DETERMINATION OF MAN$ ANESE AS SULPHATE AND B$ THE SODIUM BISMUTHATE METHOD

By William Blum

CONTENTS

Im n u m n n s m n ns 1 . porta ce of acc rate a ga e e deter i atio u s in v m m s 2 . So rce of error gra i etric ethod ur s in v u m m s 3 . So ce of error ol etric ethod

THE B IS M UTHATE METHO D . Ou tline of m ethod

H st m t . 2 . i ory of e hod n n z n s u . 3 . Sta dardi atio of ol tio (a) Discu ssion o f m ethods ‘ (b) Evidence b ased o n redu ction and reoxidation P n m s and s u ns 4 . reparatio of aterial ol tio

(a) Water .

(d) Potassiu m perm anganate

(f ) Stab ility of perm anganate solu tions

(g) Manganou s su lphate .

(h) Sodiu m ox alate . s— b (i) Ferrou s su lphate solu tion Sta ility .

(j) Nitric acid .

(k) B ismu thate . . ‘ (l) F erric nitrate (m ) Use of weight b u rettes Standardiz ation of perm anganate with sodiu m ox alate Standardiz ation of perm anganate With manganou s sulphate (a) Standardi z ation of m anganou s su lphate solu tions (b) Efie ct of conditions u pon the standardiz ations with m anga nou s su lphate

- ( 1 ) F errou s su lphate permanganate ratio . m n m n n i m n (2 ) A ou t of a ganese prese t n a deter i ation . v u m m s n n (3 ) Acidity , ol e , ti e of ta di g , etc (4) Use of phosphoric acid (0) Prob ab le cou rse of reactions mm (d) Conditions reco ended . Agreement of valu es derived from sodiu m ox alate and m anganese su lphate Analysis of pu re permanganate crystals

Analy sis of m anganese ores . mm Su ary . B u lletin of the B u reau of S tandards [VOL J

I. INTRODUCTION

1 P C C C $ . IM ORTAN E OF A URATE MAN ANESE DETERMINATIONS

In spite of the large number o f methods in use for the deterrnina , hi e ff nd tion of t s important element , r sults by di erent methods a i i diff erent chem sts seldom show satisfactory agreement . Wh le differences of as much as a f ew per cent of the manganese present have little commercial significance in iron and steel containing 1

o f ur per cent or less manganese , the highest possible acc acy is demanded in the analysis of high - grade materials such as manga Of hi un nese ore and ferromanganese , w ch large amo ts enter into m at co merce , prices dependent upon the results of analysis . For exam e 1 1 1 m, imports of manganese ore by this country in 9

n 1 8 2 1 1 86 1 6 . amou ted to 7 5 long tons , valued at $ 79 It can readily be seen that a constant error of 1 per cent in the analyses of such material may cause a considerable diff erence in the total amount paid for the ores . That constant errors of such magni tude are possible with our present methods will be shown in this paper .

C OF IN $ V C H 2. SOUR ES ERROR RA IMETRI MET ODS

Even with the greatest care the gravimetric results are not

r o f necessarily accu ate , due not alone to the possibilities losses by solubility of precipitates ; and o f too high weight due to con tam inatio n from vessels or reagents ; but also to uncertainty in f the composition o the precipitates as weighed . The three forms in which manganese is most commonly determined gravimetri Mn M P Mn m 0 n O O . cally are 3 4 , , z 7 and S 4 It is generally ad itted r o f f that the fi st these is unsatis actory , as the composition depends directly upon the temperature o f the ignition and the nature o f e r the atmosphere surrounding the precipitat . Even unde care 1 fully regulated conditions Raiko w and Tisch l<1o w could not

2 obtain results which agreed to better than 1 part in 0 0 . $ ooch

1 t 3 5 . em . Z . xo r 1 1 r. Ch g , , p 3 ; 9 3 m .) Determination of M anganese and Austin 2 have shown that the composition of manganese pyrophosphate depends upon the content of ammonium salts and ammonia , and the temperature , volume , and method of pre ti cipita o n of the manganese ammonium phosphate . Even under “ o hi i in the conditi ns w ch they recommend , the r errors amounted s 1 o f ome cases to per cent the manganese present , and were in hi t e . r gen ral too gh The me hod can not , therefore , be conside ed f r hi n satis acto y for ghly accurate work , and certai ly not for obtaining a known amount of manganese to serve as a primary standard . Experiments described in this paper have led to i the conclusion that manganous sulphate , obta ned under proper

$ n r hi i co ditions , is the most accurate fo m in w ch th s element can be weighed , both in gravimetric analysis and in securing a known

o f a amount mang nese .

O E OF ERROR IN V L C M ETHODS 3 . S URC S O UMETRI

The difli cu lty of securing a known amount of manganese to serve as a primary standard has hindered the accurate investigation of the great number of volumetric methods which have been pro r posed . In most cases they have been tested by compa ison with r methods , gravimetric or volumet ic which had not been shown to hi u r . be int insically accurate T s fact , together with the us al de pendence o f the results of such methods upon the precise conditions of operation , has led to the publication of a large number of contra i to r d c . y papers upon these methods For example , the Volhard method and its various modifications has been the subject of over

0 i 5 investigations since its publ cation in 1 8 79 . It is generally admitted that the results by this method are low unless an em irical ndi p factor dependent upon the co tions of operation , is em

re ployed , though some investigators have obtained theoretical lt un f su s d . V o der certain con itions In iew the above situation , it is highl y desirable to find some method which will yield results o f knownaccuracy , which are not closely dependent upon the exact o f hi r conditions operation , and w ch may se ve to test other methods .

’ Am i . 6 . . Sc . 2 18 8 . J , , p 33 ; 9 -

B u lletin. o th e B u reau o tandards o 8 f f S [V l .

