M. Carey Lea — Notes on Silver. 446 



the only case in which silver is oxidized (at ordinary tempera- 

 tures) by atmospheric oxygen. 



Action of Dilute Sulphuric Acid. — It is generally held that 

 silver is insoluble in cold dilute sulphuric acid. Almost any 

 form of silver, providing it is finely divided, is slightly soluble 

 in sulphuric acid diluted with four or five times its bulk of 

 water. With more dilute acid different varieties of silver act 

 very differently. The most easily attacked is that which is 

 obtained by reducing the oxide with alkaline hydroxide and 

 milk sugar ; from this a distinct trace is dissolved by sulphuric 

 acid diluted with 100 times its bulk of water. From silver 

 reduced from the chloride by cadmium this very dilute acid 

 takes up nothing. 



Nitric acid, sp. gr. 1*40, diluted to ten volumes and allowed 

 to stand for an hour with finely divided silver, took up an ex- 

 tremely faint trace. 



Hydrochloric acid, sp. gr. l - -20, was totally without action. 

 The silver after being well boiled with water to remove every 

 trace of acid, dissolves completely in nitric acid. 



Acetic acid has no action upon metallic silver. 



Various Reactions of Normal Silver. 



Normal metallic silver even in a state of very fine division 

 does not abstract the slightest trace of nitric acid from perfectly 

 neutral cupric nitrate obtained by acting on pure cupric sul- 

 phate with barium nitrate. After fifteen hours of contact not 

 a trace of silver had been dissolved. 



But silver easily reduces cupric chloride with formation of 

 purple photochloride. If the copper salt is present in slight 

 excess the silver is so thoroughly acted upon that nitric acid 

 does not extract a trace of it from the purple photochloride. 



Metallic mercury instantly reduces silver nitrate but metallic 

 silver takes chlorine from corrosive sublimate. The precipi- 

 tate contains calomel and blackens with ammonia. 



Silver in fine division slowly reduces a neutral solution of 

 potassium permanganate. 



Silver nitrate, as is well known, is reduced by ferrous sul- 

 phate, or ammonia ferrous sulphate, the iron at the same time 

 becoming peroxidized and the silver assuming the gray metallic 

 form. On the other hand silver powder rapidly reduces a neu- 

 tral solution of ferric sulphate. A solution of iron alum 

 readily dissolves metallic silver without the aid of heat;* in a 

 few seconds the solution strikes a blue color with potassium 



* The statement in the new Encyclopedic Ohimique that heat is required and 

 that the metal separates again on cooling (Tome iii, cahier 15, p. 248) appears to 

 be incorrect. 



