562 IRON. 



Iron is most conveniently distinguished by tests, or precipi- 

 tated for its quantitative estimation, when in the state of per- 

 oxide. The solution of a proto-salt is usually peroxidised by 

 transmitting a current of chlorine through it, or by adding to it, 

 at the boiling point, nitric acid, in small quantities, so long as 

 effervescence is occasioned from the escape of nitric oxide. 

 Alkalies and alkaline carbonates precipitate the peroxide in the 

 state of hydrate. Sulphuretted hydrogen converts a persalt of 

 iron into a protosalt, with precipitation of sulphur. The ferro- 

 cyanide of potassium throws down prussian blue, but the ferri- 

 cyanide has no effect upon a persalt of iron. The sulphocyanide 

 of potassium produces a deep wine-red solution with a persalt 

 of iron, which becomes perfectly colourless when considerably 

 diluted with water, provided the salt of iron is not in great 

 excess. Infusion of nut-galls produces a bluish black precipitate 

 the basis of common writing ink. 



Black or magnetic oxide of iron, Fe O, Fe 2 O 3 , called also 

 the ferroso-ferric oxide, an important ore of iron, is a compound 

 of the two oxides. It crystallizes in the regular octohedron. 

 In this compound, the peroxide of iron may be replaced by 

 alumina and by oxide of chromium, and the protoxide of iron 

 by oxide of zinc, magnesia, and protoxide of manganese, without 

 change of form. It was produced artificially, by Liebig and 

 Wohler, by mixing the dry protochloride of iron with an excess 

 of carbonate of soda, calcining the mixture in a crucible, and 

 treating the mass with water. The double oxide remains as a 

 black powder, which may be washed and dried without its 

 oxidating farther. The same chemists, by dissolving the black 

 oxide in hydrochloric acid, and precipitating by ammonia, 

 obtained a hydrate of the double oxide. It was attracted by a 

 magnet, even when a flocculent precipitate suspended in water. 

 When ignited and anhydrous, this double oxide is much more 

 magnetic than iron itself. 



Sesguisulphuret of iron, or Ferric sulphuret, Fe 2 S 3 , cor- 

 responding with the peroxide, may be prepared by pouring, 

 drop by drop, a solution of a persalt of iron, into a solution of 

 an alkaline sulphuret, the last being preserved in excess. At a 

 low red heat, it loses 2-9ths of its sulphur and becomes mag- 

 netic pyrites. The common yellow iron pyrites is the bisulphuret 

 of iron. It crystallizes in the cube or other forms of the regular 

 system, its density is 4.981. It may be formed artificially by 



