713 by FERDINAND ACCORDING

View Article Online / Journal Homepage / Table of Contents for this issue 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 Scho rlemmer (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 super- saturation, 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., .................................

Load more