566 IRON. 



formed ceases to redissolve, and the solution is evaporated in 

 vacuo. 



Berzelius designates as the f err o so-ferric sulphate a combina- 

 tion of the proto and persulphates of iron, Fe O, SO 3 + 

 Fe 2 O 3 , 3SO 3 . It is the salt produced when a solution of the 

 neutral protosulphate of iron is exposed to the air, till no more 

 ochre is precipitated. The solution, which is yellowish red, 

 does not crystallize, but gives the black oxide of iron when 

 precipitated by an alkali. A salt of the same constituents, but 

 in different proportions, forms large stalactites, composed of 

 little transparent crystals, in the copper mine of Fahlun. It is 

 represented by 3Fe O, 2SO 3 -f3(Fe 2 O 3 , 2SO 3 ) + 36HO, (Ber- 

 zelius.) 



Pernitrate of iron. By dissolving iron in nitric acid, without 

 heat, as in Schoenbein's experiments, (page 553), a salt is ob- 

 tained in large, transparent, and colourless crystals. From 

 more than one analysis, M. Pelouze found the constituents pf 

 this salt to be in the proportion of 2Fe 2 O 3 -f 3NO 5 + UHO. 

 Its solution is decomposed by heat, and the peroxide of iron 

 precipitates. 



Peroxalate of iron is very soluble and does not crystallize. 

 It forms a double salt with the oxalate of potash, of a rich 

 green colour, of which the formula is 3(KO,C 2 O 3 ) -f Fe 2 O 3 ,3C 2 O 3 

 + 6HO. The crystals effloresce in dry air. In this double 

 salt, the peroxide of iron may be replaced by alumina and oxide 

 of chromium (page 519.) This salt is formed by dissolving the 

 hydrated peroxide of iron to saturation, in binoxalate of potash, 

 (salt of sorrel,) and crystallizes readily from a concentrated 

 solution. The circumstance of its being the salt of peroxide of 

 iron most easily obtained and preserved in a dry state, should 

 recommend it as a pharmaceutical preparation. 



The benzoate and succinate of peroxide of iron are insoluble 

 precipitates. Hence the benzoate and succinate of ammonia 

 are employed to separate iron from manganese. As both these 

 precipitates are dissolved by acids, the iron solution should be 

 made asjneutral as possible. The formula of the succinate is, 

 Fe 2 3 ,S. 



