termed triple Prussiates. 543 
add also the account of the processes by which I have obtained 
it pure from the liquid in which it is formed. 
Processes by zvhich I have formed the Red Tinging Acid. 
A. The first is the one already mentioned, which consists 
in boiling, for a considerable length of time, three or four parts 
of Prussian blue in powder added at as many intervals, with 
one part of sulphuret of potash, which sulphuret by the action 
of the hot water upon it becomes an hydroguretted sulphuret. 
The products of this process are black sulphuret of iron, and 
a colourless neutral liquid containing a considerable quantity 
of the red tinging acid combined with potash, much sulphurous 
acid in union with sulphur and potash, forming a sulphuretted 
sulphite of potash, and some sulphate of potash. 
B. The second process is analogous to the preceding, it 
consists in decomposing prussiate of mercury by hydroguretted 
sulphuret of potash, this decomposition, owing to the solubi- 
lity of this prussiate, is instantaneous, while the former only 
takes place after a tedious ebullition ; the products of it do not 
differ in any respect from the former, with the exception, that 
instead of the black sulphuret of iron, there is formed the black 
sulphuret of mercury. 
C. The third process consists in heating to redness for some 
hours a mixture of animal charcoal and sulphuret of potash, 
and, when the mass is cold, lixiviating it with water. This 
process, which is by far the most economical of any, gives the 
same results as the former, with the exception of there being 
no metallic sulphurets, and that the liquid generally contains 
much undecomposed hydroguretted sulphuret of potash. 
4 A 2 
