547 
termed triple Prussiates. 
X. Experiments 27, 28, and 29. Sulphuretted sulphite of 
potash, prepared by adding sulphuret of potash to strong sul- 
phurous acid, was employed in the same manner, but like all 
the preceding substances, it was found to be incapable of 
forming an atom of tiie red tinging acid. 
The preceding series of experiments comprises all that I 
have made with the view of forming the red tinging acid ; they 
appear to prove, 
1st. 'That tins acid cannot be formed without sulphur. GH 
IKL. 
2d. That it cannot be formed v\ith sulphur, unless that sub- 
stance be in the state of hydroguretted sulphur. MNOPORS 
TUWX. 
3d. That it cannot be formed with hydroguretted sulphur, 
without the presence also of an alkali. V. 
It will be seen by reference to the successful experiments, that 
in them these essential conditions were fulfilled ; hence the indis- 
pensible agents in producing that peculiarchange on the Prussic 
acid which constitutes it the red tinging acid, may be considered 
as determined ; the nature of the change which they effect will 
be best understood, after relating my analytical experiments 
on the red tinging acid, previous to doing which, I have to de- 
scribe my process for obtaining the acid in a pure state from 
the liquid in which it is formed ; this process is the same in 
whatever mode the liquid has been obtained, it is the following : 
Let the clear liquor be brought to a decidedly acid state by 
the addition of sulphuric acid, then keep it for a short time at 
nearly the boiling point, when cold, throw into it a little native 
black oxide of manganese finely pulverised, wliich will turn it 
of a beautiful crimson colour, filter this crimson fluid, and add to 
