86 FED SILVER ORE. 



nitric acid, and the silver and the antimony separated 

 by sulphide of ammonium, as in antimonide of lead 

 (No. 55.) 



2. PROUSTITE. The light colored variety, when fused 

 in a current of hydrogen, loses all its sulphur and 

 arsenic ; but the complete expulsion of the latter can 

 scarcely be effected in a glass tube. The experiment 

 must be conducted in a small porcelain boat, placed 

 in a porcelain tube. After a certain time, the fused 

 substance suddenly swells up to a voluminous bladder- 

 like mass, from which the last portions of arsenic can 

 be but slowly expelled. 



The analysis may also be effected by dissolving the 

 red silver-ore in concentrated nitric acid. The diges- 

 tion is continued until the separated sulphur has a pure 

 yellow color; the solution is then diluted with hot 

 water, and filtered from the sulphur, the total quantity 

 of which may here be determined from the loss, unless 

 it be directly determined, as in the case of chalco- 

 pyrite (No. 30); the silver is precipitated by diluted 

 hydrochloric acid (see No. .1), the solution filtered off, 

 concentrated by evaporation, with addition of some 

 nitric acid or chlorate of 4)otassa, and the arsenic acid 

 precipitated by sulphate of magnesia. (See No. 51.) 



Or the very finely-powdered mineral may be fused 

 with 5 times its weight of a mixture of equal parts of 

 nitre and carbonate of soda in a platinum crucible, at 

 the bottom of which a layer of carbonate of soda has 

 been placed. The mass is afterwards dissolved out 

 with hot water, the silver filtered off', washed, ignited 

 and weighed. The solution is acidified with hydro- 

 chloric acid, mixed with ammonia, and the arsenic acid 

 precipitated by sulphate of magnesia. The amount 

 of sulphur is determined by loss, unless it be precipi- 

 tated from the original solution in the form of sulphate 

 of baryta, when it must be very carefully washed with 



