713 by FERDINAND ACCORDING

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713

XXXVlI.-The Actiou of Dilute Ahera1 Acids on Bleaching Powder.

By FERDINANDKOPFEB, Student in the Chemical Laboratory of 0 wens College.

ACCORDINGto Gay-Lussac (Am,. Chim. Phys., xxvi, 163), bleaching powder contains a mixture or a combination of calcium hypochlorite and calcium chloride, Ca(C10)2 + CaC12. This he proved by obtaining colourless aqueous hypochlorous acid, HOCI, from a solution of bleaching powder, by acidifying with dilute nitric acid and distilling. As soon as it was seen that the old atomic weight of calcium must be doubled, Odling (MaizuaZ, Part I, 56, 1861) pointed out that bleaching powder may be represented by half the above formula, viz. : Ca { Fcl,since this explains as clearly as the old formula the production of hypochlorous acid. The question of the constitution of bleaching powder has recently been again discussed, and Goepner (Polyt. Journ., 209, 204) has made experiments from which he concludes that this substance is to be regarded simply as a compound of lime with chlorine, because in contradiction to Gay-.Lussac’s well-known and generally admitted reaction, he asserts that on decomposition with acids it is simply decomposed into its constituents, yielding chlorine and no hypochlorous acid. To this observation Schorlemmer (Jourtz. Chew. SOC.,xxvii, 335) remarks that Ga y-L ussac’s reaction is certainly correct, inasmuch as Roscoe shows it every year in his lectures, and the laboratory students in Owens College perform it as part of their regular work ; he also observes that he could not con- firm Go e p n e r’s statement as to the non-production of mercuric oxy-

Published on 01 January 1875. Downloaded by Carnegie Mellon University 26/10/2014 13:14:04. chloride when the aqueous bleaching distillate is shaken with metallic mercury. In consequence of these contradictory statements, and as Gay- Lu s s ac’s experiments were merely qualitative, it appeared of import- ance to ascertain the quantity of hypochlorous acid which can be obtained from a given amount of bleaching powder, both from the aqueous solution and from the dry substance. For the purpose of experimenting iipon pure material, dry bleaching powder was prepared from pure slaked lime and chlorine as follows :- First Pwccss.-White marble was ignited in a wind-furnace until free from any trace of carbonic acid. The quick lime thus obtained was slaked with boiling water and kept in a well-stoppered bottle. About 50 grams of the dry powder was placed on a large watch-glass and exposed to a stream of chlorine gas under a bell-jar. The gas was evolved by a mixture of sodium chloride, manganese dioxide and View Article Online

714 KOPFER ON THE ACTION OF DILUTE MINERAL ACIDS sulphuric acid, and had to pass through three wash-bottles before entering the bell-jar. The first of these contained a saturated solution of copper sulphate, the second water, and the third strong siilphuric acid. In some cases the watch-glass mas withdrawn from time to time, its contents thoroughly mixed and again brought into contact with the chlorine gas. The different products of absorption thus obtained were kept in well-closed bottles. Second Process.-For a, second series of experiments chemically pure lime was prepared as follows : a solution of pure calcium nitrate was precipitated by carbonate of ammonia and washed with hot water by decantation. The wet precipitate was placed in a large porcelain dish, and the water expelled by heat. The dry carbonate was then mixed with a, little oil and spread on a firebrick, which was afterwards inserted into a muffle-€urnace. Ignition was continued until all the carbonate had been converted into the oxide. The latter was then partly slaked with boiling water, by which process a mixture of oxide and hydroxide was got, containing 14.42 p.c. of combined water (pure calcium hydroxide, Ca(OH),, contains 24.47 p c.). A few grams of this substance were brought on a watch-glass and exposed as before to a stream of chlorine gas. In order to get rid of the last traces of hydiochloric acid gas present, the gas was finally conducted through a, U-tube filled with small pieces of quick lime. Then it entered the bell-jar by a glass tube, at the mouth of which a watch-glass, containing strong snlphuric acid, was standing in an elevated position sup- ported by a glass tripod. By this arrangement the last traces of moisture were eliminated. A portion of the substance obtained by the latter method was sub- jected to a complete analysis. It was found to contain- 1. Calcium (Ca), 47.6p.c.