THE B IS M U HA E M E H II . T T T OD

1 L H . OUT INE OF MET OD

Of various methods considered , the bismuthate appeared most f i promising , and has been ound to entirely fulfill the above requ re ments . In this method the manganese in nitric acid s olution is o f oxidized with sodium bismuthate , which the excess is removed by filtration through asbestos . To the resulting permanganic

o f f r acid is added a measured excess e rous sulphate solution , which is then titrated with permanganate of known strength f and of known ratio to the errous solution . The investigation therefore resolved itself into a study o f the methods of standardiz ing the permanganate employed in the final titration and the influence o f the various conditions o f operation upon the results obtained by the bismuthate method .

2 H $ H . ISTOR OF MET OD

The method as originally prepared by Schneider 3 depended upon the use o f bismuth tetroxide as the oxidizing agent and titra dr tion o f the permanganate acid with hy ogen peroxide . In this 4 f Cam re do n 5 orm the method was employed by p , Mignot and s Reddro 7 di jaboulay . p and Ramage mo fied it by employing hi di f f sodium bismuthate , w ch was more rea ly obtained ree rom r chlorine , and suggested filtration of the pe manganate acid di On o f rectly into the hydrogen peroxide . account the instability 3 o f the latter reagent Ibbotson and B rearley replaced it by ferrous i n h i f ammonium sulphate , w ch orm the method has been since 9 B di f o r used , being described in detail by lair , whose rections this hi method are generally followed in t s country .

3 P 269 2 1 888 D l . 2 . i . . . ng o y J , , p 4 ; 4 h 6 1 8 8 R ev im Ind u st 9 . 0 . . C . , p 3 ; 9 5 Ann h im al 5 1 2 1 0 0 . C . An , p . 7 ; 9 . 5 R e v en c im 6 1 1 1 0 . . g . h , p . 9 ; 9 3

7 m 6 7 68 1 8 . e . S o c . . 2 . J Ch , , p ; 9 5 8 w 84 2 1 0 1 . em . N e Ch s , , p . 47 ; 9 9 i I o h and th e d and em ical al t . . Am . em . S o c. 26 . ; 190 4 r , 7 J Ch , , p 7 93 Ch An ys s of on 9 Determina tion of M anganese

3 Z . STANDARDI ATION OF SOL UTION — (a) Discu ssion of Meth ods As above stated the accuracy of any such volumetric method depends principally upon the method of i B 1° standard zation employed . lair mentions in his book three f methods , viz , (a) calculation rom the iron value , (b) use of a steel o f o f un o known content , and (c) use a known amo t of mangan us f sulphate , without expressing any pre erence , or opinions as to di their relative accuracy . Standardization by means of so um oxalate may be included under (a) since values found with t his standard under proper conditions 11 have been found at this B ureau to agree with iron values within 1 part in Method (b) is a secondary method and is evidently unsuitable f o r work of high accuracy . As will be shown later , the standardization of manganous sulphate is a tedious operation and subject to co nsid l erab e errors . For this reason sodium oxalate was considered at this B ureau to be the most convenient and accurate standard hi B 13 f o r . t s method rinton , however , stated that there was a diff erence o f 1 per cent (at first stated as over 3 per cent) between the values based upon sodium oxalate and manganese sulphate , f m B Dr H respectively . In a paper ro this ureau by . W . F . ille 14 brand and the author the reasons fo r our belief in the accuracy of the sodium oxalate standard were expressed in the form of a o f hi preliminary paper , the conclusions w ch have been verified by subsequent investigations described in this paper . b i i i i — ( ) Ev dence Based on Redu ct on and Reox dat on . The orig inal basis o f our use o f the sodium oxalate standard f o r this method was the fact that if a definite amount of a permanganate solution be reduced and then reoxidized by means o f the bismuth it ate method , is exactly equivalent in oxidizing power to the original permanganate . This experiment was based upon a

° 1 di i 0 B lai e c mm e d th e ta d a diz a i wit dium xal a In th e a e dix of th e 1 1 2 e . e pp n 9 t on , p 3 3 , r r o n s s n r t on h so o t , u d e a xi m atel th e c d iti ive b M cB ri d e as th e m t accu ate m et d a c clu i b a ed n r ppro y on ons g n y , os r ho ; on s on s c ed in a e u pon th e work d es rib this p p r. 11 m c 34 1 2 M cB rid e : . Am . e . S o . . 1 r . J Ch , , p 4 5 ; 9 13 See B u eau of ta d a d e ti cate ib l e I O re ta d a d am le 2 . r S n r s C r fi for S y ron , S n r S p 7 13 Ind n m 3 2 and 6 1 11 . . E . e . . . J g Ch , , pp 3 7 3 7 ; 9 14 . Ind . En . em . 3 . 1 1 1. J g Ch , , p 3 74 ; 9 ° — 73 764 1 3 8 B u lletin o the B u reau o S tandard f f s [Vo l . 8 similar one suggested by Wolff 15 and employed by de Koninck

e n f o r for t sti g the accuracy of the Volhard method manganese . Its significance as applied to the bismuthate method is that the manganese is oxidized to the same state o f oxidation as was origi MnV H nally present in the permanganate , theoretically . In the absence o f evidence to the contrary it seems highl y improbable that any appreciable manganese can be present in a filtered per n - ifa a manganate solution in a form other t n , and still less proba b le that in an entirely diff erent medium the manganese shoul d be

e o xidatio n o th er oxidiz d by bismuthate to the same state of , \ than V H Mn e e B . S ince , how v r , at least two persons in addition to rinton had observed a discrepancy o f the order o f 1 per cent between the um l a e sodi oxalate and manganese su ph te valu s , the subject de serve d further inve stigation ; not alone from the standpoint o f the

e e e hr n mangan se d t rmination , but also as possibly t owi g light upon the composition o f permanganate solutions and their action

e n e e as oxidizing ag nts . At this poi t it may be m ntion d that the original obser vations regarding the reduction and re oxidation o f

h e e a e ee r e re t p rmangan t have b n confi m d enti ly , with solutions A

B $ e 2 2 . , E and , pr pared as shown on page 7

PR PA AL AND L N 4. E RATION OF MATERI S SO UTIO S — (a) Water. Water used in the purification of permanganate and in th e preparation o f all the permanganate solutions except I

