogen evolution ceases during the cooling, add another few mill i 17mM of zinc pomier(d). then the solution is cold, filter it through a 9-cm. No./11 Whatman filter- paper that has been, dusted with about 911g. of zinc. powder. Wash the precipitate, beaker and paper with cold water and retain as much of the precipitate as is possible in the beaker. Place the original beaker under the funnel and dissolve the precipitate on the paper by dropping hot diluted (1+ 1) nitric acid round the rim of the paper. wash the paper alternatively with diluted (1+1) nitric acid and

water. To the solution add 1.511. of 60 per cent. w/w. perchlorie acid. Transfer the beaker to the than ostatically-controlled hot-plate and evaporate the solution until fumes of perchioric acid arc evolved. Evaporate the nitric acid .condensed on the sides of the beaker by bide/0ring a stream of hot air fran a Bylock industrial air blower across the mouth of the beaker. Cool the solution and add 250m1. of water and five drops of 0.1 per cent. catechol violet solution in water. Titrate the bismuth with 11/40 solution as is described on pages 170 and 171.

(a) This step serves to attack the sample and volatilise the volatilis bromides of selenium, germanium, arsenic, tin, antimony and mercury.

(b) The mixture of hydrazine ectd sulphur dioxide precipitates tellurian and gold.

(d) In ore analysis thin step is necessary mainly to separate iron and aluminium; a list of elements separated by this method is given on page 150.

(e) In are analysis this step is necessary mainly to separate lead; a list of elements separated by this method is given on page 160. For the prepare- tion of the reagents see page 153.

(f) The iron is necessary when the zinc polder precipitation is made (see page 147) but it is added at this point as the ferric hydroxide acts as a physical carrier for the bismuth precipitate and makes it easier to filter .

(g) The hydroxide precipitation separates bismuth from most of the copper. Results. The following. results were obtained for the bismuth content of Ore 5. E.T).T.A. method 14.71 per cent. 44072 per cent. 44.67, per cent. 44.70 per cent. 44.71 per cent. 44.68 per cent. Phosphate method 44.80 per cent. 44.75 per cent. 44.82 per cent. 44.84 per cent. Spectrographic analysis of the bismuth phosphate precipitates gave the following results:- Si 0.1 per cent. Sb 500ppn. Ag 200ppm.. .Pb 200ppm. Fe 40ppm. Sn 15ppm. Cu, 5ppm. Thuss.up to 0.3 per cent. of the precipitate weighed may not be bismuth phosphate* Normally the results obtained by the phosphate method are slightly lower than those. obtained by the E.D.T.A. method The cause of the higher results obtained by the gravimetric method for this ore is probably the impurities that were weighed with the bismuth phosphate. • Diecpssiop of .the Methgds Pevolooed. In the initial attack of the sample no provision has been made for are' bismuth not dissolved by an acid attack. In practice, however, an ore has never been analysed by the candidate that contained more than a fmw:parts per million of bismuth'in the acid-insoluble residue. The residue from Ore 5 contained less than 5ppm. of bismuth. In the event of an ore being analysed with any acid insoluble biemuth present, the residue could be treated with hydrofluoric acid to volatilise silicon tetrafluoride, the rtsidue.fUsed with sodium carbonate, the leached melt acidified with hydrochloric acid and the solution combined with the main solution. 183

. puring the volatilisation of the volatile bromides of selenium, german-

ium, arsenic, tin, antimony and mercury, some bismuth is also volatilised. This loss, and the factors that affect. the extent of the loss, have already been discussed on pages 129-139. One interesting fact emerges from the study of thin loss, and this is that the amount of bismuth volatilised in not proportional to the amount of bismuth present. As the total amount of bis-

muth gets smaller, the percentage loss gets larger down to about Stang. of bismuth when the less is 1 per cent. of the total bismuth present. In sone work done by the candidate (not reported in this thesis) the loss is still about 1 per cent. when the total bismuth in only 1mg. With these smaller amounts of bismuth, no precipitation of bismuth bromide occurs at the end of the evaporation and therefore, all the bismuth is in solution. Once the amount of bismuth present is increased sufficiently to cause a precipitate to form, the amount of bismuth in solution is constant however much more bismuth is present. Thus, if the volatilisation of bismuth takes place predaninantly

from the solution, the amount of bismuth volatilised would not, increase lin- early with the amount of bismuth present. . Although the zinc powder precipitation gives a good separation of his . muth from a large number of elements (see page 150), some of the separations may fail if certain ombinations of elements are present. This is because the addition of the zinc powder is, in effect, a neutralisation of most of the free acid, Thus, if titanium or zirconium was present and phosphoric

acid had been added to form a canplex with iron, titanium or zirconium phosphate might be precipitated. Ore 5 contains titanium, but spectrographic results show that nearly all the titanium remains unattacked„ and although a mall amount of titanium was detectable in the hydroxide precipitate, none. was detectable in the zinc-poader 'precipitate. Apart from the quantitative work reported on page 182, separate.aliquote of the prepared solutions from Ore 5 were taken through the !methods described on pages 175-181 and all the solutions and precipitates Obtained were examined spectrOgraphieolly. All the elemente present behaved as was expected from the work carried 'out with synthetic solutions. Tungsten was'the only element present that had not been studied and most of this element was separated with the acid-insoluble residue from the ore. In the volumetric method, the

small amount eftungsten that passed into solution. Was precipitated with the hydroxide precipitate but only about 50pg. were precipitated with the sine- polder precipitate. In the gravimetric method, the small Mount of tungsten

that- paused into solution was mostly separated by the zinc-powder precipitation. The mall mount of tungsten remaining with the bismuth was precipitated by the oxybrmide method but remained in the filtrate fran the phos-

phate precipitation. It lathe candidate's opinion that the E.D.T.A. method in the superior of the two methods for the following roe:sone.

(1) The time required for anaiyaie is much less. A complete ore analysis, can be performed in duplicate by the E.D.T.A. method in a working day. The gravimetric method requires at least two working days for completion.

(2) When analysing complaxmaterials# such as Ore 5, it is impossible to obtain very pure bismuth phosphate for weighing and for this reason the results obtained with the E.t.T.A. method are likely to be more accurate.

(3) When analysing bismuth alloys by the E.D.T.A. method, no separations are neceseary unless indium is present. This is not true of the phosphate method . (4) ath the E.D.TA. method the whole analysis can often be perforsed in one beaker without hilly any manipulation and therefore, high precision is easily obtained. Because of the method of standardisation this means that high accuracv is also obtained. In conclusion, it may be stated that both methods are capable of giving good reedits, but in most instances the results can be obtained more easily by the EX.T.A.method. ,Appendix •I

In this Appendix is mentioned some work that was started but not

continued for the various reasons given.

(1) The separation of bimuth from copper, lead and Cadmium was examined by the owchloridemethod described on pages 63-64. The separations obtained by this method ware about the sane as those obtained with the ow- brcmide method. The method was not pursued for the reasons given on page 66. (2) The removal of chloride from bismuth oxychloride was attempted by evaporating a solution of the precipitate in a mixture of nitric and per. chlorie acids to fumes of perchioric acid. Even after four evaporations, 15 per cent. of the original chloride was not volatilised. When bismuth oxybraside was treated in the someway the bromide was reduced to Oamg. after one evaporation. This was another reason for preferring the oxYbromide to the owchlaride. (3) The precipitation of bismuth as oxalate, as reported by Mhir(178), was examined as it seemed poesible that this method might provide a separation of bismuth from tin and antimony. However, it proved impossible to reduce the amount of bismuth passing into the filtrate to less than 0.5mg. 'In the presence of ammonium salts, the amount of bismuth in filtrates increased to 1 to 21g. The amount of bismuth in the filtrates was also very dependent on the oxalate concentration.

