COPPER, SILVER, AND GOLD 425 



to be an hydroxide, AgHO, t.e. AgN0 3 + KHO = KNO 3 + AgHO, 

 and the formation of the anhydrous oxide, 2AgHO = Ag 2 O + H 2 O, 

 may be compared with the formation of the anhydrous cupric oxide by 

 the action of potassium hydroxide on hot cupric solutions. Silver 

 hydroxide decomposes into water and silver oxide, even at low 

 .temperatures ; at least, the hydroxide no longer exists at 60, bub 

 'forms the anhydrous oxide, Ag 2 O. 19tri Silver oxide is almost 

 .insoluble in water ; but, nevertheless, it is undoubtedly a rather 

 powerful basic oxide, because it displaces the oxides of many metals 

 from their soluble salts, and saturates such acids as nitric acid, 

 forming with them neutral salts, which do not act on litmus paper. 20 

 Undoubtedly water dissolves a small quantity of silver oxide, 

 which explains the possibility of its action on solutions of salts for 

 example, on solutions of cupric salts. Water in which silver oxide 

 is shaken up has a distinctly alkaline reaction. The oxide is dis- 

 tinguished by its great instability when heated, so that it loses all its 

 oxygen when slightly heated. Hydrogen reduces it at about 80. 20 bis 

 The feebleness of the affinity of silver for oxygen is shown by the fact 

 that silver oxide decomposes under the action of light, so that it must be 

 kept in opaque vessels. The silver salts are colourless and decompose 

 when heated, leaving metallic silver if the elements of the acid are 

 volatile. 20 tri They have a peculiar metallic taste, and are exceedingly 

 poisonous ; the majority of them are acted on by light, especially in 

 the presence of organic substances, which are then oxidised. The 

 alkaline carbonates give a white precipitate of silver carbonate, 

 A.g 2 C0 3 , which is insoluble in water, but soluble in ammonia and 

 ammonium carbonate. Aqueous ammonia, added to a solution of a 

 normal silver salt, first acts like potassium hydroxide, but the precipitate 

 dissolves in an excess of the reagent, like the precipitate of cupric 



19 trl According to Carey Lea, however, oxide of silve? still retains water even at 100, 

 and only parts with it together with the oxygen. Oxide of silver is used for colouring 

 glass yellow. 



20 The reaction of Pb(OH) 2 upon AgHO in the presence of NaHO leads to the 

 formation of a compound of both oxides, PbOrtAg 3 O,' from which the oxide of lead 

 cannot be removed by alkalies (Wbhler, Leton). t Wb'hler, Welch, and others obtained 

 crystalline double salts, E s AgX 3 , by the action of strong solutions of EX of the halogen 

 salts of the alkaline metals upon AgX, where R = Cs, Eb, K. 



20t>i According to Miiller, ferric oxide is reduced by hydrogen" (see Chapter XXII., 

 Note 5) at 295 (into what ?), cupric oxide at 140, NL,O s t, 150 ; nickelous oxide, NiO, 

 js reduced to the suboxide, Ni^O, at 195, and to nickel at 270 ; zinc oxide requires so 

 high a temperature for its reduction that the glass tube ia which Miiller conducted the 

 experiment did not stand the heat ; antimony oxide requires a temperature of 215 for 

 its reduction ; yellow mercuric oxide is reduced at 180 and the red oxide at 230 ; silver 

 oxide at 85, and. platinum oxide even at the ordinary temperature. 



20 tH A silica compound, Ag 2 OSiO 2 is obtained by fusing AgNO 5 with eilica; this salt 

 is able to decompose with the evolution of oxvgen, leaving Ag + SiO a . 