K wa e h e e and s distill d t r e tim s , the last two being from alkaline

e IV ater e f o r r p rmanganate . us d the rest of the work was o dinary distille d w ater o f good grade . 6 r — T f ( ) Ai . he air used to deliver the solutions rom the stock bottles was washe d with acid bichromate solution and alkaline permanganate followe d by a column o f glass wool . — (c) Asb estos The asbestos used in the filtration of the per

e manganat solutions and in the bismuthate method , was digested

e w d e for s veral days ith hy rochloric acid , which was finally r moved was by thorough washing with hot water . It then suspended in water and the finest portions separated and used in this work . x e For a f ew o f the e periments this asb stos was ignited , without

‘5 15 1 8 . 6 . el . im . B 1 0 B ul l . So c. ta l u Ei e 11 . 1 8 1 . g , , p 5 ; 9 4 S h s n , , p 3 73 ; 9 Ch Determination of M anganese

a ff l m king , however , any appreciable di erence in the resu ts . A $ 2 - B w inch platinum cone , arranged as suggested by lair, as used

for preparing the filter . — (d) Potassiu m Permanganate . Two commercial samples of o a B n’ p t ssium permanganate were employed , aker and Adamso s ’ “ ” Kahlb au m K C . . s . P salt , and grade A portion of the former

‘ was purified by two recrystallizations in Jena glass flasks , the l solutions being electrically heated , and fi tered through ignited

$ asbestos just before being allowed to crystallize . The fine crys tals so Obtained were sucked dry on a platinum cone and were then exposed in a thin layer in the dark for four weeks in a vacuum n dessicator over concentrated sulphuric acid , the vacuum bei g 2 Of . S dr maintained at approximately cm In pite this long y ing , the material was found to contain per cent water as deter mined b y heating to decomposition and collecting the water in a

weighed calcium chloride tube . When dissolved in pure water and f immediately filtered through asbestos , the solution le t a slight stain l upon the fi ter . After thorough washing this stain was dissolved o ff with sulphurous acid , and its manganese content determined

e . colorimetrically , being equal to about per cent , i . , a negli N gib le quantity . umerous attempts to prepare a permanganate solution which would leave absolutely no stain upon asbestos

proved unsuccessful . Whether such stains were due to the action lf Tsch eishvili 18 of the asbestos itse as claimed by , or to reduction of the permanganate by traces o f dust or other reducing sub

. un n stances , could not be determined The amo t of such reductio was , however , negligible , and far less than that observed by h i h ili Tsc e s v . (e) Permanganate Solutions were prepared by dissolving a weighed amount o f the salt in water ; and in t h e case o f the com m ercial e samples , filtering through asbestos to r move manganese

peroxide , etc . They were then made up to a definite weight of

solution , since the subsequent analyses were conducted entirely

with weight burettes .

17 13 42 m o c. Ru . P . e . . 8 h emical nal i of th cd . . 1 2 . J . hy h S , , p 6 1 10 . C A ys s Iron , 7 , p 3 ss s C 5 ; 9 ll t n o th B u r u o tanda 8 B u e i f e ea f S rds [ Vo l .

The following solutions were employed in the i nvestigation : TAB L E I

Permanganate S o lutio ns Used

Approxim ate strength KM n0 4 P reserved

P u rifie d

B 85 A O rdinary

Kahl b aum

These solutions were preserved in stock bottles provided with an inlet and exit tube with ground glass joint as in an ordinary

was - gas wash bottle . To the inlet tube sealed a U tube containing

o f was some the same solution as in the bottle , thereby preventing changes in concentration of the latter . The exit tube was pro — vided with a three way stopcock and a tip by which the solution could be delivered to the weight burette by means of purified compressed air . — (f) Stab ility of Permanganate Solutions At first it was thought necessary to protect these solutions with black paper , but later experiments showed that in the co urse o f several months no appreciable decomposition took place l n the solu tio ns exposed ff f f to di used daylight , provided they were first reed rom peroxide and were protected from dust and other reducing substances , f . o r and that only purified air entered the bottles Solution I , f example , prepared rom ordinary distilled water , and permanga nate containing appreciable peroxide , which was removed by a hr ff e single filtration t ough asbestos , did not su er d composition within the limits o f observation ( 1 part in 2 0 0 0 ) on standing f o r two months without protection from the light ; even though it was intentionally exposed to bright sunlight f o r several hours soon

f . w a ter it was prepared In connection ith this observation , 19 o f which simply confirms previous work others , it is desirable

° 1 H n n e 18 1 8 6 $ a d e and N rt o c em Ind e ki a k em . 0 : . M a d W l : Am . . . 1 . r . S . . ors , op s r Ch J , , p 4 ; 9 n r o h J Ch , ' i i i P 0 23 . 1 . a a m 6 0 n i nd T ch eish v l : . . 6 1 W sk s s 8 . p 9 ; r . , 59 9 4 y J Ch hy , , p 5 7 ; 9 E la m] Determina tion of M anganese 72 3 to call attention to another point in connection with the stability h as en of permanganate solutions , which so far as I know not be U di previously noted , or published . nder con tions which rapidly f na . o reduce neutral permanga te solutions , e . g , the presence dust, i IS reducing gases , or precipitated peroxide , decomposit on greatly m retarded by the addition of a small a ount of alkali . It was upo n r i the basis of this obse vation , first noted qual tatively , that Solution 1 o f B was prepared with per cent potassium hydroxide . Results f with this solution were entirely satis actory , but since the other er solutions , when protected from reducing substances , were p fe ctl o f u u y stable , the use alkaline sol tions for this work was fo nd U ar . i unnecess y nder commercial conditions , however , where it s not always practicable to protect the solutions , the addition of a f small amount o alkali will add to their stability . — (g) Manganese Su lph ate . Pure material was prepared from 30 0 ’ gr ams of Kah lb au m s crystallized manganese sulphate Zur