(4) The solvent extraction of quinquevalent antimony as the complex chloraeid from 9N-hydrochloric acid into iso-propyl ether was studied(340). The method 187 worked well* but the separation of antimony was carried out more easily by the volatiliration of antimony branide. Appendix It

The weights used were rhodium-plated brew and were calibrated by the method of Richarda(341). The weights were calibrated in (1) October 1954, (2) June 1955, (3) October 1955, (4) June 1956, (5) Januar', 195? and (6) June 1957. Calibrations (1), (2), (3) and (5) were made on an Oertling RelesoRatic balance and calibration (4) and (6) were made on an Oertling serni-micro balance. Noninal Value Corrections in mg. of Weight in g. (1) (2) (3) (4) (5) (6) 0.0]. +0.1 +0.1 +0.1 +0.15 +0.1 +0.10 0.01 0.0 0.0 +0.1 +0.05 0.0 +0.05 0.02 0.0 0.0 0.0 0.00 0.0 0.00 0.05 -0.1 -0.1 -0.2 -0.15 -0.1 -0.15 0.10 0.0 0.0 0.0 0.00 0.0 0.00 0.10 +0.2 +0.2 +0.1 +0.15 +0.2 +0.15 0.20 0.0 0.0 0.0 0.00 0.0 0.00 0.50 0.0 0.0 0.0 0.00 0.0 0.00 1.00 -0.1 -0.3. 0.0 -0.05 -0.1 - 0.05 1.00 -0.1 -0.1 -0.2. -0.15 -0.1 -0.10 2.00 + 0.1 +0.1 +0.1 +0.10 +0.1 +0.05 5.00 0.0 0.0 0.0 0.00 0.0 0.00 10.00 - 0.2 -0.2 -0.3. - 0.15 -0.2 -0.15 10.00 +0.1 +0.1 0.0 + 0.05 +0.1 +0.10

- 189..

Corrections in calibrations (1), (2), (3) and (5) are given to the nearest 0.1mg. Corrections in calibrations (4) ,and (6) are given to the nearest 0.05ng. Volumetric Amaratuti. The methods used to calibrate volumetric glassware were those deedribed by- Kolthuff &:stenger(342). The following results were obtained:. Flasks.', Nominal Volume. Cnlibrated volume. 250n1. 250.02±0.01ral. Three calibrations. 1000n1. 999.9M.02m1 Three calibrations. Fjrattitsg• Nominal. volume. Calibrated volume. 541. 5.025±0.002 Six calibrations. 10n1. 10430±0.005 Six calibrations. 25n21. 25.02t0.005 Thirty'Three calibrations. 5031. 50.00±0.01 Six calibrations. Burette. Nominal volume Calibrated voila.. 5n1. 5. 1. Two calibrations. 1041. 10.00 nl. 1%1. 15.00m1. 20n1. 19.99811. 2941. 24.9an1. 29.9941. 39n1 35.00m1. n ft 40s1. 40.00121. Oa. 45.00ml. Two calibrations. 50u1. 50.00m1. Porous-Dase4 Berlin Porcelain Crucibles. •Bel0W is given the weight history of two of theme crucibles. For the methods of cleaning then see page 56. The first weight is the weight of the new crucible after cleaning and igniting, and each aubeequent weight is the weight after the crucible has bemused once, cleaned and then ignited.

Weight of Weight of . Crucible A Crucible B in g. in g. 18.2191 174780 18.2192 17.9779 1B.2193 17.9779 18.2193 17.9778 18.2192 17.9777 18.2191 17.9784 18.2191 17.9782 18.2186 17.9784 18.2186 17.9784 18.2186 17.9783 16.2170 1.9769 Cleaned in nitric-chronic acid overnight. 18.2170 44770 18.2169 1.9770 18.2169 4.9769 18.2169 1t.9769 16.2166 *9768 10%9768 4.09769 18.2168 x'•9768 18.2167 X•9769 18.2161 *9762 Cleaned in nitric-chronic acid overnight. This sort of sequence of weights was continued over a total of 152 weighings for crucible A and 163 weighings for crucible B. The weights of the crucibles when last used were 18.2150g. for crucible A and 10.9742g. for crucible B. The period over which the crucibles were used was approximately 2 years, -192—

(1)Chancel, Copt. Rend. 120 417, (1860). (2)H. Salkoweki, album, fur Prakt. Chem. CO: Ulu 172, (1868). (3)A. Staehler & Scharfenberg, Der. xi 3862-3869, (1905). (4)R. Salkowski, Ber. 8, 3943-3944, (1905). (5)L. Moser, Zeit. Anal. Chen.. A10 19-26, (1906). (6)A. Staehler, Chem. Zeit.:,}, 615-616,11907). (7)A.P. Castanares, Eighth Inter. Cong. Appl. Chem. g2, 39-40, (1912). (8)H.F.V. Little & E. Cahen, Analyst* :10 301.306, (1910). (9)J.G. Galletly & G.G. Henderson, Analyst. 2i0 389-391, (1909). (10)W.R. Schoeller & E.P. Waterhouse, Analyst. AZ 435-439, (1920). (11)G. Luff, Chem. Zeit. tar, 133-134, (1923). (12)G. Luff, Chem. Zeit. Ag6 61, (1924). (13)P.P. Solodovnikov, Uchenuie Zapieki. Kazan. Gosudarst. Univ. „2,8 873-875, (1929). (14)W.C. Blasdale & Perle, Ind. Eng. Chem. Anal. Ed. 8 352...35 1936). (15)W.R. Schoeller & D.A. Ladbie, Analyst. 100 533-537, (1937) (16)R. Belcher, A.J. Mitten, E. Parry.&11.I. Stephen, Analyst. 810 4, (1956). (17)L. Silverman & I. Shideler, Anal. Chem. gg, (5), 911-914, (1954). (18)G. Vortmann, Bar. au 2749-2765, (1891). (19)D. Ealachweld,Compt. Rend. 1320 179-182, (1900). (20)K. Wimmeneuer, Zeit. Anorg. Chen. a2, 1.24 (1901). (21)0. Brunk, Ber. :10 1871.1873, (1902). (22)A, Bollard & L. Sertiaux, Compt. Rend. 1:20 366-367, (1904). (23)F.J. Metzger & R.T. Beans, Journ. Amer. Chen. Soo. 3z 589-593, (1908). (24) J. Paset, Zeit. Anal. Chem. h2, 401, (1908). (25) E.P, Schoch & D.J. *min, Eighth Inter. Cong. Appl. Chen. 81-91, (1912). (26) 8.13, Richardson, Zeit. Anorg; Chem. fio 277-.317. (1913). (27) P. Poch, Anal, Fie,0Ailm. 1A, 520-533. (1918).' (28) A.J. Engelenberg, Zeit. Anal. Chen* kap 257-284, '(1923). (29) A. Lassieur,' Comptes Rend, ja, 632634,' (1924). (30) A. Lassieur, Comptes Rend. 121, 847849, (1924)., (31) K.Seal, Zeit. AngeN. Chem.' 541-543, (1924). (32) A, Jilek & J. Lukas, Chen. Liaty.ala 49-55, (1927). (33) A. Jilek & J. Lukas, Coll. Czech. Chem. Comm. 11 369-376, (1929). (34) Eji* Collin, Analyst. a, 654-657, (1929). (35) H. Sand, J. Chem. Sac., S1, 385, (1907). (36) I.D. Chetverikov, J. Inst. Metals* k2A 438, (1930). (37) Kny.Jones, Analyst. go 172-175, (1939). (38) Analyst. (14.8. 575-574 (1939). (39) F.G. K1.7-Jones, Analyst. 46, 101-10k, (1941). (40) L Vanino & F. Tre0erb, Beri mo 1303, (1898)• (41) S.B. Tallantyre Amer, Journ. ?harm. 22, 344, (1921). (42) A. Kurtenacker &Fa Werner, Zeit. Anorg. Alige. Chen. lay 166470, (1922). (43) 144 Muthmann-& F. Mawraw, Zeit, Anorg. Chem. 13, 209-210, (1897). (44) E. Rupp & G. Hamann,. Zeit. Anal. Chem. g2, 32-35, (1932). (45) R. Cousin, Journ. Pharm. Chim.gg, 179-184 (1923). (46) L. poser & A. Brukl, Monate, AL 722,'(1926). (47) L. Moser, Die Bestimmungenethoden des ilientit and seine l'renrung von den anderen Elementen. Stuttgart (1909). -194-