Published on 01 January 1875. Downloaded by Carnegie Mellon University 26/10/2014 13:14:04. 2. Total amount of chlorine, 91-96 p.c. 3. Chlorine monoxide corresponding with the hypochlorite present (Cl,O), 13.05 p.c.

Hence its composition is as follows :- Calcium hypochlorite. . 21.46 or, Ca{ g?' ...... 38.12 Calcium chloride .... 1F.69 CaC1,...... 1.03 Calcium hydrate...... 47.52 Ca(@H), ...... 47-52 Calcium oxide...... 13.33 CaO ...... 13.33 -- 100~00 100*00 This shows that Goepner is incorrect in stating that chloride of lime is formed, only when besides calcium hydrate there is hygroscopic water present. The production of chloride of lime from a mixture of View Article Online

ON BLEACHING POWDER. 715 CaO and Ca(OH),, proves that chloride of lime is always formed when there is calcium hydrate present. The following experiments were made with chloride of lime obtained according to the first mode of preparation. About 20 grams of chloride of lime were rubbed together with water in a porcelain Inortar, filtered, and the residue washed with water. From the filtrate 200 C.C.were taken out and diluted up to 1,000 C.C. The amount of chlorine monoxide corresponding with the hypochlorite present was determined by Bunsen’s volumetric method, and data were thus obtained for calculating the quantity of standard acid needed to liberate the chlorine monoxide from the solution, which was to be distilled. In most cases, however, I took a little more than the calculated quantity of acid, because the solution always contains small quantities of caustic lime. For each series of experiments a fresh solution of chloride of lime was prepared. Jfethod of DistiZlation.-A measured quantity of the bleaching- powder solution was taken out by a pipette and brought into a retort. The quantity of acid as above determined, was then allowed to flow in from a Mohr’s burette, care being taken to prevent any local supersaturation, by constantly agitating the contents of the retort. Finally, the mixture was distilled until only a few C.C. were left in the retort. Experiments were made- A. With nitric acid. B. With hydrochloric acid. C. With sulphnric acid. The numbers obtained are found in the appended tables, and the following is the method of analysis employed :-

Published on 01 January 1875. Downloaded by Carnegie Mellon University 26/10/2014 13:14:04. b. C.C. of chloride of lime solution which contain a1grams of chlorine- monoxide (C1,O) as hypochlorite (ascertained by Bunsen’s method) are distilled with n C.C. of + normal acid (1000 C.C. containing + equivalent in grams). The distillate is diluted up to 250 C.C. 1. m1 C.C. of the diluted distillate, to which potassium iodide and hydrochloric acid have been added, require a C.C.of standard thiosnl- phate (1 C.C. corresponding with x grams of chlorine monoxide). Hence the chlorine monoxide A, in the whole distillate amounts to -

250 A, = -a E x, w and as the percentage composition of chlorine monoxide is :-

Chlorine , . . . . . , , . . 81.59 Oxygen . , ...... , . 18-41 View Article Online

716 KOPFER ON THE ACTION OF DILUTE MINERAL ACIDS

A, grms. of chlorine monoxide contain- c1 = '' ' 81*5'' grms. of chlorine. 100

2. nx2 C.C. of the diluted distillate reduced with sodium arsenite solution acidified with nitric acid and precipitated with silver niwate give g grams of silver chloride. From this the quantity c2 of chlorine contained in the whole distillate is found by the following equation- - g x 250 35.4G cz - ~ x- m2 143.46

Supposing now that the distillate is a solution of pure chlorine monoxide, then the following equation must be satisfied :-

c1 = c2 or, ____'2 loo = $31.59. a' TABLEI. A,. Distillation of Solutions of Chloride of Lime after addition of o.lzezfftth Norinnl Nitric Acid

