48 REPORT — 1853. 



On a New Method for determining the Amount of available Chlorine con- 

 tained in Hypochlorites of Lime, Soda or Potash. By Astley Paston 

 Price, Ph.D., F.C.S. 



Numerous as have been the methods proposed for determining the available amount 

 of chlorine in bleaching powder and other hypochlorites, there is not one that I am 

 acquainted with by which correct and expeditious determinations can be made. The 

 following method is based on the known reactions of hypochlorites of lime, potash or 

 soda, and hypermanganate of potash, on arsenious acid, the former of which reactions 

 has, as is well known, been frequently proposed as the principle of many ingenious 

 chlorimetric processes. The application of hypermanganate of potash to the estima- 

 tion of iron and other substances having been attended with such good practical results, 

 I am led to anticipate that the extension of its application to the estimation of chlorine, 

 in the manner hereafter described, may tend to simplify the manipulations, and curtail 

 the time now requisite for determining the commercial value of the hypochlorites in 

 the several conditions in which they are met with and employed in the arts. The first 

 point to be attained, in the correct estimation of bleaching powder, is to effect complete 

 solution without endangering a loss of available chloi'ine. This may be effected by 

 weighing a given quantity of the specimen under examination into a large flask, and 

 adding a normal solution of arsenite of potash or soda in such quantity that an excess 

 be always present, and after dilution with water, gradually pouring in during agitation 

 an excess of hydrochloric acid. A normal solution of arsenious acid is obtained by 

 dissolving 139-63 grs. of arsenious acid, corresponding to 100 grs. of chlorine, in a so- 

 lution of potash or soda, and diluting the solution with water to 1000 measures. If 

 50 measures of this normal solution be measured into a flask, and after dilution with 

 ■water be acidified with hydrochloric acid, and to it be carefully added from a graduated 

 burette a solution of hypermanganate of potash until the solution acquires a decided 

 pink colour, the value of the solution of hypermanganate of potash will be obtained, 

 as the number of measures employed will correspond to 5 grs. of chlorine. Having 

 obtained a normal solution of arsenious acid and a standard solution of hypermanga- 

 nate of potash, the commercial value of the hypochlorites of lime, potash or soda may 

 be most easily determined. 100 grs. of the bleaching powder under examination are 

 placed in a flask graduated to 1000 measures; 500 measures of the normal solution 

 of arsenious acid are then added, and after dilution with water hydrochloric acid is 

 gradually poured in until a slight excess has been employed. The solution is then 

 made up to 1000 measures. If 100 measures of this solution be now transferred into 

 a large flask, and after dilution with water, a standard solution of hypermanganate of 

 potash be gradually added from a burette until the solution assumes a distinct colora- 

 tion, the number of measures employed will indicate the amcmt of arsenious acid re- 

 maining unchanged into arsenic acid, which quantity being deducted from the amount 

 of arsenious acid originally employed will give the proportion of available chlorine 

 contained in the sample of bleaching powder. Thus supposing that 10 grs. of bleach- 

 ing powder had been employed, and that 50 measures of the normal solution of arse- 

 nious acid, corresponding to 5 grs. of chlorine, had been added, and that 30 measures 

 of the standai-d solution of hypermanganate of potash, corresponding to 3 grs. of chlo- 

 rine, had been necessary to transform the excess of arsenious into arsenic acid, then 

 the 10 grs. of bleaching powder would have contained 2 grs. of chlorine, or the value 

 of the specimen would be 20 per cent. 



Instead of employing 1 00 grs. of bleaching powder, and proceeding as before men- 

 tioned, any number of grains may be taken, — 30 grs. I have found to be a very con- 

 venient quantity, — which being placed in a flask, a known quantity of the normal 

 solution of arsenious acid is added, and after dilution with water, a clear solution is 

 obtained by the addition of hydrochloric acid. To this a standard solution of hyper- 

 manganate of potash is added, and from the number of measures employed the value 

 of the sample under examination is determined. With a small amount of practice, 

 the estimations may be made in a very expeditious manner, and the results obtained 

 I have hitherto found to be most satisfactory. 



In the estimation of the commercial value of the hypochlorites of potash or soda, 

 the amount of available chlorine will be indicated in the same manner, and with the 

 same degree of accuracy, as the determination of the value of bleaching powder. 