(48)W.F. Millebrand. G.E.F. Lundell, B.A. aright & J.J. Hoffman, Applied Inorganic Analysis, New York and London* (1953). (49)K. Seubert & 1. Eaten, Zeit. Anal, Chem. j, 76, (1893). (50)F. Hecht & R. Reissner, Zeit. Anal. Chem. 14a, 186-189, (1935). (51)R. Nantes, Chem. Zentr. lao 2079-2080* (1907). (52)0.A. Critchett* Eng. Mining. Journ. Ma' 58, (1921). (53)Arppe, Pogg. Ann. §.6 249, (1845). (54)G. Luff, Zeit. Anal. Chem. fla 343, (1923). (55)W. Hiltner Gittel, Zeit. Anal. Chem. 220 170-171, (1934). (56)J. Donau, donate. 1127, (191)). (57)K. Jillenek &W. Kuhn, Zeit. Physik. Chen. 125, 337-355, (1923). (58)I.Sarudi, Zeit. Anal. Chem. la50 108-110* (1943). (59)J. Antal, Mineral. Abs. 10 480, (1928). (60)DX. Jessup, Eng. & Min. Journ. 603-604, (1918). (61)G. Lunge & C.A. Keane, Technical Methods of Ore Analysis, Vol II. (62)A.I. Vogel, Quantitative Inorganic Analysis, London (1951). (63)F.P. Treadwell & W.T. Hall, Analytical Chemistry* Vol II Quantitative Analysis. Ninth Edition. J. Wiley : Chapman & Hall, (1942). (64)W.W. Scott & N.H. Furman* Standard Methods of Chemical Analysis. Vol I The Elements... .Fifth Edition. Van Nostram: Technical Press (1939) (65)W. Fresenius 8fG4 Jander„ Third Part. Vol V42. Arson, Antimon and Wismut. (1951). (66)R. Strebinger & W. Zins, Mikrochem.1, 166-192, (1927). (67)R. Strebinger & W. Zins, Zeit. Anal. Chem. 7& 417-429; (1927). (68)R. Strebingeric11. Ortner, Zeit. Anal. Chem.fl 14 14-17, (1936). (69)F. Hecht &R. Reicsner* M3krochem. la, 283-288, (1935). (70)Y. Kakita, Journ. Cher,. Soc. Japan. 435-439, (1944). -195-

(71) J. Lowe, Journ. fur. Prakt. Chem.(1) 220 344, (1858) (72) C.H. Pfaff, Handbuch von Analytischen Chant% Altona (1921). (73) O. Steen, Zeit. Angea. Chen. gi,„ 530-535, (1895). (74) G. Luff, Chem. Zeit. Akio 71, (1920). (75) G. Luff, Zeit. Anal. Chen. LIJ 330-348, (1923 (76) H. Blumenthal, Zeit. Anal. Chen. 241, 206-213, (1929). (77) H. Rose, Pogg. Ann. (2)41 190, (1841). (78) J. Lowe, Journ. fur Prekt. Chem. 22P:, 73, (1859). (79) F. Challenger & A.B. Ck*Iderd, 'loam. Chem, Soc. 773, (1920). (so) L. Moser & E. Neusser, Chen. Zeit. i2„ 542, (1923). (81) H. Flaachka & H. Jakobljevich, Anal. Chin. Acta. A, 351-355, (1950). (82) I.K. Taimni & G.B.S. Saari% Anal. Chien. Acta. 310 54-61, (1954). (83) h.!anchot, G. Grassl & A. Schneeborger, Zeit. Anal. Chen. AI, 177-195, (1925). (84) S. Ramachandra% Chen. Newas 2110 386, (1925). . (85) G.E.F. Lundell & J.I. Hoffman, Outlines of Methods of Chemical Analysis (1938). (86)W.H. Keefe & I.L Newell, Chenist-Andlyst. as 8, (1932). (87)R. Berg &M. Teitelbaum, Zeit. Anorg. Mom. Chen.lgs 101.102, (1930). (88)O. Funakoship Journ. Chem. Soc. Japan. 433434, (1932) (89)0. Funakoship Bull. Chem. Soc. Japan. 190 359-362, (1935). (90)G.S. feshmUkh & E.T. Varkey, Journ. Ind. Chem. Soc. Q, 645-646, (1953). (91)B.H. Miller & F. Van Tyke Cruser, Jaarn. Amer. Chen. Soc. g2„ 116.121, (1905). (92)C. Mahr, Zeit. Anorg. Aligen. Chen. go, 313-316, (1932). (93)C. Mehl., Zeit. Anal. Chem. 2g0. 6-9, (1940). - 196 -

(94)G. Spacu & P. Spacu, Zeit. Anal. Chem. 52, 260-265p (1933). (95)0. Spacu & G. Sucio. Zeit. Anal. Chem. 22i 196, (1930). (96)H..Hermogp Chem. News. 1g4 3.29, (le...), (97)A.L. Benkert & B.F. anith. Journ. Amer. Chen. Soc. 20.1 1055-1056. (1896). (98)F. Feigl & H. Ordeltp Zeit. Anal. Chem. fzi 448-451, (1925). (99)R. Strobinger & 3. Flaschnerp Mikrochem. 5o 12-15, (1927). (100)R. Berg, Zeit. Anal. Chen. 24, 1776419, (1927). (101)H.G. Haynes, Anayst. 129.131,1(1945). (102)F. Hecht & R, Reissnerp Zeit. Anal. Chen. 123, 261-269, (1935). (103)A. Jilek &M. Krivanekp Chen. Zvesbi. 2, 563..669, (1953). (104)A. Pinkus &J. Dernies. BUIL Sec. Chin. Beig. , 267.283, (1928). (105)B.A. Ostreemovp Zevodskayap Lab. 4, 1016-1020p (1935). Zeit. Anal. Chem. 10, 36-45, (1936). (106)P. Nath Pas-Gupta, Journ. Ind. Chen. Soc. §o 627-633, (1929). (107)L. Kieft & G.C. Chandlee, Ind. Eng. Chem. Anal. Ed. go 392, (1936). (108)B. Berg & B.S. Fahrenkanp, Zeit, Anal. Chem. 161-169, (1938). (109)A.K. Majumdar, Journ. Ind. Chem. Soc. ia, No.4, 119-124, (1944). (110)A.K. Majmndarp Journ. Inds Chen. Soc. al, 187, (1944), (1i1) A.K. Majunderp journ. Ind. Chen. Soc. gao 188-190, (1910. (112)A.K. MajmearAiR.N. Sen. Sam, Journ. Ind. Chem. Soc. go 477-482 (1949). (113)A. Musil & P.. Pietschp Zeit. Anal. Chen. lAko (5), 347350, (1955). (114)S. Takaki & Y. Takase. Journ. Pharm. Soc. Japan. go 405-408, (1936). (115)S. Takaki & Y. Nagasep Journ. Pharm. Soc. Japan. go 74-76, (1936). Chen. Zentr. lo 941, (1937). (116)H. Etienne, Bull. Soc. Chin. Beig. 287-303, (1958). _197

