560 IRON. 



very soluble. The solution of the neutral salt is decomposed 

 near the boiling temperature, with the evolution of nitric oxide, 

 and the precipitation of a subnitrate of the peroxide in abun- 

 dance. Iron turnings dissolve in pure nitric acid, and form the 

 same salt, without the evolution of any gas, the water and acid 

 undergoing decomposition, so as to produce ammonia, while 

 they oxidate the iron. 



Protacetate of iron is obtained by dissolving the metal or 

 its sulphuret in acetic acid. It forms small green prisms, which 

 decompose very readily in the air. 



Tartrate of potash and iron is prepared by boiling bitar- 

 trate of potash with half its weight of iron turnings and a small 

 quantity of water. Hydrogen gas is evolved, and a white, 

 granular and sparingly soluble salt is formed, which blackens in 

 air from absorption of oxygen. It is used medicinally. The 

 iron of this salt is not precipitated either by hydrate or car- 

 bonate of potash. 



The titanate of iron occurs in masses of a metallic black, or 

 as black grains in volcanic sand. It crystallizes in the form of 

 peroxide of iron, (page 146), with which it is often mixed. Its 

 formula is FeO,TiO 2 . 



PERCOMPOUNDS OF IRON. 



Peroxide of iron, Ferric oxide, Fe 2 O 3 ; 978.4 or 78.36. 

 Occurs in great abundance in nature : 1 . As oligistic or specular 

 iron, in crystals derived from a rhomboid very near the cube, 

 which are of a brilliant metallic black and often iridescent. 

 Their powder is red; their density from 5.01 to 5.22. This 

 forms the celebrated Elba ore. 2. As red hematite, in fibrous, 

 mamillated, or kidney-shaped masses, of a dull red and very hard, 

 of which the density is from 4.8 to 5.0. This mineral is cut, 

 and forms the burnishers of blood-stone. 3. Also in combination 

 with water, as brown hematite, which is much more abundantly 

 diffused than the anhydrous peroxide, the granular variety 

 supplying, according to M. Berthier, more than three-fourths of 

 the iron furnaces in France. Its density is 3.922, its powder 

 brown, with a shade of yellow, and it dissolves readily in acids, 

 which the anhydrous peroxide does not. From analyses of 

 Dr. Thomson and M. Berthier, this mineral occurs with 1 eq. 

 of water, or HO, Fe 2 O 3 , analogous to the magnetic oxide of 



