564 IRON. 



a solution of the yellow prussiate of potash, charged with an 

 excess of chlorine, is heated or exposed to air. The precipitate 

 should be boiled with eight or ten times its weight of concen- 

 trated hydrochloric acid, and well washed. Its formula is, 

 FeCy, Fe 2 Cy 3 + 4HO* 



Sesquiferrocyanide of iron, Prussian blue, Fe 4 , 3(Cy 3 Fe). 

 This remarkable substance precipitates whenever the yellow 

 prussiate of potash is added to a persalt of iron. For the 

 preparation of prussian blue in quantity, Liebig recommends 

 the following process of Hochsteller. Six parts of green vitriol 

 and six parts of yellow prussiate of potash to be dissolved, each 

 by itself, in fifteen parts of water, the solutions mixed, and an 

 addition then made to them of one part of oil of vitriol, and 

 twenty four parts of strong hydrochloric acid. After some 

 hours, a clear solution of one part of chloride of lime in eighty 

 parts of water is gradually added, by small portions, observing 

 the precaution to stop as soon as an effervescence is observed, 

 from the disengagement of chlorine. After being allowed to 

 subside for several hours, the precipitate is washed and dried at 

 the usual temperature, or by artificial heat. It is said that the 

 finest colour is obtained by heating the precipitate with dilute 

 nitric acid, till it acquires a deep blue colour, instead of oxidis- 

 ing by chlorine. 



Prussian blue, dried at the temperature of the air, is a light 

 porous body, of a rich velvety blue colour ; dried at a higher 

 temperature, it is more compact, and exhibits in mass a coppery 

 lustre. It is tasteless, and not poisonous. Alkalies decompose 

 it, precipitating peroxide of iron and reproducing an alkaline 

 ferrocyanide. This renders prussian blue of little value in 

 dyeing, as it is injured by washing with soap. Red oxide of 

 mercury, boiled with prussian blue, affords the soluble cyanide 

 of mercury, with an insoluble mixture of oxide and cyanide of 

 iron. It is destroyed by fuming nitric acid, but combines with 

 oil of vitriol, forming a white pasty mass, which is decomposed 

 by water. 



In the formula above, prussian blue is represented as con- 

 sisting of 4 eq. of iron and 3 eq. of the bibasic salt-radical, 

 ferrocyanogen, and, therefore, named a sesquiferrocyanide. It 

 contains oxygen and hydrogen, besides, which cannot be sepa- 



* Pelouze, An. cle Ch. et cle Ph. t. 69, p. 40. 



