44:4 M. Carey Lea — Notes on Silver. 



Art. LVL — Notes on Silver ; by M. Carey Lea. 



Action of Ammonia. — Aqueous ammonia is supposed to be 

 without action on normal silver but this is not so : under favor- 

 able conditions, silver is gradually taken up by this solvent. 



The first experiments were made with silver reduced from 

 the nitrate by the action of sodium hydroxide and milk sugar. 

 The silver was very carefully purified from any possible trace 

 of oxide. Placed in contact with ammonia for a few hours, 

 silver was taken up. Its presence could be recognized either 

 by ammonium sulphide or by adding a drop or two of hydro- 

 chloric acid and then supersaturating with dilute sulphuric acid ; 

 a dense cloud of silver chloride forms and this result can be 

 obtained any number of times in succession by acting with 

 ammonia on the same portion of silver. 



A similar reaction was obtained with silver reduced from 

 chloride by cadmium and hydrochloric acid removing afterwards 

 all traces of cadmium. Silver reduced in this way is liable to 

 contain traces of chloride. These were removed by covering 

 the silver with strong ammonia, letting it stand over night and 

 thoroughly washing out. This was repeated five times. From 

 this silver, ammonia by twenty-four hours contact always took 

 up enough to give a dense white cloud when treated as above. 



Portions of solutions obtained in the last mentioned manner 

 were evaporated to dryness over the water bath and left brown- 

 ish black films. These were non-explosive and therefore did 

 not consist of silveramine : they yielded a large proportion of 

 silver to acetic acid, leaving behind a little metallic silver. 

 The ammonia therefore, does not dissolve the silver as metal 

 but as oxide. The presence of a little metallic silver in the 

 residue left by evaporation was probably due to slight traces of 

 oxiclable organic matter contained in the ammonia. This opin- 

 ion was confirmed by the fact that the solution when heated 

 acquired a transparent red color. 



It appears therefore that in the presence of ammonia, silver 

 has a tendency to oxidize, for when the silver was placed in a 

 vial with an air-tight fitting stopper, filling it about half full, 

 and was then completely filled with liquid ammonia and tightly 

 closed, it was found that in twenty-four hours a mere trace of 

 silver was taken up. On the other hand when the silver was 

 placed in a flat basin and merely moistened with ammonia 

 more silver was taken up in five minutes than in the preceding 

 case in twenty four hours. 



This action of ammonia in promoting oxidation recalls its 

 behavior with cobaltous salts and with copper. It is probably 



