SILVER. 173 



Silver nitrate, Argenti nitras, AgN0 3 = 169.7 (Nitrate of silver}. 

 Pure silver is dissolved in nitric acid : 



3Ag + 4HNO 3 = NO + 2H 2 O -f 3AgNO 3 . 



The solution is evaporated to dry ness with the view of expel- 

 ling all free acid, the dry mass dissolved in hot water and 

 crystallized. "When fused and poured into suitable moulds it 

 yields the white cylindrical sticks which are usually known as 

 caustic, lunar caustic, or lapis inf emails. 



When fused with an equal weight of potassium nitrate and 

 formed into similar rods, it represents the diluted nitrate of silver 

 of the U. S. P. 



Silver nitrate forms colorless, transparent, tabular, rhombic 

 crystals, or, when fused, a white, hard substance; it is soluble 

 in less than ^ts own weight of water, the solution having a 

 neutral reaction. Exposed to the light, especially in the presence 

 of organic matter, silver nitrate blackens in consequence of de- 

 composition : when brought in contact with animal matter, it is 

 readily decomposed into free nitric acid and metallic silver, 

 which produces the characteristic black stain; it is this decom- 

 position, and the action of the free nitric acid, to which the 

 strongly caustic properties of silver nitrate are due. 



Nitrate of silver is used largely in photography, and also in 

 the manufacture of various kinds of indelible inks and hair- 

 dyes. 



Silver oxide, Argenti oxidum, Ag 2 = 231.4 (Oxide of silver). 

 Made by the addition of an alkaline hydrate to silver nitrate : 



2AgNO 3 + 2KHO = 2KNO 3 + H 2 O + Ag 2 O. 



A dark brown, almost black powder, but very sparingly 

 soluble in water, imparting to the solution a weak alkaline re- 

 action. It is a strong base, and easily decomposed into silver 

 and oxygen. 



Silver iodide, Argenti iodidum, Agl 234.3 (Iodide of silver). 

 Made by the addition of potassium iodide to silver nitrate : 



AgN0 3 -f KI = KN0 3 , + Agl. 



