REDUCTION OF CHLORIDE OF SILVER. 55 



Dr. Percy proposes to extract silver from its ores, in the 

 wet way, by means of hyposulphite and chloride of lime. 

 The details of the mode are given in a paper read before the 

 British Association, Aug. 9, 1848. (Ch. Gaz. vii.) 



Solubility of Chloride of Silver. — According to Pierre (Journ. 

 de Pharm. (3) xii. 237), 1 pt. chloride of silver is soluble in 

 200 pts. strong chlorohydric acid, and in 600 pts. of the 

 same acid, diluted with twice its weight of water. 



Reduction of Chloride of Silver. — According to Hornung 

 (Journ. de Chim. Medicale, 1847), moist chloride of silver is 

 easily reduced by metallic copper and ammonia, very little 

 ammonia being required for the purpose. The reduced silver 

 is well washed with water and dried. 



Kessler's method of obtaining chemically pure silver is 

 as follows (Le Technologiste, 1847) : Silver alloyed with cop- 

 per or lead is dissolved in the least possible quantity of pure 

 nitric acid, the solution diluted with 20 times as much water, 

 and a solution of protacetate of iron added as long as a pre- 

 cipitate ensues. The latter is washed first with acetic acid, 

 and then with water acidulated by sulphuric acid, until the 

 wash-water ceases to show a precipitate with prussiate of 

 potash. The precipitation of silver is so complete, that not a 

 trace of it can be found by common salt in the filtered liquid. 

 The protacetate of iron also precipitates platinum, especially 

 by warming the solution. The surface of articles on which 

 galvanic copper is to be precipitated, and which is not easily 

 rendered conducting by graphite, may be rendered so by im- 

 buing it with a solution of nitrate of silver and then treating 

 it with protacetate of iron. 



Wittstein (Buch Rep. vol. ii.) has compared the advantages 

 of the various processes for reducing chloride of silver, and 

 finds that with charcoal to be the safest and most economical. 

 2 pts. of chloride are mixed with 1 pt. of moist charcoal, 

 the whole pressed into a black-lead crucible, loosely covered 

 and heated. Calcination is continued until an half-hour be- 

 yond the cessation of hydrochloric vapor. When cold, the 

 fiilver is extracted by nitric acid of 1.20, 3 pts. being required 



