ON THE ELECTROLYTIC METHODS OF QUANTITATIVE ANALYSIS. 299 



VI. — Deposition from Solution of Zinc PhosjyJiate in Potassium Cyanide. 



Moore recommends the precipitation of the zinc from sodium phos- 

 phate solution as rapid and complete. Potassium cyanide is added to the 

 mixture to redissolve the precipitate. Ammonium carbonate is then added, 

 and the mixture electrolysed at 80° C. 



Experiments 1 to 3 show that the precipitation is not complete in 

 two and a half hours. The method cannot be considered rapid. The 

 deposit is firm and bright. On solution in acids a small quantity of 

 carbon remains. 



VII. — Deposition from Solution of Ammonium Lactate and Sulphate. 



Jordis recommends the addition of 5-7 grme. of ammonium lactate 

 and 2 grme. of sulphate to the zinc salt. The solution is acidified with 

 lactic acid, and the hot solution electrolysed in a platinum basin. A 

 mechanical stirring arrangement should be used. The operation lasts 

 about one hour and a half. The author states that when 0-3 grme. of 

 zinc are used the error does not exceed 1 milligramme. 



The following determinations "were made -without a stirring arrange- 

 ment : — 



Conclusions. — Both the methods in which potassium cyanide are used 

 yield too high results and are objectionable on account of the action of 

 the cyanide on platinum. Small quantities of zinc not exceeding 1 deci- 

 gramme can be accurately determined by either of the three oxalate 

 methods or by Brand's pyrophosphate process. For larger quantities of 

 zinc Classen's oxalate process (IV,) in presence of free tartaric acid and 

 Brand's method are recommended. These conclusions agree with Wol- 

 man's > as regards the accuracy of the oxalate methods and the inaccuracy 

 of the Beilstein cyanide process, but differ as to the merits of Brand's 

 pyrophosphate method, which Wolman condemns. Wolman also recom- 

 mends Riche's method, in which a slight excess of ammonia is added to 

 the zinc solution and the mixture acidified with acetic acid, CD. , qq O'l — 0*2 



> Zeits. Electro-Chem., 1897, 3, 540. 



