312 
FERROCYANIDE OF POTASSIUM, ETC. 
iron, (as sulphate, nitrate, or chloride,) is not dissolved by 
tartaric acid only, and is not at all modified ; but on adding 
ammonia afterwards, the blue becomes white, presenting 
the intermediate phases of coloration according to the quan- 
tity of ammonia added. Thus it becomes violet-purple, 
amethyst, rose, pale rose, and then white. This white pre- 
cipitate becomes blue by the addition of a new quantity of 
tartaric acid, and returns to while by ammonia. Exposed 
to the air and under water, it remains white, but becomes 
again blue by drying. 
The interesting point of this reaction is, that it is alto- 
gether according as you throw on the prussian blue, a ready 
made solution of tartrate of ammonia, or tartaric acid, and 
then ammonia afterwards. In the first case, the prussian 
blue is dissolved, and the solution has a magnificent violet 
colour ; in the second, the precipitated prussian blue does 
not dissolve, and the blue becomes immediately white. 
The vegetable salt also modifies the prussian blue, but it 
does not totally change the colour even when employed in 
excess. 
The property enjoyed by tartrate of ammonia of dissolving 
prussian blue, was first announced by M. Monthiers. This 
fact I had already personally ascertained, and of which I 
had taken a note, proposing to myself to examine it at my 
leisure. — Journ. de Pharm. et de Chim. 
