228 



reducing action of metallic sulphides and ai-senides upon salts of gold mani- 

 fested, it became of some intei'est to ascertain whether or not any other 

 metallic salts were capable of being reduced by these, or any of these 

 substances. 



This part of the subject I have only slightly investigated, but enough has 

 been discovered to show that silver and one or more of the metals of the 

 platinum series, are reduced from their soluble salts by these substances 

 generally. 



Thus, silver is reduced from either its nitrate or acetate very readily by 

 galena, copper pyrites, and the inferior sulphides of iron and copper; from 

 ammoniacal solutions, however, it does not precipitate on any of these 

 sulphides, not even when heated with them, except upon sub-sulphide of 

 copper ; as reduced by galena, it selects some angular jjart of it to deposit on, and 

 sometimes strikes off from this in beautiful arborescent forms, and minutely 

 crystalline filaments, exactly like those which the metal generally assumes in 

 its native state. 



Cubic iron pyrites, also stibnite, has little or no effect upon silver salts, not 

 even when heated with them ; arsenide of silver has, however, a feeble effect. 



The metal platinum is very slowly removed from its bichloride solution by 

 galena and grey cojoper ore ; also by iron pyrites, but still more slowly. 

 These were the only sulphides tiied. 



Mercury does not appear to be reduced to the metallic state by any of the 

 sulphides enumerated, from its bichloride solution, but most of them reduce it 

 to the sub-chloride, — sulphide of gold even, thus affects this mercurial salt, the 

 sulphur being oxydized and the gold set free. 



Neither the sulphate nor the acetate of copper are affected by these 

 sulphides, but per-chloride of iron is reduced to the proto-chloride by galena 

 and grey copper ore. 



Before I proceed to the next part of the subject, I will state here the 

 results I obtained when other gold solutions were administered to these 

 sulphides ; the one hitherto employed in the experiments described being, as 

 will be remembered, a chloride. 



When, in the place of this salt, I applied the oxide of gold in solution of 

 either potash, bicarbonate of soda, or silicate of potash, the effects were 

 always the same ; at least they were so with galena, sulphide of copper, or 

 proto-sulphide of iron. 



Ammoniacal solutions of gold, however, required their temperature raised 

 to 200° F., in order to give a decided gold deposit on these sulphides; 

 while in the case of the stoljyJiide of gold, dissolved in either bicarbonate or 

 soda, silicate of potash or ammonia, no reduction of the metal occurred by 

 contact with any of the sulphides enumerated, either at common temperatures 

 or at that of the boiling point of these several solutions ; nor yet was any 