the operations being conducted entirely in platinum . It was dissolved in water and filtered to remove a small amount of insoluble matter . It was next saturated with hydr ogen u h sulphide , prod cing a small amount of a black precipitate whic di was found to contain copper . Ad tional hydrogen sulphide and o f a small amount ammonia produced a precipitate entirely pink ,

hi . w ch was filtered out The hydrogen sulphide was expelled , a few drops of sodium hydroxide were added and the solution was f r boiled and filtered ; the precipitate being ound to contain i on .

This last operation was twice repeated , the third precipitate being f f f . o ni m free rom iron An excess pure , reshly prepared ammo u ‘ o f MnC h carbonate was then added and the precipitate OS was ed with hot water , by decantation and suction , till free from sulphate . It was dissolved in a slight excess of hydrochloric acid and crystal

' liz ed i MnCl 11 0 at tw ce as , , 4 2 ( The latter crystals were

w o f e treated ith an excess sulphuric acid , and heated in a doubl walled platinum dish till almost al l the excess sulphuric anid was expelled . The product was entirely soluble in water , and con tained a slight excess o f Sulphuric acid as determined in sa bse en s qu t te ts (Table II , A , p . B u lletin o the B u rea u o tandards o 7 2 4 f f S [V l . 8

h S diu m Oxa te — hi ( ) o la Two samples were employed , one w ch h ad been especially purified by the author for a previ ous investiga 20 e hi B tion , and a larger sample pr pared especially for t s ureau , f and which was ound to have a reducing value equal to the former , i f in 2 0 0 0 within the lim ts o 1 part .

(i) Ferrous Sulphate and ferrous - ammonium sulphate were employed indiscriminately after it was found that the solutions C possessed about the same stability . The . P . salts as purchased d n o t were employe , since their exact composition was important . N u r . For use with pe manganate , the sol tion was prepared

B r - according to lair , with g fe rous ammonium sulphate (or g crystallized ferrous sulphate) and 5 0 cc concentrated sulphuric N er . u se acid p kilogram of solution For with permanganate , a solution containing g ferrous - ammonium sulphate (or g ferrous s ulphate) and 5 0 cc concentrated sulphuric acid per kilo

If r . eco m gram was prepared phosphoric acid was employed , as 21 D f o f mended by udley , it replaced hal the sulphuric acid in the N solutions ; but was added in addition to the regular amount N of sulphuric acid in the solutions . — S tability of th e ferrou s su lphate s olu tion Incidental observa tions upon the change in strength of N ferrous ammonium i h e sulphate ind cated that t rate of oxidation , though slow , was o f erratic , due no doubt to variation in the extent its exposure to N f ni air . With ferrous sulphate and errous ammo um sulphate , the daily rate o f oxidation under the conditions used was appro xi

1 r 0 0 . e . 1 mately pa t in 5 , i , about per cent in five days , over con i ra le hi s de b periods . T s rate will depend no doubt upon the con ditio ns o f di of its preservation , and is interest only as in cating how often its strength should be checked up f o r work o f any desired f u ni degree o acc racy . Ratios obtained at the begin ng and end of various series o f determinations showed that no appreciable change

o f f ew n r took place in a period a hours , thus co fi ming the observa $ 2 tion o f B askerville and Stevenson

P . (j) Nitric Acid o f regular C . grade was employed ; in the con centrate d f 2 orm , and diluted to 5 per cent and 3 per cent by vol

20 4 m c . 3 2 m e . o . 1 1 1 2 . B lu m : . A . S J Ch , , p 3 ; 9 21 B lair: emi cal al i I th ed . . 1 2 . Ch An ys s of ron , 7 , p 5 22 m em c 3 3 1 1 1 1 1 . A . . S o . . 0 . J Ch , , p 4; 9 Determination , of M anganese

ume . The former two solutions were preserved in the dark,since it has been recently shown by Reynolds and Taylor 23 that nitric 10 m b t reco m acid as weak as per cent is deco posed by light , u that laC bination takes p e in the dark . — k B is t t . P u e . ( ) m ha Two samplesof C . sodium bismuthate were f B f employed , one rom aker and Adamson and one rom Eimer and diff . a Amend These two samples ered very markedly in appe rance , f . o f the ormer being dark brown , and the other yellow In spite hi ff t s fact , no di erence could be detected between them as regards their suitability for this oxidation . It is well to mention however ni that this compound , of more or less indefi te composition , is if six somewhat unstable , and preserved for over months should be ffi tested fo r its e ciency of oxidation . — (l) Ferric Nitrate In order to test the effect of ferric salts upon a o f this method , it was necess ry to obtain iron , or some salt iron hi t which was free or practically free from manganese . T s proved o diffi be a cult task , and after testing American ingot iron , and a o f f and f f large number errous erric salts , the only one ound satis ’ f a o f r actory was sample Merck s c ystallized ferric chloride , which contained less than per cent manganese . To convert this to r o t nitrate , it was fi st converted t sulphate by evapora ion to the o f appearance fumes with an excess of sulphuric acid , and the di sulphate was precipitated with ammonia , washed and ssolved in nitric acid . The resulting salt was free from chloride (of which traces interfere in the bismuthate method) and contained only a w ff small amount of sulphate (which is ithout e ect on this method) . m i B — ( ) Use of We ght u rettes. Simple weight burettes were made by drawing down the tips o f cylindrical graduated separa tory funnels (50 and 10 0 cc) The increased accuracy gained by the use o f weight burettes is especially desirable in an operation n involving a back titration , and also the ratio of the two solutio s

o f used . Weighings were usually made to g , except in the case o f ul the smaller amounts manganese s phate solutions , which were

1 . weighed to 5g or in some cases 0 . 0 0 g The titrations were rl mm usually made in E e eyer fl asks o f convenient size .