I. 11. 111. IV. v. TI. VII. VIII. IX. ------

50 C.C. of b. p. solution, distilled with n c.c., one-fifth normal HNOB.. , . 22 23 24 25 14.4 15.4 16 16.1 1'7'4

50 C.C. of b. p. SO~U- tion contain chlorine monoxide.. .. *18280.1828 0 -18280 *18%0 *12560 *12560 *12560,1256 0 9256

Published on 01 January 1875. Downloaded by Carnegie Mellon University 26/10/2014 13:14:04. Chlorine nilonoxide obtained in the distillate ...... 1 '1474 0 -15870 -1626 0 *16170 -11300 *11240.1147 0 *lo830 -1083 Chlorine in the distillate calculated fromaz ...... 1 *12030 *1295 Chlorine in the distillate, as found by gravimetric analysis ...... 1 *11890 -1319 View Article Online

ON BLEACHING POWDER. 717

TABLE11. 13. Distillation of Xolutions of Chloride of Lime with one-fifth Nornzal - Hydrochloric Acid. I. 11. - 12 .... 50 C.C. of b. p. solution, distilled with IR. C.C. of ihjdro- chloric acid., ...... 24 24

al .... 50 C.C. of b. p. solut,ion contain a1 grms. of chlorine monoxide ...... 0 *l782 0 -1782 a2.... a2 grms. of chlorine monoxide were found in the distillate ...... 0.1527 0 '1534

c1 *. ,. c1 grms. of chlorine are contained in the distillate; c1 = a2 * calculated...... 0 *1246 0 '1252 100

c2.. .. c2 grms. of chlorine were found to be present in the - distillate by gravimetric analysis...... 0 -1293 0 -1310 C. Distillation of Xolutiort of Chlorida of Lime with orte$fth Normal Sulpplzu~icAcid. 50 C.C.of chloride of lime solution containing A, = 0.3223 gram of chlorine monoxide, as corresponds with the hypothetical hypochlorite, is distilled with 27.9 C.C.of one-fifth normal sulphuric acid, and the distillate is found to contain A, = 0.2401 gram of chlorine monoxide. If we place together the different values of the expression-

cz x 100

a2 Published on 01 January 1875. Downloaded by Carnegie Mellon University 26/10/2014 13:14:04. where c2 denotes the total amount of chlorine as detwmined by gravimetric analysis, and a2 the chlorine monoxide contained in the distillate, ascertained by volumetric analysis, we have for the percentage amount of chlorine in chlorine monoxide the following numbers :- Calculated. Found. A. I. A. 11. B. I. B. 11. 81.59 80.66 83.11 84.68 85.4 Hence we see that in those experiments where nitric was the decomposing acid, the deviations of the numbers found from the calculated results hardly exceed t'he limits of the unavoidable errors of experiment, whilst another proof that the distillates contained no free chlorine is found in the fact that, when tested qualitatively with silver nitrate, they invariably remained quite clear, whereas the presence of View Article Online

718 KOPFER ON THE ACTION OF DILUTE MINERAL ACIDS the smallest quantity of free chlorine would have been at once recog- nised by the immediate formation of silver chloride according to the equation- C1, + 2AgNOA -!- H20 = 2AgC1 + 2HN03 + (3120. In the case of the experiments with hydrochloric acid these deviations, however, became considerable, and the distillate yielded a distinct turbidity with silver nitrate. Here, then, the distillate was a mixture of relatively much chlorine monoxide with little free chlorine, and it is easy to ascertain the proportion of the chlorine monoxide to the free chlorine present! from the numbers given under B I and 11. B I, 6.18 pts. of free chlorine to 78.5 pts. of chlorine as monoxide or to 96.21 pts. of monoxide. B 11, 7.62 pts. of free chlorine to 77.78 pts. of chlorine as monoxide, or 91.31 pts. of monoxide. The quantity of acid taken for these experiments, moreover, most probably exceeded the quantity needed to saturate the caustic lime and to liberate all the chlorine monoxide, giving rise to the evolution of chlorine. With regard to the purity of the chlorine monoxide obtained by the experiments A 111-IX, inclusive, and GI, I contented myself with a qualitative test. The different distillates underwent no change after addition of silver nitrate, thus showing that no free chlorine was present. Assuming that the distillates in all experiments consisted of a soh- tion of pure chlorine monoxide only, which assumption is of course not quite correct as to the experiments with hydrochloric acid, we may compare the different values of the expression-

