172 METALS AND THEIR COMBINATIONS. 



ammonium sulphate, Fern et ammonii sulphas, (NH 4 ) 2 SO 4 .Fe 2 (SO 4 ) 3 . 

 24H 2 O (iron alum or ammonio-ferric alum), which is made by mixing 

 solution of ferric sulphate with ammonium sulphate and crystallizing. 

 The salt has a pale violet color and is readily soluble in water. 



Solution of ferric subsulphate, Liquor ferri subsulphatis 

 (Monsel's solution). This is a solution similar to the preceding, but 

 contains less sulphuric acid, and is, therefore, looked upon as a basic 

 ferric sulphate, of the doubtful composition 5[Fe 2 (SO 4 ) 3 ].Fe 2 (OH) 6 . 



Ferric nitrate, Fe 2 (NO 3 ) 6 . A 6 per cent, solution of this salt is 

 official, under the name Solution of ferric nitrate. Liquor ferri nitratis, 

 U. S. P., and is made by dissolving ferric hydroxide in nitric acid : 

 Fe 2 (OH) 6 + 6HN0 3 = 6H 2 O + Fe 2 (NO 3 ) 6 . 



It is an amber-colored, or reddish, acid liquid. 



Ferrous carbonate, FeCO 3 . Occurs in nature ; may be obtained 

 by mixing solutions of ferrous sulphate and sodium carbonate or 

 bicarbonate : 



FeSO 4 + 2NaHCO 3 = Na 2 SO 4 + FeCO 3 



The precipitate is first nearly white, but soon assumes a gray color 

 from oxidation. The saecharated carbonate of iron, U. S. P., is made 

 by mixing the washed precipitate with sugar, and drying. The 

 sugar prevents, to some extent, rapid oxidation. The preparation 

 contains 15 per cent, of ferrous carbonate. 



Ferric carbonate does not exist, the affinity between the feeble ferric 

 oxide and the weak carbonic acid not being sufficient to unite them 

 chemically. 



Ferrous phosphate, Fe 3 (PO 4 ) 2 . When sodium phosphate is 

 added to solution of ferrous sulphate, a precipitate of the composi- 

 tion FeHPO 4 is formed : 



Na 2 HPO 4 -f FeSO 4 = FeHPO 4 + Na^O,. 



If, however, sodium acetate is added, a precipitate of the composi- 

 tion Fe 3 (PO 4 ) 2 is formed : 



3FeSO 4 + 2Na 2 HPO 4 = Fe 3 (PO 4 ) 2 + 2Na 2 SO 4 + H 2 SO 4 . 



The sulphuric acid liberated, as shown in this formula, decomposes 

 the sodium acetate, forming sodium sulphate and free acetic acid. 

 Ferrous phosphate is a slate-colored powder, absorbing oxygen 

 readily, becoming darker in color. 