33 101 1 1 2 J . Chem . S oc. , , p . 1 3 ; 19 7 2 6 B u lletin of th e B u reau of S tandards ( Vo l . 3

Z P $ W H DIU $ L 5 . STANDARDI ATION OF ERMAN ANATE IT SO M O A ATE

“ N hi th e McB ride ot ng is to be added to conclusions of , except to th e emphasize their relation to present problem . The conditions recommended by h im for the standardization of N perman ganate are briefly as follows: Volum e o f 2 5 0 cc ; acidity 2 per cent ° 80 sulphuric acid by volume ; initial temperature , to slow ni addition of permanganate , especially at begin ng and end ; final temperature not less than and end point correction by com “ parison with a blank containing a known amount o f the perman

anate Hi r g . s statement that the variation in results ove a wide

1 10 0 0 range of conditions does not exceed part in , applies to

o f 0 N titrations involving the use about 5 cc of permanganate . If N C , however , permanganate , ommonly used in the bis m u th ate method , is standardized with sodium oxalate , slight variations in the conditions may cause a relatively much larger if as 2 error , especially is not uncommon , only about 5 cc of per di N rm manganate is employed . For standar zation of pe an

anate di McB ride g , the con tions of were employed , except that the

f 0 . n o . e co nce initial volume was 7 5 cc instead 25 cc , i , the oxalate tratio n fo r N r was about the same as pe manganate . In this way the uncertainty in the end point caused by titrating in a large

u to i . volume with weak permanganate , can be red ced a m nimum ur o For acc ate work , however , the end point correcti n should be o f hi rm made , since the object t s titration is to dete ine the absolute

o f O o f oxidizing power the permanganate . With S small a volume ° ° solution$ it is usually necessary to reheat it to 60 to 70 before i McB ride completing the titrat on . These conditions , as shown by , ni o f e . represent a mi mum consumption permanganate , i . , the iron

or manganese values are a maximum . Any deviation from these hi conditions will tend to lower the iron or manganese values , w ch it is believed accounts in part f o r the discrepancy noted by B rinton a rid others between values derived from sodium oxalate and from o f manganese sulphate . For calculation the manganese value

f d f . rom the so ium oxalate , the actor was employed

3 4 1 . Am . em . So c . 4 5 ; 19 1 2 . J Ch , p Determina tion of M anganese

Z OF P $ W H $ 6 . STANDARDI ATION ERMAN ANATE IT MAN ANOUS SUL PHATE — (a) Standardiz ation of Manganou s Su lph ate Solu tions The two methods commonly used f o r determining the strength of a manganous sulphate solution are (a) precipitation as manganese b ammonium phosphate and ignition to pyrophosphate , and ( ) evaporation of the solution and heating the residue to a certain U o f temperature . nfortunately both these will yield high results if the solution contains substances other than manganese sulphate ; whether in the original salt or derived from the glass in which the B u solution is preserved , t even with pure solutions the results o f ro h o s are of uncertain accuracy , especially in the case the py p

1 w phate as above mentioned (p . 7 Weighing as sulphate as therefore adopted as a means o f securing a known amount of u manganese . The chief source of ncertainty here is the tempera

u o f t re the final heating , a point upon which the evidence is rather 25 uncertain and contradictory . Volhard was able to obtain B constant weight with a special burner , but not with a unsen “ ar 2 o f burner . M ignac determined the atomic weight manganese “ ’ by heating the sulphate nearly to red h eatf Meineke 27 deter ul f mined this element as the s phate , which a ter being heated to a temperature not stated , was completely soluble in water . Fried 8 ° heim 2 heated the salt to 3 60 to while $ ooch and Austin 29

o 1 obtained constant weight by heating in d uble crucibles , cm reco m apart , the outer one being at red heat , a procedure since ”0 mended b y Treadwellfi In determining the water o f crystz alliz a i r n tion of the var ous hyd ates of manga ous sulphate , Thorpe and 3 ‘ 3 2 ° ° Watts heated the salt to L inebarger to 1 70 to 1 80 and 3 3 ° ° Cottrell to 2 70 to 2 80 though the latter fdund that no deco m position took place at 3 50 Richards and Fraprie 3 4 showed how a 1 H f ever that as much s o . per cent , O remained in the salt a ter

35 nn 19 - 3° 11 A . em 8 18 6 8 e n l u a t l . Hal . a s i . 10 . 1 . T eadw ll a d : Ch , pp 3 3 4; 79 r $ n An y s , , p 4 ” 5 c 1 31 8 . et N at 0 2 88 em 3 7 . 1 1 1 Sc . . . 3 ] , p . 5 ; 1 3 . . . So c. , ; 80 . Ar h i phys [ J Ch , p 3 37 em 9 32 m em 15 2 2 . Zt . 1 8 1 8 188 . A . . 18 . Ch g , , pp . 47 , 7 7 ; 5 Ch J , p . 5 ; 93 33 8 33 4 Z a al em 8 . 68 em 1 . . . 18 P . 6 00 . n Ch , , p 7 ; 99 . J . hys . Ch , p 3 7 ; 9 39 “ Am . 5 . 20 8 26 . . Sci , , 9 ; 189 . Am . em . p . ; 190 1 J p Ch J , 75 7 2 8 B u lletin of the B u reau of S tandards