(117) P.P.'Solodevnik .Trana. Inst. Cheme Tech. Kazan. g6,57.600, (1940). (17.B) G*'Spadh &Me Kuras, Bull Soc.' Stiintes CIUN ft, 243-244, (1935).. Zeit. Anal. Chem. lag 68-93, (1936). (119)M.-KUras, Chef. Obzor. 9546, (1936). (120)F.Teeht. & K. eissner, Zeit. Anal, Chem.. 22,16 8e-98, (1935). (121)4.r. Flagg & 1411. Furman, Ind. Eng. Chem.,Anal. Ed. 12, 663..665, (1940). (122)R.Ehrenfeld, Zeit. Anal, Chen, 1164 710-711, (1907). (123)M.M.P Muir, Journ. Chei. Soc. 674-679, (1877). (12k) R. Ehrenfeld & A. Indra, Zeit. Anal. Chem. Ag„ 24-26, (1909). (125)F. Rerpiton, Chen. Zentr. 400 20/8, (1907). (126)L Yassallo, Gaze. Chico. Italia, 204..212, (1911). (127)L. Kurth), & N. Miler, SioeNsm. Zeit. laj 377-384, (1924). (128)C.V. Bordeianu, Ann. Set. Univ. Jassy. 160 546-550,,(1931).

(129)W. Streetcar & A. Rommnann, Zeit. Anal. Chem..220 5-11, (1927)". (130)A.F. Holleman' Recueil des Travaux Chimiques des Pays.43as.t,48 5.

(131)W. Strecker & P. Schiffer, Zeit. Anal. Chem. 416 495-499, (1911). (132)M.M.P. Muir, Journ. Chen. Soc. 220 483-488, (1876). (133)F. Mohr, Lehrbuch der chemisch-analytiechen Titriermethode, 7 M. Braunschweig, (1896). (134)E. Rupp & a. Schaumann, Zeit. Anorg. Chem. 20 362-365, (1902). (135)5. Utsumi, Journ. Chen. Soc. Japan. Pure Chem. Sect. 21 342-3479 (1952). (136)R. Bock, N. Kueche & E. Bock, Zeit. Anal. Chen, =0 167, (1953). (137)H.S. Piederer, Journ. Amer. Chen. Soc. y, 907..919, (1903). (138)E.H. x4t17Ar & 14 Frank, Journ. Amer. Chen. Soc. Z1, 919..928, (1903). - 198

(139)L..1Ueer, Zeit. Anal. Chen. g, 223-241, (1907), (140)Buisson & Ferraro Montt. Scient. (3), 2, 900, (1873). (141)E. Rupp & L. Krauss, Archiv. der Pharm.,/aa 443, 11903). (142)R. Castagnau, P. Cazaux and P. David, TULL .Soc. Pharm. Bordeaux. fu, 20-24, (1949). (143)G. Cannori & 0. Perin% Gazz. Chico. Ital.51, 1, 231-236, (1922). (144)J. Manus, Zeit. Anorg. Chem. 32, 115, (1698). (145)F. Mohr. Lehrbuch der chemisch-analytischen Titriermethode, . ' • . Braunschweig, (1886). (146)0. Ferrichs, Chen. Zentr. (1), 277,,(1901). Apoth. Zeit. 2,4, 859, (1901). (147)C. Baedeker, Leibig. Ann. 112, 198, (1861). (148)E. Waite. Zeit. Anal. Chem. ,1..1) 158, (1371). (149)J. Valentin, Zeit. Anal. Chem. 510 7689, (1915). (150)H. Rose, Handbuch der Analytischen Cherie, 5th Ed. (1851). (151)R. Freseniusv Anleitung zur quantitativen Analyse.6th Ed. 1877. (152)M. t. Krillov, J. Appl,-Chen. U.S.S.R. 51, 932-936, (1936)! (153)A. KUrtenackert Naturprodukte. 140-145, (1923). (154)A. Kurtenacker & F. Werner, Z..Aparg. AIlgeme Chem. 166-170, (1922). (155)G.G. Reiesaue, Z. Anal. Chem. 29J 300-308, (1927). (156)H. Kubina & J. Piichta, Z. Anal. Chem. 2, 201-207, (1927). (157)G.J. Hough, Chemist Analyst, 11. 3-4, (1929). (158)J. Hanus & A. Jilek, Chem. Listy. ji, 8-12, (1924). (159)J. Benue & A. Jilek, Chem. Zentr.Tom, 1460, (1926). (160)A. Lespappol Merville Crow, Campt, Rend. Soc. Biol. 530-532, (1944). (161)A. Leapagnol, R. Merville & J. Dequedt, Bull. Soc. ?ham Lille. No.1, 25-26, (1947). -199-,

(162)E. Zintl & A. Rauch, Z. Anorg. Allgem. Chan. 122, 397410, (1924). (163)E. Zintl & A. Rauch, Z. Anorg. =gem. Chen. laj 291-298, (1925). (164)E. Zintl & A. Rauch, Z. Electrochem. 428-430, (1925). (165)A. Oliverio, Ann. Chin. Applicata. igo 211-216, (1931).

(166)0. Tomicek & J. Mandelik, Chem. tasty. j, 169-176, (1949). (167)H. Brintanger & F. Radix, Z. Anorg. Chem. 4010 53-59, (1927). (168)R. Brintainger & F. Rodie, Z. Electrochem. 34, 246-250, (1928). (169)J. Volbard, Ann. Chem. Pharm. 190, 3, (1878). (170)W. Hiltner Gittel, Z. Anal. Chem. ,, 169-178, (1934). (1'71) E. Van Migray, Chen. Ztg. 12A 774, (1933). (172)J. Straub, Z. Anal. Chem. 51, 108-112, (1929). (173)M. Shchigol & Tn. Halsduas Farm. Zhur. 16 No.1 13-16, (1941). (174)C. Reichard, Pharm. Zentr, 103404, (1913). (175)L. Fauchon & L. Vignoli, J. Pharm. 337-341, (1937). (176)R. Berg & M. Teitelbaum, Chem. Ztg. 142, (1928). (177)H.T. Oucherer & F.W. Meier, Z. Anal. Chem. , 351-361, (1931). (178)M.P. Mir, Journ. Chen. Soc. 330 70-72, (1878). (179)M.P. Muir & C.E. Robba, Journ. Chem. Soc. blj 1-4, (1882). (180)A.W. Warwick & T.P. Kyle, Chem. News. fa, 3-4, (1902). (181)E. Cattelaine, J. Plum. Chien. (8), 21, 484-496, (1930). (182)R. Berg & 0. Wurm, Ber.6111, 1664-16710 (1927). (183) Kolthoff & F.S. Griffith, Incrochimica Acta. 3, 46-51, (1938). (184) J.R. Hayes & G.C. Chandlee, Ind. Eng. Chem. Anal. Ed. up 531-532, (1939). (185)R.S. Beale & G.C. Chandlee, Ind. Ear. Chem. Anal. Ed. lko 43441 (1942). -200

(166) 0. Schsarzenbach, W. Biedermann & F. Bang erter Helv. Chian.. Acta. 811-818,9 46) 4. (187)G. Schwarzedbach, Halve Chico. Acta. a, 1338, (1946). (188)R. Pribil, Z. Koudela, Sca, Matyaka, Chen. Listy. kb, 222-224, (1950). •Coll. Czech. Chen. Ctmm. t, ea, f1951). (189)0. Lanigren, Svensk. Farm. Tid. 241-245, (1952). (190)K.B. Gronkvist, Far. Revy. 2, 305-312, (1953). (191)M. Malat, V. Suk & 0. Ryba, Chem. Liety. Ag„ 203-206, (19 ). (192)J.S. Fritz, Anal. Chem. 26, 1978-1980, (1954). (193)K. Lu. Cheng, Anal. Chem. 1977497e, (1954). (194)A.L. Underwood Anal. Chem.,, 1322-1324, (1954). (195)R.N.Wilhite & A.L. Underwood, Anal. Chen. ii7J 1334-1336, (1955). (196)K. Ter Haar, & J. Hawn, Anal. Chin. Acta. 346 108-112, (1954). (197)L. Malaprade, Ann. Chlm. Anal. Mims, Appi. ag, 5-80 (1940). (198)C. Mahr, Z. Anal. Chem. 230 433437, (1933). (199)J.F. Reith &C.P. Van Dijk, Chen. Weekbaad. 3§0 343-344, (1939). (200)G.C. Stone, J. Soc. Chirt Ind. A, 416, (1887). (201)F.D. Snell & C.T. Snell Calorimetric Methods of Analysis, third edition 1949. (202) Colorimetric Determination of Traces of Metals, second edition 1950. (203)Bibliography on the determination of big-lath in food and biological materials, Analyst. 2, 607-608, (1933). (204)A.I. Buss!, Chem.' Tech. (Berlin). 5) 243-251, (1953). (205)C.J.W. Wiegand, 0.H. Lann & F.Y. Kalich, rock &g. Chan. Anal. 912-915, (1941).

