428 PRINCIPLES OF CHEMISTRY 



decompose at an incipient red heat ; when cast into sticks it is usually 

 employed for cauterising. On further heating,. the fused salt undergoes 

 decomposition, first forming silver nitrite and then metallic .silver. 

 With ammonia, silver nitrate forms, on evaporation of the solution, 

 colourless crystals containing AgNO 3 ,2HN 3 (Marignac). In general 

 the salts of silver, like cuprous, cupric, zinc, &c. salts, are able to give 

 several compounds with ammonia j for example, silver nitrate in a dry 

 state absorbs three molecules (Rose). The ammonia is generally easily 

 expelled from these compounds by the action of heat. 



Nitrate of silver easily forms double salts like AgN0 3 2NaNO 3 and 

 AgNO 3 KNO 3 . Silver nitrate under the action of water and a halogen 

 gives nitric acid (see Vol. I. p* 280, formation of N 2 O 5 ), a halogen salt of 

 silver, and a silver salt of an oxygen acid of the halogen. Thus, for 

 example, a solution of chlorine in watery when mixed with a solution of 

 silver nitrate, gives silver chloride and chlorate. It is here evident that 

 the reaction of the silver nitrate is identical with the reaction of the 

 caustic alkalis, as the nitric acid is all set free and the silver oxide x>nly 

 reacts in exactly the same way in which aqueous potash acts on free 

 chlorine. Hence the reaction may be expressed in the following 

 manner : 6AgNO 3 + 3C1 2 + 3H 2 = SAgCl + AgC10 3 + 6NH0 3 . 



Silver nitrate, like the nitrates of the alkalis, does not contain any 

 water of crystallisation. Moreover the other salts of silver almost 

 always separate out without any water of crystallisation. The silver 

 salts are further characterised by the fact that they give neither 

 basic nor acid salts, owing to which the formation of silver salts 

 generally forms the means of determining the true composition of 

 acids thus, to any acid H n X there corresponds a salt Ag n X for 

 instance, Ag 3 P0 4 (Chapter XIX., Note 15). 



Silver gives insoluble and exceedingly stable compounds with the 

 halogens. They are obtained by double decomposition with great 

 facility whenever a silver salt comes in contact with halogen salts. 

 Solutions of nitrate, sulphate, and all other kindred salts of silver give 

 a precipitate of silver chloride or iodide in solutions of chlorides and 

 iodides and 6f the halogen acids, because the halogen salts of silver are 

 insoluble both in water 23 and in other acids. Silver chloride, AgCl, is 



25 Silver chloride is almost perfectly insoluble in water, but is somewhat- soluble i 

 water containing sodium chloride or hydrochloric acid, or other chlorides, and many salts, 

 in solution. Thus at 100, 100 parts of water saturated with sodium chloride dissolve 

 0'4 part of silver chloride. Bromide and iodide of silver are less soluble in this respect, 

 as also in regard to other solvents. It should be remarked that silver chloride dissolves 

 in solutions of ammonia, potassium cyanide, and of sodium thiosulphate, Na2S 2 O5. 

 Silver bromide is almost perfectly analogous to the chloride, but silver iodide is nearly 

 insoluble in a solution of ammonia. Silver ehloride even absorbs dry ammonia g% 