heating for one half hour at but that five minutes heating ° 0 at 45 produced complete dehydration without decomposition . 3 6 C a 3 5 B l ssen and lair recommend heating to dull red ; while. 7 Freseniu s 3 declares that accurate results can be obtained onl y by e ul chance , as it is impossible to expel all xcess s phuric acid without

decomposing the salt . The following experiments were conducted to determine the temperature to which manganous sulphate may and must be water heated , to expel all the or excess sulphuric acid and to

i . 2 obta n the normal anhydrous salt About g of the . salt was heated in an open platinum crucible in a small electrically heated m u flle , temperatures of which up to were measured with a ° ° 0 - filled 0 0 45 nitrogen thermometer , and above 4 with a platinum B rhodium thermocouple calibrated at this ureau . The crucible was kept covered in the desiccator and upon the balance , where r it was weighed against a similar crucible as a ta e . The results

of three series of heatings are shown in Table II , the figures in the last colum n being calculated from the weight which remained ° practically constant from 45 0 to

TAB L E II

Temp erature o f deco mp o sition o f mangano us sulphate A

M n n u s ul e re red a on 723 ( a ga o s phat p pa s p . )

T empera T im e Weig t P er ce t of h of n Rema k ° r s h u e ( C ) (hou rs) M nS O ¢ (g) constant weight

Slight d arkening

35 37 e F e iu - : u a al i 2 Au s ew . M et . d . n al i c e m . . 6 . e h $ . , , . 9 . g , r t p 7 h A y t s h n Ch , I p 3 3 s n s Co n n An ys s I 35 m e . al si of I o th ed . . 1 2 6. Ch An y s r n, 7 , p ' Determina tion of M anganese 7 2 9

T h e final ' product was dissolved in water , and the insoluble e Mn 0 residue filtered out , wash d and ignited , yielding g 3 4,

i r 1 M e u u O . eq valent to g Mn , o g S 4 The filtrat was

f o r B evaporated series .

T empera ° tu re ( C ) (hou rs) M n8 0 4 (g) stant weight

Slight d arkening D ecid ed d a e i rk n ng.

H O H O A few drops 2S 3 + 2S 4 were added to the final product , which was then reheated for series C .

P er cent of con stant weight

i Sl ghtd arkening .

D ecid ed darkening .

From Table II the following conclusions may be drawn : ( 1) Manganous sulph ate does not undergo any appreciable decomposition upon prolonged heating to temperatures up to ° ° ( 2) At temperatures from 5 50 to 60 0 (from incipient to dul l s s s l o n redne s) thi alt decomposes slow y . (3) The anhydr us ormal salt can b e obtained Only by heating for considerable periods a t ° 450 to 50 0 especially if an excess o f sulphuric acid be originally n i presen t. (4) Attempts to obtain the pure salt by heati g d rectly

over a flame , or even in a double crucible , without temperature e regulation or measurement , must be subject to considerabl r unce tainty . Having now a means for obtaining a known weight of mangan f ous sulphate , solutions of known strength ( rom to g manganese per g of solution) were prepared by dissolving a known ° 0 weight of the pure salt , heated to constant weight at 45 to to o f and making up a definite weight solution , the manganese

o f Mu content which was calculated by the use of the factor SO4 = 6 r 8 . Mn o . 3 3 In one case , for example , g pu e anhydrous

Mu SO4 was dissolved in water and the solution made up to exactly

10 0 1 0 g ; producing a solution g of which contained g Mn , which value was confirmed by evaporation of a weighed portion ° $ Determ i of the solution and heating to 47 5 to constant weight . nations made by another chemist upon this solution , by evapora ” f o r ul tion and heating a short time to d l redness , yielded the

2 0 2 2 1 0 2 10 1 values 9 , 3 , and ; the mean value

f o f 1 r being there ore per cent too high , i . e . an error about pa t 2 0 U in 5 . pon another solution prepared in the above manner , and containing g Mn per solution , the same chemist obtained by direct heating to dull redness 2 0 0 6 and 2 0 0 5 ;

o f f i . e . the results were high , in spite the act that in the latter series at least , very slight decomposition had evidently taken place in the bottom of the crucible . Apparently therefore those parts of the salt on the sides of the crucible had not been heated to the necessary temperature for a sufficient length of time to expel all water or excess acid . In view of these facts , the desirability o f s substituting for the manganous sulphate , some other tandard , such as sodium oxalate , is very evident . (b) Effect of Conditions upon Standardization with Manganous — S F erro u s s u l h ate- erm an anate ratio s ulphate p p g Thi ratio , f o f which is undamental for the accuracy the method , is usually o f r determined by means a blank experiment ; that is , a dete mina

e tion is run through in the absence of mangan se , under the con di i n t o s . to be used in the regular analyses This procedure , which was evidently devised fOr the purpose o f eliminating errors due to

B u lletin of th e B u reau of S tandards — (2 ) Am ou nt of m anganese present in a determination One of the serious limitations of this method is the small amount of manganese generally determined , making it somewhat unreliable i B for h gh grade materials . lair recommends the presence of from n to g Mn , involvi g the use of a sample of manganese ore

1 of only g , obtained by taking an aliquot of the solution of g B 3 9 of the ore . Ibbotson and rearley state that the method is equally applicable for large or small amounts of manganese with hi out , however , giving the evidence for t s conclusion . Since with

N 1 0 . 0 0 . 0 1 s 3 permanganate , 5 Mn the largest amount that can be mi conveniently deter ned , the following experiments were con