(206)H.T. Rocrell, Journ. Soc. Chem. Ind. 2?, 102-101, (1908). (207)C.S. Leonard, J. Pharniacol. Exp. ?her. gg, 81-87, (1926). 201 -

(208)C.O. Jones & E,C. Frost, Id, erg. Chem. 11, 596, (1926). (209)13.5. wane, Analyst. La, 571, (1927). (210)Fiscal Policy Technical Sub-cosmittes of the Brass and Copper Industries Analyst. 475-476, (1933). (211)L.A. Haddock, Analyst, 28 163-1680 (1934). (212)W. Autenrieth & A. Toyer, Chen. Zentr. II, 220-221, (1924). (213)E,W. Colbeck, S.W. Craven & W. Murray, Analrilt.460 395-399, (1934). (214)P. Planes, J. !Urn. Chin. la, 385-389, (1903). (21.5) H. Saggesgaard.aamussen, K.A. Jackerott & S.A. Schou, Pansk. Tide. Farm. 11 391403, (1927). (216)R.C. SprouU & A.O. Gettler Ind. Eng, Chen. Anal. Ed. 246 462465, (19141). (217)L.C. Nickolls, Analyst. 52, 684, (1933 (218)H. Got* & S. Suzuki, J. Chem. Soc. Japan. Pure Chen. Soot. 210 142-145, (1953). (219)N.J. Giacamino, Ind. Eng• Chem. Anal. Ed. 12, 456-458, (1945). (220)E4'Peehard, Copt. Rend. 224 1188-1189, (1900). (221)A.- Portnoy & V. Skvorzov, Farm. Zhur. 534-539, (1928). Chem. Zentr. 14 114, (1929). (222)Koster, Chem. Zeit. A20 22, (1923). (223)T.C. Cloud, 40ern. Soc. Chem. Ind. alj 523-524, (1904). (221) H.A.B. Motherwell, Eng. Min. Journ. 1091-1092, (1917). (225)W.T. Phillips, Eng.- Min. journ.10,, 882.883, (1910., • (226)K.A. Hofmann & K.L. Gender, Bar. j2, 242245, (1904). (227)C.' Mahr, Z. Anal. Chem. 20 161-166, (1933). (228)A. Jilek, Chen. tasty. 1A0 165-166, (1920). (229)He Pohi, Angew. Chem. 4A, 608-610, (1952).' (230)W. Nielech & G. Boltz, Z. Anal. Chem. 2a, 13-17, 168-172 and 321-329, (1954). (231) ' S.L. Tompsett,' Analyst. Al 250-252, (.938). (232) F. Leutweins Z. Ver. Nut. Chem. Beih. No. j„ 110-112, (1944). (233) K. Woldemar & Groshelm-Krysko, Z. Anal. Chem. 2i20 399-402, (1941). (234) D.M. Hubbard, Ind. Eng. Chem. Anal. EA.11) 343-345, (1939). (235) H. Fischer, Angewe Chem. la, 919-932, (1937). (236) H. Fischer & G. Leopold', 2. Anal. Chem. 112, 182-184, (1940). (237) C.A..Gree•lPafs 3. Assoc. Official. Agr. Chem. iho Al, (1941). (238) D.M. Hubbard, Anal. Chem6 241, 363-364, (1948). (239) H.P. Laug, Anal. Chen. a) 188-189, (1949). ° (240) 143. Reynolds,'Tithizone's Reagent'for mercurri nines cadmium and bismuth. Hopkins and Williams Ltd. Reagent Monograph No.32 (1957). (241)L. Cunt' and G. Poirot, J. Pharm. Chlm: gg, 215-223, (1923)6 (242) . C.E. Laporte, J. Pharm. Chien. gat 304.305, (1923): (243)M. Pico% Bill. Soc. Chtn. (5), 10 926-934, (1934). (244)A. Okac, Chem. Linty. so 27-30, (1938). (245) T.S. Burkhalter & J.F. Solarek Anal. Chem. az 2125.1126, (1953). (246) A. Girard & E. Fourneaus 'Compt. Rend. aglo 610-611,11925). (247) C.A. Hill Lancet. as 1281, (1925). (248) B. Sazerac & J. Pouzerguess'Compt. Rend. Soc. Biol. =a 79.42, (1932). (249) F. Melengreau & G. Delrue,' Arch. Intern. Med. Exptl. 20 35-46, (1925). (250) L.' Kurthy & H. Muller, Biochem. Zeit. wo 235-23e; (1924). (251). T., umamotos, Bull. Inst. Phys.' Chem. Res. (Tokyo). 12, 1265-1266, (1934), (252)T. Yamamoto, Ball. Inst. Phys. Chen. Res. (Tokyo). go 1312-1317, (1937), (253)M.I. Tarasenko & V.I. Petrashen, Investiya Hovocherkassk. Ind. Inst. ks (20), 69-74, (1940). (254) L. Melons', Rend. Accad. Sci. NOP01 gs 8340, (1932). - 203

(255)I.A. Stolyarova, Zhur. Anal. Khim.g6 270.278, (1953). (256)C. Merritt Jr.,.H.M. Hershenspn & L.B. Rogers, Anal. Chem. 21, 572-577, (1953). (257)H. Heinrichs & M. Hertrich, Glastech, Ber. 112-115, (1924). (258)J. Kinnumen & 3. Wennerstrand, Chemist Analyst. III 88-89, (1954). (259)R. Bode, Z. Anal. Chem,1a, 182-194, (1954). (260)T.W. Nest &H. Coll, Anal. CheM. gara 1221-1224, (1955).- (261)A.K. Majumdar, Science and L'ulture. 2, 458-459, 11942). (262)A.K. Majumdar, J, Ind. Chen: Soc. al, 240.244, (1944). (263)J. Gupta &B. Chskrabartiy, J. Sci. Ind. Res. (India). a No.8, 133-137, (1949). (264)A.K. Majundar, J. Ind. Chem. n4 347-351, (1944), (265)if. Teitelbaum, Z. Anal. Chen. ga, 66-374i'(1930).

(266)C.E. agett, J. Ind. 130g. Chen.., 28, (1910).

