424 PEINCIPLES OF CHEMISTRY 



but there is no action at the ordinary temperature, even in the presence 

 of air. Among the various salts, sodium chloride (in the presence of 

 moisture, air, and carbonic acid) and potassium cyanide (in the presence 

 of air) act on silver more decidedly than any others, converting it respec- 

 tively into silver chloride and a double cyanide. 



Although silver does not directly combine with oxygen, still three 

 different grades of combination with oxygen may be obtained indi- 

 rectly from the salts of silver. They are all, however, unstable, and 

 decompose into oxygen and metallic silver when ignited. These three 

 oxides of silver have the following composition : silver suboxide, 

 Ag 4 O, 19 corresponding with the (little investigated) suboxides of the 

 alkali metals ; silver oxide, Ag 2 O, corresponding with the oxides of the 

 alkali metals and the ordinary salts of silver, AgX ; and silver peroxide, 

 AgO, 19 bis or, judging from Berthelot's researches, Ag 2 O 3 . Silver oxide 

 is obtained as a brown precipitate (which when dried does not contain 

 water) by adding potassium hydroxide to a solution of a silver salt 

 for example, of silver nitrate. The precipitate formed seems, however, 



19 Silver suboxide (Ag 4 0) or argentous oxide is obtained from argentic citrate by 

 heating it to 100 in a stream of hydrogen. Water and argentous citrate are then 

 formed, and the latter, although but slightly soluble in water, ' gives a reddish' 

 brown solution of colloid silver (Note 18), and: when boiled this solution becomes 

 colourless and deposits metallic silver, the argentic salt being again formed. Wb'hler, 

 who discovered this oxide, obtained it as a black precipitate by adding potassium 

 hydroxide to the above solution of argentous citrate. With hydrochloric acid the 

 suboxide gives a brown compound, Ag 2 Cl. Since the discovery of soluble silver the 

 above data cannot b Regarded as perfectly trustworthy ; it is probable that A mixture of 

 Ag 2 *and Ag 2 was. being dealt with, so that the actual existence of Ag 4 O is' now 

 doubtful, but there can be no doubt as to. the formation of a subchloride, Ag 2 Cl (see 

 Note 25), corresponding to the suboxide. The same compound is obtained by the action 

 of light on the higher chloride. Other, acids do .not combine with silver suboxide, but 

 convert it into an argentic salt and metallic silver. In this respect cuprous oxide 

 presents a certain .resemblance to these suboxides. But copper forms a suboxide of 

 the composition Cu 4 O, which is obtained by the action of an alkaline solution of 

 etannous oxide on cupric hydroxide, and is decomposed by acids into cupric salts and 

 metallic copper. The problems offered by the suboxides, as well as by the peroxides, 

 cannot be considered as fully solved. 



19 bls Silver peroxide, AgO or Ag 2 O 3 , is obtained by the decomposition of a dilute 

 (10 p.c.) solution of silver nitrate by the action of a galvanic current (Hitter). On the 

 positive pole, where oxygen is usually evolved in the decomposition of salts, brittle grey 

 needles with a metallic lustre, which occasionally attain a somewhat considerable size, 

 are then formed. They are insoluble in water, and decompose with the evolution of 

 oxygen when they are dried.. and heated, especially up to 160, and, like lead dioxide, 

 barium peroxide, &c., their action is strongly oxidising. When treated with acids, oxygen 

 is evolved and a salt of the oxide formed. Silver peroxide absorbs sulphurous anhydride 

 and forms silver sulphate. Hydrochloric acid evolves chlorine ; ammonia reduces the 

 silver, and is itself oxidised, forming water and gaseous nitrogen. Analyses of the above- 

 mentioned crystals show that they contain silver nitrate, peroxide, and water. According 

 to Fisher, they have the composition 4AgO,AgN05,H 8 O, and, according to Bertbelot, 



