24 Van Name — Influence of Hydrochloric Acid on the 



and 9 the theory required about 13 cm3 of the decinormal solu- 

 tion, and the excess was consequently 107 cm3 or 0*815 grm. 

 Making due allowance for the large amounts of acid present 

 in these two experiments, the losses are much less than in the 

 preceding ones. 



As the reaction between the bisulphite and hydrochloric 

 acid gives rise to a gaseous product (sulphur dioxide), it would 

 naturally be expected that equilibrium would only be reached 

 when one or the other of the reagents was nearly exhausted. 

 If this is true," the measure of the amount of hydrochloric acid 

 which can be converted into ammonium chloride by a definite 

 quantity of bisulphite solution is the weight of combined 

 ammonia which the latter contains. This value was found to 

 be 0*1757 grm. per cubic centimeter for the bisulphite solution 

 used in the above experiments. This means that if equal 

 quantities of the bisulphite solution and of hydrochloric acid 

 of sp. grav. 1*18 act upon one another, nearly nine-tenths of 

 the acid may be converted into ammonium chloride. It is, 

 however, not necessary to assume that this reaction is complete 

 under the conditions of the experiments of the table. If with 

 a given amount of hydrochloric acid it progresses farther when 

 the quantity of bisulphite is increased, the results are suffi- 

 ciently explained. 



The limit of the reaction between the ammonium sulpho- 

 cyanide and hydrochloric acid is entirely indefinite, but an 

 increase in the amount of this salt must, as in the case of the 

 bisulphite, cause the neutralization of a greater amount of acid 

 and thus briug about a more complete precipitation of the 

 copper. Yery probably, the reduction in the solubility of the 

 precipitate in the acid solution caused by the presence of a\n 

 excess of ammonium sulphocyanide,* also contributes to this 

 effect. 



From these results it is evident that even in strongly acid 

 solutions the copper may be almost completely precipitated by 

 sufficiently increasing the amounts of ammonium bisulphite 

 and sulphocyanide. As far as could be judged from a limited 

 number of determinations made in sulphuric acid solution, 

 the above holds true for sulphuric as well as hydrochloric acid. 

 Cuprous sulphocyanide is, however, somewhat soluble in solu- 

 tions of ammonium salts, and in cases where the amount of 

 acid is very large this may become an important factor. 



The solubility of cuprous sulphocyanide in various solutions 

 is shown in the following table, but the figures must be under- 

 stood to be only approximate. Weighed amounts of cuprous 

 sulphocyanide prepared by precipitation in the usual way, 



* See Table IT, 