(267) So Kallmann, Anal. Chem. al 3.291.-693, (1951). (263) E.A. Ostrommov, Zavodskaya tab. DJ 1226.1229, (1939). (269)S. Kallmann, Ind. Eng. ahem. Anal. Ed. DJ 897-900, (1941). (270)L. Mbser Maxymowics, Zeit. Anal. Chem. §2, 248-256, (1925). (271)C. Frick & H. Encenann, Chem. Zeit. 52, 601.602, (1929). (272)J. Clarke, J. Soc. Chen. Ind. 146 26-27,11900). (273)H. Funk & J. 1.4Anzierl, Z. Anal. Chem. ga, 380435, (274)D.W. Jessup, Eng. eiTta. Journ.gb 603-604, (1918). (275)E.W. Todd, Univ. Toronto Studies Geol. Sei. Ho.12, 16-19, (1921). (276)A.T.Etheridge, Analyst. 25, 279, (1950). (277)V. Hassreidter Zeit. Anal. Chem. ks 128-134, (1924). (278)R. Pribil & J. Cute, Coll. Czech, Chem. Commun. lkj 3917397, (1951). (279)11. Bode, Zeit. Anal. Chem. Wu 165-186, (1955). (280)T.S. West, Metallurgist A24 41-46, (1951). (281)P. Jannasch & J. Lesinskys Ber. au 2908-2912, (1893). (282)M. Raunert, Piss. Jena (1929). (283)A. Jilek & B. Kohut, Chen. Listy. 21 252-256, (1939). (284)P. Jannasch & A. Rottgen, Zeit. Anorg. Chem. 9, 302, (1895). (285)E. Schulek & S. Floderer, Zeit. Anal. Chem. 202, 388-398, (1934). (286)G. McClellan, J. Assoc. Official Ag. Chem. gh, 726-730, (1941). (287)P. Jannasch & E.V. Cloedt, Her. 994-996, (1895). (288)L. Moser, Book reference (47) page 94. (289)K. Bulan, Zeit. Anal. Chen. 110 697, (1892 ). (290)C. Polstorff & K. Bulcw, Arch. der Pharm. al 298, (1891). (291)T. Rosenbladt, Zeit. Anal. Chen. 260.1548, (1887). (292)P. Jannasch & G. Devi% Ber. 110 2378, (1898). (293)A. EirWrat'cla. Maxymowicz, Zeit. Anal. Chen. 00 14-22, (1926). (294)R. Ripon & C. Gh. Macarovici, Bull. Sect. Sci. Acad. Roumain1 gra 283-294, (1944). (295)A. Outbier, Zeit. Anorg. Chen. 32, 331-339, (1902). (296)J.A. Scherrer, J. Res. N.B.S. 160 253-259, (1936). (297)L. Moser & J. Ehrlich, Ber.1514 430-437, (1922). (298)J. Pattinson & H.S. Pattinson, J. Soc. Chem. Ind. 12,2.11, (1898). (299)P. Wenger & C. Cimermans Rev. Chien. Aeta. ]J., 7V8-143, (1931). (300)L. Moser & A. Brukl, Monateh. 709-'725, (1926). (301)A.L. Kammerer, J. Amer. Chem. Soc. al, 83-98, (1903). (302)A.I. Buseir„ Thur. Anal. Khim. 2, 386-389, (1957). (303)V. Suk, Mast & A. Jenickova, Coil, Czech. Chen. Commun. a, 418.422, (1956). - 205 -

(304) G..Rady & L. Erdef, Zeit. Anal. Chem. 1521 253-258, (1956). (305) A.,Jenickova, V. Suk &14. Haat, Chen. Linty. ,:Z 760-764, (1956). (306) J. Korbi, R. Pribil E. A. EMr„ Chem, Listy. 1440-1444, (1956).- • (307) J. Cifka, PL Malat & V. Suk, Coll. Czech. Chen. Ccinnun. 40 412-417, (1956). (308)Y. Fujita, J. Chem. Soc. Japan Pure Chem. Sec. 22, 615.419, (1956). (309)H..Basimpkat K..Orylska, Chen. Anal. Warsaw. 4J.523-529, (1959). (310)H. Basinska & Z. Orylski„ Chem. Anal.,Warsow.#, 685-690, (1959). (311)A. Singh, J. Ind.•Chem. Soc. 20 473-478, (1955). (312)E. Sudo, J. Chem. Soc. Japan Pure Chen. Sect. Z, 12914294 (1954). (313)104..Nielsch & G. Boltz, Anal. Chim. Acta. 110 438-443, (1954). (314)K.L. Chang, R.H. Bray & S.W. Meleted, Anal. Chem. ao 24-26, (1955). (315)F.B. Martinez & A.P. Bout°, Ind'. Quin. Anal. 9, 86-94, (1955). (316)M. Svach, Zeit. Anal. Chen, J$ 325-328, (1956). (317)14.4. Lisicki & D.F. Boltz, Anal. ChM. irb:i7224724, (1955). (318)N.P. Makukha, .Zhur. KhiM. j Abs. No. 31, 889, (1955). (319)Y. Yamamoto, Japan Analyst. It 513-516, (1959). (320)M. Costing, Nikrochim. Acta, 528-534, (1956). (321)J.A. rean & S.A. Reynolds, Anal. Chim. Acta. 11, 390-395, (1954). (322)M, Ishibashi & T. Fujinaga, Japan Analyst. fo'342-347, (1953). (323)N. Ishibashit T. Fujinaga &. 1..Kusaka, J. Chem. Soc. Japan Pure Chem. sect. 25, 134.4, (1954). . . (324)M.S.jovanovic S.D. Jancovic, Bull. Soc. Chim. Belgrade. uj 119-123, (1955), (325)M.S. JovanOvic,& S.D JancOric, . Soc. Chin. Belgrade. go& 16715, (1937 * (326)DX. B3onbe er, Anal. Chen, 221 1321-1322, (1958)., (327)B. Varimr. Zeit. Anal. Chem. US 425-427, (1958). (328)S.R. E.T. Varkey• Zeit.. Anal. Chen. at, 427429, (1958). (329)I.L. Bagbanly. &I.G. Guseinov, Zhur. Khin. Abe. Do..220 379, (1957). (330) Sotnikov & I.P. Alinarin, Thur. Anal. Min. lho 710413, (1959). (331)P.P. Lott & R.K. Vitek, Anal. Chem. Zs 391-393, (1960). (332)P. Spacu t,S. Calugareanu. An. Univ. C.I. Parton Bucuresti.Ser. Stlints Nat. la, 7548, (1957). (333)A.I. Ousel/ & I. Ivanyatin, Ref. Zhur. Khim. Abe. No. U. 221. (1958). (334)V1. Inhibaehi&T. Matsumoto. Japan Analyst. 343346, (1956). (335)R. Pietch, Zeit. Anal. Chem. 152, 190-192, (1956). (336)L. Vanino & F. Hartl, J. Prakt. Chem. A. 151, (1906). (337)11.4« Wichmann. Ind. ar. Chen. 11, 66, (1939). (338)P. Feta. V. Gentil and P. Goldstein. Anal. Chin, iota, (1953). (339)A. Keechan, Zeit. Anal. Chem. ta, 346-354 (1925). (340)F.C. Edwards & A.F. Voigt, Anal. Chem. at 1204, (1949). (341)T.11. Richarde, J. Amer. Chem. Soc. Zigo 144, (1900). (342)I.N. Kolthoff & tenger. Volumetric Analysis Vol, II. Second Revised Edition. Interectence Publishers. (1947). THE DETERMINATION OF TRACES OF SULPHUR IN ARSENIC AND INDIUM FOR THE SEMICONDUCTOR INDUSTRY

By J. A. CLEMENTS and A. E. PURIM Mining and Chemical Products Ltd., Station Wharf, Alperton, Middlesex

