440 Professor Berzelius on [June, 



succeeded. The water and the hydrocyanate are always disen- 

 gaged together, and the salt becomes green. Even when after 

 being highly dried, it gave a residuum by combustion of 28-5 per 

 cent, of oxide of iron, it still yielded water by distillation ; so 

 that in drying it, I only commenced its decomposition, which is 

 facilitated by the great tension of hydrocyanate of ammonia, and 

 by the tendency of the hydrocyanate of iron to form prussian 

 blue. 



IV. Frussian Blue, 



I prepared this substance by dropping a solution of cyanuret 

 of potassium and iron into one of muriate of iron, to which I had 

 previously added excess of acid. I washed the precipitate tho- 

 roughly and dried it. Prussian blue retains hygrometric moisture 

 so strongly, that sulphuric acid in vacuo does not detach it ; and 

 I have no doubt but that this salt when dried would possess the 

 property of causing water to freeze in vacuo quite as well as 

 sulphuric acid and some other substances. 



1 put some prussian blue into a cylindrical glass which I 

 placed in a small sand-bath. I placed the bulb of the thermo- 

 meter in the middle of the prussian blue, and heated the sandbath 

 gradually until the thermometer rose to 307° Fahr. The prussian 

 blue did not appear at all changed, and gave out no odour either 

 of hydrocyanic acid, or hydrocyanate of ammonia. I afterwards 

 placed the sand-bath thus heated in vacuo, with sulphuric acid, 

 and suffered it to cool. A portion of prussian blue thus dried 

 was weighed as quickly as possible, and then lighted at the 

 edge. It continued to burn by itself like amadou, giving a 

 vapour which condensed upon a funnel inverted over it : it was 

 carbonate of ammonia. One hundred parts of prussian blue left 

 a residuum of 60*14 parts of red oxide of iron, containing no 

 potash. 



It is well known that wJien a solution of protoxide of iron is 

 precipitated by prussiate of iron and potash, a white insoluble 

 compound is formed which contains potash, and which by 

 absorbing oxygen becomes blue. It is also well known that a 

 salt with base of protoxide, which absorbs oxygen without there 

 being at the same time an increase of acid, combines with an 

 excess of base. Prussian blue, therefore, which is prepared by 

 oxidrdion of the white precipitate, cannot be a neutral compound. 



I added a solution of neutral muriate of deutoxide of iron 

 to a solution of cyanuret of iron and potassium, and I left 

 the mixture exposed to the air until it became blue. The liquid 

 which still contained undecomposei 'yanuret, remained neutral; 

 this circumstance proves that no p jtash was set free, and conse- 

 quently that the blue compound did not contain a quantity of 

 acid proportional to the capacity of the base which had been 

 increased by oxidation. 



Prussian blue thus prepared has properties which it dees not 