1 N KMn e ducted with approximately 0 . O, and F SO The resul ts are expressed l n terms of the manganese value of 1 g o f the per manganate solution . It should be noted that a high result indi

o f cates incomplete oxidation the manganese by the bismuthate . In these and the following series the following conditions were tentatively employed , and the variation produced by a ch ange of di i o f one con tion was noted in each ser es experiments . The manganese sulphate was oxidi zed at room temperature in a 0 n 2 volume of about 5 cc , containi g 5 per cent nitric acid by volume . An excess of bismuthate (about g) was added , the was solution agitated for one minute , the sides of the flask were 0 o f rinsed down with 5 cc 3 per cent nitric acid , and the solution at once filtered with suction through the asbestos filter , previously coated with bismuthate . The flask and filter were washed several

o f hi 1 times with 3 per cent nitric acid w ch about 0 0 cc was used . f The filtration and washing required rom one to three minutes . To the filtrate ferrous sulphate was added immediately in slight

t . excess , which was at once ti rated with permanganate

39 2 w 8 . 2 6 1 . em . N e 0 0 Ch s , , p 9 ; 9 Determination of M anganese

TABL E III Effect of Amo unt of Manganese in th e Presence o f V ariable Am o unts o f Iro n

KM nO, Solution I

M anganese valu es calcu lated from m anganou s su lphate

V alu e d etermined over a $ ram mangane e 1 g kM II0 4 lu ti n s s s $ rams iron present so o period or th ree weeks present

From Table III it is evident th at fo r amounts of manganese up a to g the method is accurate within the limits of error , i . e . bout 1 0 0 o . 10 part in 5 , while results obtained with as much as g Mn

’

- are decidedly erratic , only one half approaching the correct values .

It is apparent therefore , that about 5 g Mn is the practical limit di un under these con tions . This amo t is , however , far more satis factory than only g , and permits the use of g of a high grade m nganese ore , a decided advantage . As seen in s s B o erie A and , the results with as much as 3 g ir n present , are B u lletin o th e B u reau o S tandards 8 73 4 i f [Vo l .

f o f entirely satis actory . The agreement the sodium oxalate and manganese sulphate values will be discussed later

A cidit V olu m e Tim e o S tandin eta — T (3) y , , f g , he results of sev eral series o f experiments to determine the eff ect o f vari ous condi tions upon the bismuthate method are summarized in the follow ing table : TABL E IV

Eff ect o f C o nditio ns up o n Bism uthate Standardiz ation KM ( nO4 S olution K)

1 2 34 110 4 s lu S eri e s M ethod M odification 3 = o t10n g M n

d d 26 a a . 7 . St n r , p d d 2 a a . 73 St n r , p .

I i ial c c. E N O 10 er ce n t on a, p nt I i ial c c E N O 40 er ce n t on . g, p nt Ini ial v lu m e 150 cc t o , Shak en with b ism u thate 15 s ec Stood b efore fil tration 10 m in Stood b efore filtration 30 min Stood after filtration 10 m in Stood after filtration 20 m in t Stood af ter filtration 30 min d af e ad d i i of F e S O m in too t r t on ; 10 . tood after ad d ition of F eS O 4 30 m in — Ad d ition of H3P 0 4 5 cc

i d ean of all M u s o l valu es except C 1 and H2

Of th e Mu O e S 4 valu s given in Table IV , the individual deter m inatio n o f all H 1 s except those in C 1 and 2 varied less than part

0 0 f ul in 5 rom the mean , showing that accurate res ts can be obtained o f f over a very wide range conditions . The only conditions ound to produce appreciable errors were (a) deficiency o f nitric acid and (b) allowing th e solution to stand more than 1 0 minutes after the

o f f r o f 1 0 addition the er ous sulphate , which about cc excess was

f o r o f present . Since there is no occasion either these conditions

e e e ur to aris in good practic , the m thod may be considered acc ate un e o f d r all ordinary conditions procedure , an important criterion

o f for a standard method analysis . — (4) Use of P h osph oric Acid The addition o f this reagent as ‘ reco mm ended b D f y udley , was ound convenient though not nec r N s ffi essa y , since with olutions there was no di culty in obtain Determination of M anganese 73 5

u ing a sharp end point within cc of permanganate , witho t its ul u l . u use If used , it sho d be added to the ferro s s phate solution f n be orehand , rather tha during the titration , since in the latter case a white precipitate , probably consisting of basic bismuth

di . phosphate separates , rendering the end point slightly less stinct — With very large amounts of iron , e . g . 3 5 g , such as would have Mn to be used if in steel were determined with N permanganate , it was found that addition o f phosphoric acid possesses no advan e tage , since it t nds to produce a pink color , due probably to the 4 f o f 0 ormation an acid ferric phosphate , which obscures the end point as much as does the ferric nitrate . The use of N solutions is therefore recommended only for manganese ores and similar

- ur high grade products , in which the highest acc acy is desired . 0 b b e C u se e cti ns — ( ) Pro a l o r of R a o From Table IV, some light may be thrown upon the probable course of the reactions when manganese is oxidized by bismuthate . At least two reactions are probable (a) direct oxidation to MnVII and (b) interaction of MnII MnVII MnIV i unoxidized with the , precipitating , which s then removed from the oxidizing influence of the bismuthate . If a these two re ctions may take place , the problem resolves itself into a determination o f the conditions under which reaction (a) will be accelerated and (b) will be retarded , so that (a) goes practically t to completion before (b) can take place to an appreciable ex ent . The favorable conditions for (b) as conducted in the Volhard method , for example , are slight acidity and high temperature ; ’ ul which sho d therefore be avoided in the bismuthate oxidation . That this explanation is plausible is shown by a comparison of ff C and C . That complete oxidation may be e ected in a short R fo time is indicated in I in which connection the necessity g

. O thorough agitation must be emphasized ther experiments , not

o . 0 co m letg recorded here , showed that with 5 g or more of Mn , p oxidation could not be effected if the solution was not thoroughly s s agitated . In the earlier experiment in thi investigation , the solutions were artificially cooled to about b ut after it was ° 20 2 found that results at room temperature , to were entirely f a . satis ctory , artificial cooling was dispensed with