INTRODUCTION DIFFICULTIES encountered with semiconductor devices made from indium arsenide appeared to be due to traces of sulphur in the high purity arsenic and indium used for the production of the intermetallic compound. The determination of traces of sulphur in these metals was therefore necessary. Until recent years the methods used for the determination of sulphur in non-ferrous metals have been insensitive even when working with very large samples. Many of these methods were based on oxidising the sulphur present to sulphate either by a fusion or by treatment with oxidising acids or a mixture of a non-oxidising acid plus an oxidising agent (1-8). The sulphate was then converted to barium sulphate. Another type of method that has been widely used aims at converting the sulphur present to hydrogen sulphide. This can be done for some metals by dissolving them in a non-oxidising acid or more generally by treatment with hydrogen at elevated temperatures(6-16). An alternative method is first to oxidise the sulphur to sulphate and then to reduce the sulphate to hydrogen sulphide with a mixture of hypophosphorous and hydroiodic acids('5' 16). The reduction of sulphate to hydrogen sulphide has also been carried out on barium sulphate precipitates (collected on barium chromate) by heating in a mixture of hydrogen chloride and hydrogen('7). Various methods of estimating the hydrogen sulphide have been used. These are volumetrically with iodine,' 13, 14), colorimetrically as Lauth's violet)'", spectrophotometrically as colloidal lead sulphide6), gravimetrically as silver after precipitation of silver sulphide(11), and gravimetrically after absorption of the hydrogen sulphide-0). Other chemical methods include the burning of the metal in oxygen(18), and the dissolution of metals in copper chloride solutionsw). In the first method the sulphur dioxide is oxidised with hydrogen peroxide and the 509 510 J. A. CLEMENTS and A. E. PURKIS resulting sulphuric acid is titrated with standard sodium hydroxide solution. In the second method the sulphur is separated as copper sulphide and converted to barium sulphate. Physical methods that have been applied to the determination of sulphur in metals include the spectrographic method(20, 21), the mass spectrometric method(22) and the neutron activation method(23). The spectrographic method has a limit of determination of about 50 ppm of sulphur, the mass spectrometric method a limit of about 1 ppm and the neutron activation method a limit of about 10 ppm. The unusually poor sensitivity of the neutron activation method is due to the presence of chlorine in the sample. No application of the polarographic technique to the determination of sulphur in metals appears to have been reported.

EXPERIMENTAL Apparatus Ordinary Pyrex glass apparatus was used for all work. It was cleaned with chromic sulphuric acid cleaning mixture, well washed with distilled water, rinsed with diluted (1 : 1) aqueous ammonia and then washed with deionised water. The polarograph used for this work was the Cambridge Instrument Company's pen recording polarograph fitted with a Univector unit to record derivative polarograms. Reagents Common acids and reagents of AnalaR grade are not sufficiently pure to be used without removal of traces of sulphur. The reagents required free of sulphur for this work were hydrobromic acid, bromine, water, hydrochloric acid, nitric acid and aqueous ammonia. It was necessary to prepare these reagents with sulphur contents of not more than 0.02 The following table shows the results of analysis of available reagents. A and B represent different batches of reagents. TABLE 1

Sulphur pg/m1 Reagent A

Hydrobromic acid 0.20 4.0 Hydrochloric acid 12 < 0.1 Nitric acid 14 21 Bromine < 0.1 < 0.1 Aqueous ammonia 1.0 < 0-1 Water (distilled from glass) 0.11 0.05 Water (deionised) 0.01 0.01 DETERMINATION OF TRACES OF SULPHUR 511 Hydrobromic Acid and Nitric Acid These acids were purified by distillation of the concentrated acid in an all-Pyrex glass still consisting of a 11. round bottom flask, a 500 mm frac- tionating column packed with Raschig rings 6 mm in diameter and 6 mm in length and fitted with a sluice type head. The first 50 ml of distillate was discarded and two-thirds of the remaining acid was distilled. Double or triple distillations were necessary to get acids of sufficient purity.

Hydrochloric Acid Hydrochloric acid was distilled after dilution with an equal volume of water and the addition of a few drops of hydrogen peroxide to oxidise any hydrogen sulphide and sulphur dioxide present.

Bromine Fifty millilitres of bromine was shaken with 10 ml of diluted (1 : 9) nitric acid in a 100-m1 pear-shaped separating funnel, the two phases allowed to separate and the bromine run off into another separating funnel. The bromine was then shaken with three successive 10-ml quantities of water. It was unnecessary to dry the bromine before use.

Aqueous Ammonia This was prepared by passing ammonia gas into deionised water.

Water Deionised water was used throughout except for making the electrolyte, when distilled water was used.

Electrolyte The electrolyte is prepared as follows. Dissolve 20 mg of lead nitrate in 100 ml of water, add 1 ml of concentrated hydrochloric acid and 500 ml of industrial methylated spirit. To this solution add about 1 g of freshly precipitated lead sulphate that has been washed free of soluble salts, dilute the suspension to 11. with water and allow to stand for at least 4 hr before use. The electrolyte is stable for several months. Before use add 1 ml of gelatine solution (0.5 g of gelatine in 100 ml of water) to 99 ml of the electrolyte. Adjust the amount of free lead ion, if necessary, to give a peak height of about 60 mm at one-tenth maximum sensitivity.

Standard Sulphur Solution Standardised sulphuric acid was diluted to give a solution containing 1 mg of sulphur per millilitre. Dilute solutions of sulphur were prepared from this stock solution as required. 512 J. A. CLEMENTS and A. E. PURKIS

METHOD Arsenic To 1 g of arsenic in a 10-m1 stoppered weighing bottle add 1 ml of hydrobromic acid and then a mixture of hydrobromic acid and bromine (1 : 1) dropwise to dissolve the arsenic. Add the bromine slowly to prevent the reaction becoming too violent. Allow the mixture to cool to about 40 °C and shake for 1 min to equilibrate the phases. Heat the solution and then remove the aqueous phase with a transfer pipette. Re-extract the residual arsenic tribromide with 2 x 0.5 ml of hydrobromic acid. Evaporate the combined aqueous phases to dryness on the water bath, add 0.5 ml of hydrobromic acid and again evaporate to volatilise the last traces of arsenic. Dissolve the residue in 1 ml of 0.02N hydrochloric acid, transfer the solution to a 5-ml stoppered weighing bottle, add 1 ml of a 2% solution of 8-hydroxyquinoline in chloroform, stopper the bottle and shake to equilibrate the phases. Add 0.05 ml of 5.75% w/v ammonium acetate solution, shake for 1 min and remove the aqueous phase. Adjust the pH to 9 by addition of diluted (1 : 49) aqueous ammonia and shake the aqueous phase with 1 ml of pure chloroform. Transfer the aqueous phase to a 10-ml beaker and wash each of the chloroform layers in turn with 2 x 0.5 ml of water. Evaporate the combined aqueous layers to dryness on the steam bath, add 0.2 ml of nitric acid and again evaporate to dryness. Dissolve the cooled, dry residue in the electrolyte and dilute the solution to a suitable volume with electrolyte for polarographing. Remove the dissolved oxygen by passing a stream of nitrogen, already equilibrated with the electrolyte, through the solution for 5 min. Record the polarogram from — 0.3 V to — 0.6 V vs. the internal mercury pool anode.

Indium Dissolve 1 g of indium in a mixture of 2 ml of hydrobromic acid, 2 ml of bromine and 2 ml of water, cool the solution to prevent loss of bromine. Evaporate the solution to dryness on a hot plate at 120 °C. Dissolve the cooled residue in 1 ml of hydrobromic acid and transfer the liquid to a 50-mI separating funnel, wash the beaker with 2 x 2 ml of 5N hydrobromic acid. Add 20 ml of methyl iso-butyl ketone and shake the separating funnel to equilibrate the phases. Run the aqueous phase into another separating funnel containing 10 ml of methyl iso-butyl ketone and again shake to equilibrate the phases. Wash both organic phases in turn with 3 x 1 ml of 5N hydrobromic acid. Evaporate the combined aqueous phases to dryness on the steam bath, take up the residue in 1 ml of 0.02 N hydrochloric acid. Complete the determination of sulphur as for arsenic. DETERMINATION OF TRACES OF SULPHUR 513

RESULTS The following table shows some typical results of analyses of high purity indium and arsenic. TABLE 2

Sample Sulphur added Sulphur found Recovery

1 g In — 4 ppm — 1 g In 10µg* 14 ppm 100% 1 g In 10/hg* 15ppm 106% 1g As — 16 ppm — 1 g As 10µg* 27 ppm 104% 1 g As 10/hg* 27 ppm 104% 1g As — < 0.2 ppm — 1 g As — < 0.2 ppm —

* Doping with the standard sulphur solution.