a2 x 100

611 Published on 01 January 1875. Downloaded by Carnegie Mellon University 26/10/2014 13:14:04. which, if all the chlorine monoxide had distilled over would be = 100, for al denotes the chlorine monoxide corresponding with the hypochlorite contained in substance taken, and a2 the quantity of chlorine monoxide obtained in the distillate. I. 11. 111. IV. V. VI. VII. VIII. IX. A. 80.63 86.82 88.95 88.45 69-97 8949 91.32 86.23 89.04 13. 80.08 80.17 c. 74.5 In the most fnvourable case (A VII) 91.52 per cent, of the chlorine monoxide corresponding with the hypochlorite contained in substance taken, was obtained in the free state by distillation. The reason why this number, and still more the others, deviate so considerably from 100, is owing to the fact that chlorine monoxide is lost during distil- View Article Online

ON BLEACHING POWDER. 710

lation, especially during the first period, when the nionoxide which passes over is comparatively concentrated, and is already partly decomposed into chlorine and o,xygen (Gay-Lussac) thus :- 2c1,o = 2c1, + 0,. This chlorine cannot be condensed completely, even when the mouth of the condenser in the receiver dips under water. During the begin- ning of the distillation of even highly dilute solution of bleaching powder with aqueous acid a distinct smell of clilorine was always perceptible, thus showing that chlorine was escaping. Still it appeared of interest to repeat the foregoing experiments and to determine quantitatively how much chlorine was actually lost by distilling a bleaching solution after addition of the quantity of acid exactly required to decompose the hypothetical hypochlorite and to saturate the caustic lime. W olt er s (J.pr. Chem. [el, x, 128 ; abstract, Chem. Xoc. J., xxviii, 237) has recently stated that freshly prepared solution of bleaching powder treated with acids, at first liberates chlorine only, and that the small quantities of chlorine monoxide which are found in the distillate, besides free chlorine, mainly arise from a secondary reaction of the free chlorine upon the calcium salts formed, e.g. :- Ca(NO& + C1, + H20 = CaC1, + 2HN0, + C1,O CaS04 + Cli + HzO = CaC1, + HzS04 t C120.

In order to eliminate this possible source of error, hydrochloric acid was used as the decomposing acid in the following experiments, and in order to obtain very favourable results, a filtered solution of freshly manufactured bleaching powder was prepared and completely anaIysecl. It contained in 1,000 C.C. :-

Published on 01 January 1875. Downloaded by Carnegie Mellon University 26/10/2014 13:14:04. Grams. 1. Calcium...... 10.752 2. Available chlorine ...... 17.736 Or chlorine monoxide, corresponding to the hypochloride ...... 10.869 3. Total amount of chlorine...... 18.042

As 10.176 grams of calcium correspond with the total amount of chlorine, there is 0,576 gram of calcium present as hydroxide Ca(OH)2. The quantity of acid needed to liberate the chlorine monoxide from 1 C.C. and to saturate the caustic lime is 0.27863 C.C. of normal acid. By several preliminary experiments the conclusion was arrived at, that 25 C.C. of the above solution, when diluted with about 200 C.C. of water, and then distilled with the required quantity of acid, namely View Article Online

720 KOPFER ON THE ACTION OF DILUTE MINERAL ACIDS

34.83 C.C. of one-fifth normal hydrochloric (or about that) gave the best results. The following table does not need further explana- tion :- TABLE111.