4° lenme er and Heinric : Ann. em . 190 . x 1 : 18 . Er y h Ch , , p 9 77 ° 73 764 - 13 9 B u lletin o the B u reau o tandard ' 8 f f S s [ Vol . — (d) Conditions Recommended. C orrect results can be obtained under the following conditions : To the manganese solution co ntainmg 20 to 40 per cent nitric acid (free from nitrous acid) in

0 1 0 a volume of 5 to 5 cc , add a slight excess of bismuthate (usually

hl - 0 . 5 to g) , agitate thoroug y for about one half minute , wash ni down the sides of the flask with 3 per cent tric acid , filter through 1 0 0 s asbestus , wash with cc of 3 per cent nitric acid , add a light o f ul excess ferrous s phate , and titrate at once with permanganate . as B For iron and steel , N solutions described by lair are satisfactory . For ores and ferromanganese N permanganate solution may be employed , and an amount of material containing about 5 g manganese . For the rapid solution of ores , a method recommended 41 ne by B lair has been found convenient . O g of the ore is fu sed in

10 l 1 a large platinum crucible with g potassium bisu phate , g of di sodium sulphite and o . 5 g so um fluoride . The heating should r v f be very slow till eff e escence ceases . A ter complete fusion the ul 10 product is cooled , then heated caref ly with cc concentrated di sulphuric acid , cooled , ssolved in water , and made up to a u l definite volume . The slight precipitate of bari m su phate

usu ally present will not influence the manganese determination .

$ N VAL U D IV D DIUM $ L AND 7 . A REEME T OF ES ER E FROM SO O A ATE MAN$ ANOUS SUL PHATE TABL E V

m so n o f Na C 0 and Mus a s C o pari 2 2 4 O4 v lue

M anganese valu es d erived from

Sodium oxalate M anganese su lphate

= D = D eterminations 1 g KM nO 4 g M n eterminations 1 g KM n0 4 g M n

41 P riva t e comm u ni ca tion . Determination of M anganese

Consideratio n of the values in Table V shows plainly that no greater diff erence than 1 part in 50 0 exists between the results s derived from the odium oxalate and manganese sulphate , respect ivel s 1 c as y , instead of the former value being per ent lower , i B . o 1 claimed by r nton and others In fact in the case of the . N s o hi 1 nt solution , the nly ones in w ch an accuracy of more than pa

0 0 s s s s in 5 is realizable , the manganou ulphate value how a tendency to be from one to two parts per thousand lower than the sodium oxalate results . It is at least interesting though perhaps not s o f ignificant , that if the value 5 instead 3 be used for the o ul s at mic weight of manganese , the res ts with the N solution agree in every case to within 1 part in 10 0 0 .

N L $ I PUR P N$ N $ L 8 . A A S S OF E ERMA A ATE CR STA S

Additional evidence of the correctness of the above values was found in the analysis of the pure permanganate prepared as

2 1 described on page 7 which contained per cent water . The s s o alt hould therefore c ntain per cent manganese , instead of M K nO . per cent , the theoretical content for pure anhydrous 4 This difl erence with specially purified permanganate indicates clearly the probable presence of water as well as manganese

C . . u peroxide in P permanganate , rendering it uns itable as a m was mi pri ary standard . Manganese deter ned gravimetrically by p recipitation with ammonium sulphide ; the manganese sul hide hi p being washed with dilute ammonium sulp de , ignited in a su l h ro u s s weighed crucible , treated with p and ulphuric acids , ‘ ° e 0 a vaporated , heated to 45 to constant weight , and weighed s Mn O . S 4 The manganese in the filtrates was determined colori metrically . Results of duplicate analyses were per cent and

per cent , the mean per cent agreeing closely with the

o f theoretical value 3 per cent . The oxidizing value this o f A A permanganate was determined by means solutions 1 , 2, and hi o f E (Table V) w ch were prepared by the solution an exact weight , 4 A A o f . of the salt in a definite weight solution In I and 2, exactly

I KMn 1 g O, was dissolved and diluted to kg ; yielding solutions having an oxidizing value equivalent to per cent Mn (average o f ul f o r all sodium oxalate and manganous s phate values AI and i B 8 73 8 B u llet n of the u reau of S tandards [ q .

A2) . Solution E contained g of the salt per kilogram , and s di Mn posse sed an oxi zing power equivalent to per cent , (derived from the average of all sodium oxalate and manganous B s . s $ K sulphate values for olution E) Solution , , I , and were prepared of only approximately the desired strength , and the results have no relation to the composition of the solid permanga nate employed .

N L $ I N$ N 9 . A A S S OF MA A ESE ORES

Analyses of the B ureau of Standards Manganese Ore (Standard

N . 2 Sample o 5) by means of permanganate I , gave as the average ni t Mn of ne determinations , per cen upon the basis of the um d di sodi oxalate stan ar zation , and per cent if calculated

- r ul from the manganous sulphate . These es ts are in good agree 6 de ermi ment with the mean value 5 6 . 3 per cent derived from all t nations upon the certificate , and with the value formerly di found by the author with the bismuthate method , using so um f oxalate as the standard . Un ortunately comparisons based upon this sample are not necessarily conclusive , since the mean value per cent is derived from results ranging from to obtained by eight chemists using a variety of methods , the lack of s agreement of which is illustrated . If the bismuthate result by the author are correct , a conclusion made highly probable by the th e work here described , value of the ore lies between and per cent manganese ; and many of the values found by other

‘ methods , by the author and others are too high . That the tendency of many commercial methods is to yield results higher t t m han hose by the ethod here recommended , is shown in the results of analyses of three manganese ores by the author and two well known commercial chemists . TABL E VI

Analyses o f Manganese Ores

Analyst M ethod O re I O re II O re III

di c e M o fied a etat . B ismu thate