IRON. 171 



Experiment 27. Cover some fine iron wire with water, heat gently, and add 

 iodine in fragments as long as the red color of iodine disappears. Notice that 

 the iron is dissolved gradually, the result of the reaction being the formation 

 of a pale-green solution of ferrous iodide. 



Ferrous bromide, PeBr 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 combine. It 

 is used chiefly for liberating hydrogen sulphide, 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, FeSO 4 .7H 2 O = 277.9 (Sul- 

 phate of iron, G-reen vitriol, Copperas). Obtained by dissolving iron 

 in dilute sulphuric acid, evaporating, and crystallizing : 



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



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

 try, and by heap-roasting of the native iron sulphide : 

 FeS 2 + 6O = FeS0 4 + SO 2 . 



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 about 

 4 molecules of water by heating to 100 C. (212 F.); the granu- 

 lated (precipitated) ferrous sulphate is made by pouring a strong aque- 

 ous solution of ferrous sulphate, slightly acidulated with sulphuric 

 acid, into alcohol, when ferrous sulphate separates as a crystalline 

 powder, which is washed and dried. 



Ferric sulphate, Fe 2 (SO 4 ) 3 . The solution of this salt, Liquor 

 Jerri tersulphatis, Solution of ferric sulphate, U. S. P., is made by 

 adding sulphuric and nitric acids to a solution of ferrous sulphate 

 and heating : 



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



The action of nitric acid is similar to that described above under 

 ferric chloride. The hydrogen of the sulphuric acid is oxidized, and 

 the radical SO 4 unites with the ferrous sulphate, nitrogen dioxide 

 being liberated. 



Solution of ferric sulphate is used in the preparation of Ferric 