I. i 11. 111. IV. -

25 C.C. of solution distilled with C.C. of one-fifth normal hydrochloric acid ------34 -6 --34 '8 25 C.C.of b. p. solution contain chlorine monoxide...... 0 b2717 0 *2717 0 -2717 0 '2717 ------Chlorine monoxide obtained in the distillate...... 0 -2473 0 -2499 0 '2504 0.2516 ------__- -- -- Chlorine monoxide left in the retort. , . - 0 *0035 0 *0036 0.0030 ------Chlorine in the distillate calculated from the amount of CI2O found in the distillate ...... 0 '2017 0 *2039 0 *2043 0.2053 ------Chlorine in the distillate, as determined by gravimetric analysis...... 0 *2079 0 '2050 0 *2083 0 '2119 ------Chlorine contained in the residue de- --r- termined by gravimetric analysis ... 0.4792 0 *.a710 0 *4802 0 -4677 ------c2 + c3...... 0 -6871 0 '6760 0.6885 0.6796 -- Total amount of chlorine contained in 0 $978 25 C.C.of b. p. solution + chlorine contained in C.C. of acid employed 0.6971 0 ' 6964 0 '6978 ------n -~1 Loss of chlorine c, - c during distillation...... 0 -0107 0 '0211 0 '0079 0 *0182 Published on 01 January 1875. Downloaded by Carnegie Mellon University 26/10/2014 13:14:04. If we place together the different value of- c2 x 100

where c2 denotes the total amount of chlorine as determined by gravimetric analysis, and ctz the amount of chlorine monoxide contained in the distillate as ascertained by volumetric analysis, we have for the percentage amount of chlorine in chlorine monoxide- Calculated. Found. . A \ I. 11. 111. IV. 81.59 84.07 82.Q3 83.18 84.22 Assuming as before, that the distillates consisted of a solution of pure chlorine monoxide only, we may compare the different values of the expression- a2 x 100 View Article Online

ON BLEACHING POWDER. 721

(which, if all the chlorine monoxide had distilled over, would be = loo), for al denotes the chlorine monoxide corresponding with the hypochlorite contained in the substance t'aken, and a2 the quantity of chlorine monoxide obtained in the distillate. Calculated. Found.

A r -I I. 11. 111. IT: 100 91.02 91.98 92.16 92.57 Although the deviations of these numbers from 100 are almost as considerable as in the foregoing experiments, the reason for this is readily understood. In the first place, some bleaching substance was always left in the residue, which when calculated for C1,O gave the number u3,as found in the table. Comparing the values of the expression- aR . 100 a1 giving the amount of chlorine monoxide left in the retort in per cents. of that originally contained in solution taken, we have- I. 11. 111. IT. - 1.26 1.28 1.09 Secondly, in each distillation a certain amount of chlorine monoxide is lost as chlorine, and this amount (found in the lowest column of Table 111) when calculated on the percentage of total chlorine-monoxide contained in substance taken, gives the following numbers :- I. IJ. 111. IT. 4-82 9.52 3.5 7 8.21 and these, although very irregular, indicate a distinct loss of chlorine

Published on 01 January 1875. Downloaded by Carnegie Mellon University 26/10/2014 13:14:04. in each case, and explain the fact that the distillate contains on an average about 8 per cent. of chlorine monoxide less than the amount corresponding to the hypothetical hypochlorite contained in the substance taken. Experiments were next made on the distillation of weighed quantities of dry bleaching powder after the addition of acids :- D. With nitric acid. E. With hydrochloric acid. Method of 7XstiZZatio?z.-8 granis of chloride of lime containing al grams of chlorine monoxide were put in a porcelain mortar, and 91 C.C. of normal acid added, flowing in a fine stream out of a Mohr's burette. The mixture was meanwhile constantly stirred to prevent local supersaturation. The solution thus obtained was washed into a retort and distilled, the distillation being continued until about 10 C.C. were still left in the retort. View Article Online