Interference of Some Ions with the Polarographic Determination of Sulphate In all the following tests, the solution containing 10µg of sulphur was evaporated to dryness on the water bath and the residue taken up in the electrolyte. The final volume was adjusted to 10ml.

TABLE 3

Element and Amount added Recovery compound added (rig) of sulphur

B as boric acid 1000 100% B as boric acid 1000 97% P as phosphoric acid 1000 82% P as phosphoric acid 1000 47% P as phosphoric acid 100 112% P as phosphoric acid 100 100% P as phosphoric acid 100 109% Se as selenous acid 1000 Wave obliterated Se as selenous acid (1) 1000 106% Se as selenous acid (1) 1000 100% Te as tellurous acid 1000 Wave obliterated Te as tellurous acid 100 120% Te as tellurous acid 100 123% Te as tellurous acid 10 100% Te as tellurous acid 10 103% Na as sodium chloride 1000 106% Na as sodium chloride 1000 100% K as potassium chloride 1000 100% K as potassium chloride 1000 106% NH4 as ammonium chloride 1000 100% NH4 as ammonium chloride 1000 100%

514 J. A. CLEMENTS and A. E. PURE'S

TABLE 3—continued

Element and Amount added Recovery compound added (Pg) of sulphur

Mg as magnesium chloride 1000 65% Mg as magnesium chloride 1000 62% Mg as magnesium chloride 100 100% Mg as magnesium chloride 100 103% Li as lithium chloride 1000 85% Li as lithium chloride 1000 85% Li as lithium chloride 100 100% Li as lithium chloride 100 100% Ca as calcium chloride 1000 120% Ca as calcium chloride 10 100% Sr as strontium chloride 1000 Peak height increased above pure electrolyte. Sr as strontium chloride 10 64% Ba as barium chloride 1000 Peak height increased above pure electrolyte. Ba as barium chloride 10 '79% Ba as barium chloride (2) 1000 100% Sr as strontium chloride (2) 1000 100% Mo as ammonium molybdate 100 41% Mo as ammonium molybdate 100 35% Mo as ammonium molybdate 10 120% Mo as ammonium molybdate 10 120% W as sodium tungstate 100 100% W as sodium tungstate 100 110% W as sodium tungstate 100 106% W as sodium tungstate 10 100% W as sodium tungstate 10 103% Cr as potassium chromate 100 34% Cr as potassium chromate 100 44% Cr as potassium chromate 10 78% Cr as potassium chromate 10 69% In as indium chloride 1000 150% In as indium chloride 1000 160% In as indium chloride 100 110% In as indium chloride 100 108% Pb as lead nitrate 10 97% Pb as lead nitrate 10 94% Tl as thallium nitrate 50 75%

(1) The solution was evaporated as usual, 1 ml of hydrochloric acid was added and the solution was evaporated to dryness on the steam bath. The treatment with hydrochloric acid was then repeated twice more. (2) The solution was evaporated to dryness as usual, 1 ml of water was added followed by 0.1 g of the ammonium form of Zeo Karb 226 and the solution neutralised to a pH of 7-8 with diluted (1 : 99) aqueous ammonia. DETERMINATION OF TRACES OF SULPHUR 515 The liquid was decanted into a small beaker and the resin washed with 2 x 0.5 ml of water. The combined solution and washings were evaporated to dryness and the determination finished as usual. It was shown that all evaporations of solutions containing traces of sulphur must be carried out at temperatures not greater than 100 °C. No loss of sulphur occurred when solutions containing sulphur were evaporated on the steam bath with water, hydrochloric acid, nitric acid or hydrobromic acid. Standards Aliquots of the standard sulphate solution were evaporated to dryness on the steam bath and the cooled residues were diluted to volume with the electrolyte. For the electrolyte described the relation between peak height depression and concentration is linear over the range 0.2-2 of sulphur. Discussion The oxine separation can often be omitted as materials containing trace metal impurities at levels ten times greater than the sulphur level do not usually interfere. Spectrographic results will reveal whether or not the oxine separation is necessary. For indium samples containing less than 5 ppm of sulphur it is essential to carry out the oxine separation. Elements that interfere and must be guarded against are tellurium, molybdenum, strontium, barium, lead and thallium. The first two elements may be extracted as halide complexes and thus separated from sulphur. The second two elements may be separated by ion exchange as described. The ( last two elements are separated in the general method described. Chro- mium (VI) also interferes but this is easily reduced to chromium (III) which does not interfere. Conclusions A method is presented for determining sulphur in high purity arsenic and indium down to 0.5 ppm on a 1 g sample. (Use of larger samples would enable lower limits to be reached.) Even with a 1 g sample estimation of sulphur contents down to 0.1 ppm can be obtained. Information about the interference of some other ions is given.

REFERENCES 1. THITIENA17ER G. J. Ind. Eng. Chem. 2, 293, 1910. 2. STAHL W. Metalbtirse 13, 414, 941, 1037, 1923. 3. MEIGEN W., and STOCK-SCHROBER K. Zentr. Hfitt. u. Walzwerke 30, 277, 1926. 4. EvANS B. S. Analyst 52, 565, 1927. 5. BULLIVANT D. J. Metal Ind. 60, 271, 1942; and Chem. Age 48, 181, 1943. 6. BERTL&UX M. Ann. Chim. Anal. 28, 44, 1946. 7. BERTIAUX M. Ann. Chim. Anal. 28, 64, 1946. 516 J. A. CLEMENTS and A. E. PITRKIS 8. BERTIAUX M. Ann. Chim. Anal. 28, 152, 1946. 9. JABOULAY E. Rev. Gen Chim. 12, 190, 1910. 10. BASSETT W. H., and BEDWORTH H. A. Trans. Amer. Inst. Mining Met. Eng. 1526. E, 1926. 11. BERTIAUX L. Ann. Chim. Anal. 23, 181, 1918. 12. IssELL H. G. Ind. Eng. Chem. (Anal. Ed.) 4, 284, 1932. 13. BERCOVITCH M. R. Chemist Analyst 25 (1), 4, 1936. 14. SCOTT F. W. Chemist Analyst 31, 52, 1942. 15. SHERMAN M. Amer. Foundryman, 13 (3), 52, 1948. 16. LUKE C. L. Anal. Chem. 21, 1369, 1949. 17. PoLsox D. S. C., and STRICKLAND J. D. H. Anal. Chem. Aeta. 6, 452, 1952. 18. HOLLER A. C., and YEAOER J. P. Ind. Eng. Chem. (Anal. Ed.) 16, 349, 1944. 19. SILVERMAN Louis. Ind. Eng. Chem. (Anal. Ed.) 10, 433, 1938. 20. ROLLWAGER W., and RUTHARDT K. Metallwirtschaft 15, 187, 1936. 21. PFEILSTICKER K. Mikrochim. Acta 358, 1955. 22. HICKAM W. H. Anal. Chem. 24, 362, 1952. 23. ATcrusox Cr. J., and BEAMER W. A. Anal. Chem. 24, 1812, 1952.

DISCUSSION E. MYTUM: (1) Is the method adaptable to the determination of sulphur in different forms of chemical combination, e.g. elementary sulphur and sulphide? (2) What is the standard error of the method? J. A. CLEMENTS: (1) In its present form, no. The method gives total sulphur oxidisable to sulphate. (2) About 10% at the 1 p.p.m. level.