IRON. 147 



Ferric hydrate is a reddish-brown powder, frequently used as 

 an antidote in arsenic poisoning; for this purpose it is not used 

 in the dry state, but after having been freshly precipitated 

 and washed, it is mixed with water, and this mixture used. 

 Recently precipitated and consequently highly divided ferric 

 hydrate combines more readily with arsenious acid than the 

 hydrate which has been kept some time, or which has been 

 dried, and thereby assumed a more dense condition. 



Hydrated oxide of iron with magnesia, U. S. P., is a mixture 

 made by adding magnesia to a solution of ferric sulphate, when 

 magnesium sulphate and ferric hydrate are formed ; the two 

 substances are not separated from each other, the mixture being 

 intended for immediate administration as an antidote in cases 

 of arsenic poisoning. 



Ferrous-ferric oxide, FeO.Fe 2 3 (Magnetic oxide}. This com- 

 pound, which shows strong magnetic properties, has been men- 

 tioned above as one of the iron ores. It has a black color, and 

 is produced in the hydrated state by the addition of ammonium 

 hydrate to a mixture of solutions of ferrous and ferric salts. 



Trioxide of iron, Fe0 3 . Not known in a separate state, but in 

 combination with alkalies. In these compounds, called ferrates, 

 Fe0 3 acts as an acid oxide, analogous to chromic oxide, Cr0 3 , in 

 chromates. 



Ferrous chloride, FeCLj (Protochloride of iron), is obtained as a 

 pale green solution by dissolving iron in hydrochloric acid : 



Fe + 2HC1 = FeCl 2 + 2H. 



By evaporation of the solution, the dry salt may be obtained. 

 The solution and salt absorb oxygen very readily: 



3'FeCl 2 + O = FeO + Fe 2 Cl 6 . 

 Ferric chloride, ferrous, and afterwards ferric oxide, are formed. 



Ferric chloride, Ferri chloridum, Fe 2 Cl 6 .12H 2 == 540.2 (Chloride, 

 sesquichloride, or perchloride of iron), is obtained by adding to the 

 solution of ferrous chloride (obtained as mentioned above) 

 hydrochloric and nitric acids in sufficient quantities, and applying 