722 KOPFER ON THE ACTION OF DILUTE MINERAL ACIDS

Distillate diluted up to 250 C.C. 1. ml C.C.of the diluted distillate, after addition of potassium iodide and hydrochloric acid, require a C.C. of standard hyposulphite (1 C.C. corresponding to x grams of chlorine monoxide) ; hence the whole distillate contains- 250 a' = -ax 131 1 chlorine monoxide in grams, containing-

c1 = '' 81'59 grams of chlorine. '100

2. ?nz C.C. of the same diluted distillate reduced with sodium arsenite and precipitated with silver nitrate, yield g grams of silver chloride ; hence the whole distillate contains :- 250 c2=- .g.- 35*46 grams of chlorine. m2 14346 In the case of the distillate being a solution of pure chlorine monoxide, the equation- c = c2 must be satisfied. For experiment D I and 11, material was used as obtained from the second preparation. The bleaching powder employed in D I contained 14.3 per cent. of chlorine monoxide, corresponding to the hypochlorite present, and the material employed in D I1 was that analysed on page 714, containing 13.05 per cent. of chlorine monoxide whereas the material employed in E I was the first preparation as described on page 713, and contained 22.26 per cent. of chlorine monoxide.

Published on 01 January 1875. Downloaded by Carnegie Mellon University 26/10/2014 13:14:04. D. Distillation of Dry Chloride of Lime after addition of + Normal Nitric Acid (1 C.C. = 0.063 gram HNO,). s. n. al. 1 a2. m,. . x. m2. g. -- -- ~ --~- --- 'I. 1 '4162 2'7 -17 0 *20250 -1422 50 13 '35 .00213 100 0 *1898 0 '11736 0 *1160

11. 2.554'7 51-92 0.33340.2834 50 26'58 -00213 I The distillate of Experiment I1 was tested qualitatively only by silver nitrate, when it underwent no change.

E. Distillatiorh qf Dry Chloride of Lime with 6 Normal Hydyochloric Acid. 0.4862 gram of substance distilled with n = 33 C.C. of b normal View Article Online

ON BLEACHING POWDER. 723

hydrochloric acid yielded in the distillate cz = 0.0775 gram of chlorine monoxide, whereas the calculated amount was 0.1082 gram. The distillate when tested by silver nitrate gave no turbidity. Here we have- L12 * 160 a1

I. 11.

----__I- D ...... 70'17 85.00 E ...... 91-84 -

That is to say, the distillate in the most favourable case was found to contain 85.00 per cent. of the chlorine monoxide, corresponding with the hypochlorits contained in substance taken. That the distillate in Experiment D I consists of a pure solution of chlorine monoxide is shown by the fact that the quantity of chlorine contained in it is found to correspond with the chlorine monoxide as determined volume- trically, or- Found. Calculated. c2 * 100 = 82.54 81-59 2 The results of the foregoing experiments may be summed up as follows:-If to a solution of bleaching powder, or to the same substance in the dry state, a dilute mineral acid, such as nitric, hydrochloric, or sulphuric be added in such quantity as to saturate the caustic lime and to decompose the hypochlorite supposed to be present according to Gay-L us s ac's hypothesis, then on distillation, an aqueous Published on 01 January 1875. Downloaded by Carnegie Mellon University 26/10/2014 13:14:04. solution of almost chemically-pure chlorine monoxide is obtained, which amounts in the most favourable case to about 92 per cent. of the chlorine monoxide as corresponding with the hypothetical hypochlorite. And, therefore, as the chemical constitution of a substance is always deduced from its mode of formation and from its products of decomposition obtained by the action of the weakest possible reagents, we may state that : Bleaching powder either contains calcium hypochlorite, besides calcium chloride, or a compound of the constitution- Ca { ::'. a kind of double salt in which calcium is combined with two different acid radicals. Both views explain equally well the production of hypochlorous acid, View Article Online

