IRON. 149 



As it is easily oxidized and decomposed by the action of the 

 air, an officinal preparation, the saccharated iodide of iron, U. S. P., 

 is made by adding about 80 parts of sugar of milk to 20 parts 

 of the ferrous iodide ; the sugar prevents, to some extent, rapid 

 oxidation. 



Ferrous bromide, FeBr 2 . Made analogously to ferrous iodide, 

 by the action of bromine on metallic iron. 



Ferrous sulphide, FeS. Easily obtained as a black, brittle mass, 

 by heating iron filings with sulphur, when the elements com- 

 bine. It is chiefly used for liberating hydrosulphuric acid, by 

 the addition of sulphuric acid. Iron combines with sulphur in 

 several proportions; some of these iron sulphides are found 

 in nature. 



Ferrous sulphate, Ferri sulphas, FeS0 4 .7H 2 =277.9 (Sulphate of 

 iron, Green vitriol, Copperas). Obtained by dissolving iron in 

 sulphuric acid, evaporating, and crystallizing : 



Fe + H 2 S0 4 = 2H + FeSO 4 . 



Also obtained as a by-product in some branches of chemical 

 industry, or by oxidation of the native sulphide of iron : 



FeS 2 + 40 = FeS0 4 + S. 



Ferrous sulphate crystallizes in large, bluish-green prisms; it 

 is soluble in water, insoluble in alcohol. Exposed to the air, 

 it loses water of crystallization, and absorbs oxygen. 



The dried ferrous sulphate, U. S. P., is made by expelling all 

 water by heat; the precipitated ferrous sulphate is made by pouring 

 a strong aqueous solution of ferrous sulphate, slightly acidulated 

 with sulphuric acid, into alcohol, when ferrous sulphate sep- 

 arates as a crystalline powder, which is washed and dried. 



Ferric sulphate, Fe 2 3S0 4 . The solution of this salt, Liquor ferri 

 tersidphatis, solution of tersulphate of iron, U. S. P., is made by 

 adding sulphuric and nitric acids to a solution of ferrous sul- 

 phate, and heating : 



6FeSO 4 + 3H,SO 4 + 2HNO 3 = 3(Fe 2 3SO 4 ) + 2NO -f- 4H 2 O. 