724 KOPFER ON THE ACTION OF DlLIJTE MINERAL ACIDS

and both account in a satisfactory manner for the formation of bleaching powder by the action of chlorine upon calcium hydroxide. One atom of chlorine first replaces the group OH, which combines in the nascent state with the hydrogen atom of another hydroxyl to form water, whilst the second atom of chlorine must replace that hydrogen atom. Further, the views of Gay-Lussac, as well as of Odling, account for the non-production of bleaching powder from anhydrous lime, whilst it is difficult to explain this fact if bleaching powder is supposed to contain a compound of chlorine and calcium oxide. Indeed from the analysis on page 714 it is clear that if the compound CaOCl, really exists in bleaching powder, it cannot contain water, inasmuch as anhydrous lime is present, in the mixture. But upon what grounds do Go e pner and W o 1t er s base their conclusion that bleaching powder contains a compound of the empirical formula CaOCI,, which they state to be resolved by acids, under all circumstances, into its constituents, namely, free chlorine and lime ? Go e pner arrives at this conelusion from the fact that when bleaching powder was distilled with small quantities of hydrochloric or sulphuric acid, he failed to detectl hypochlorous acid in the aqueous distillate by the so-called Welters'* reaction. Wolters, however, admits that by distilling solutions of bleaching powder with so much nitric or sulphuric acid as corresponds with the hypothetical hypochlorite present, the caustic lime held in solution preventing the acid from being in excess, he always found in the distillate small quantities of aqueous hypochlorous acid besides free chlorine. This he ascribes to the action of chlorine upon the calcium salts formed, as I have already mentioned, and to the action of the chlorine upon the compound CaOCl,. The former source of error was obviously entirely eliminated in my experiments Published on 01 January 1875. Downloaded by Carnegie Mellon University 26/10/2014 13:14:04. with hydrochloric acid ; but supposing that by acting as above with dilute hydrochloric acid upon bleaching powder first, only half of the quantity of the compmnd CaOCl, is decomposed, thus :-

and considering that by my experiments with hydrochloric acid more than 92 per cent. of the chlorine monoxide (as corresponding with the hypothetical hypochlorite present) was obtained in an almost chemically pure state by distillation, the conclusion is arrived at that the formula- CaOC1, + C1, = CaCl, + C1,O 8 An aqueous solution of hypochlorous acid, when shaken with mercury, yields brown oxychloride of mercury, whilst free chlorine produces calomel only. This reaction, which is generally said to hare been recently discovered by Wolters, was a well-known fact as early as 1849, when it is mentioned in Gmelin’s Handbook. View Article Online

ON BLEACHING POKDER. 72 5 represents the chief reaction, which takes place when the compound CaOC1, is acted upon by chlorine. But this reaction entirely decides the question in favour of Odling’s view with regard to the constitution of the compound CaOC1,: for-

That chlorine really liberates hypochlorous acid from bleaching powder is a well-known fact, which was first proved by Gay- Lussac, and has since his time been frequently confirmed by experiment. Hence we see that by assuming the existence of tlhe compound CaOC1, in bleaching powder, and by even admitting the decomposition of that compound with mineral acids to consist in the liberation of chlorine under all circumstances, we are still led to the conclusion that it must have the constitution which Odling has assigned to it. But I have every reason to doubt the truth of the above reaction, v1z. :- 2CaOC1, + 2HC1 = CaOCI, -f- CaC12 + C1, + HZO for I observed the following phenomena :- 1. During the careful addition of the quantity of dilute mineral acid exactly sufficient to saturate the caustic lime beld in solution, and to decompose the hypothetical hypochlorite, or half the quantity of compound CaOCl, present, not the slightest smell of free chlorine is given off, but only the characteristic smell of hypochlorous acid. 2. When the mixture obtained according to 1 is shaken in the cold with a large excess of mercury, brown oxychloride is formed in quantity, thus showing the presence of free hypochlorous acid.

Published on 01 January 1875. Downloaded by Carnegie Mellon University 26/10/2014 13:14:04. Hence by far the more probable theory is that the hypochlorous acid, or rather the chlorine monoxide, is a direct product oE the action of hydrochloric or other dilute acids upon bleaching powder, and that therefore either Gay-Idussac’s or Odling’s view is to be adopted with regard to the chemical nature of the essential constituent of bleaching powder. Which of the two views gives the true constitution of the compound cannot be decided by my experiments, but from a paper by Mr. Charles Kingzett, which has recently been read before the Chemical Society, it would appear that Gay-Lussac held the right view, as Mr. Kingzett states that he has obtained cryst,als from a cold saturated solution of bleaching powder by evaporation in a vacuum, or by the action of intense cold, which on analys‘is were found tg be calcium hypochlorite, a compound never previously isolated. ___-

VOL. XSVIII. 3D