544 PoRRETT on the nature of the Salts 
D. The fourth process is only a variation of the third, by 
substituting for the sulphuret of potash, the sulphate of that 
alkali, which sulphate is converted to sulphuret during the 
process by part of the animal coal ; 1 performed this process 
but once, but it did not appear to me to give so large a quan- 
tity of the red tinging acid as the last. 
E. The fifth process consists in forming the simple alkaline 
prussiate of potash by passing Prussic acid gas through a so- 
lution of that alkali, and afterwards boiling this liquid alkaline 
prussiate with a little sulphur, the whole of the Prussic acid 
in this salt is thus changed into red tinging acid. 
F. The sixth process is very analogous to the last, it con- 
sists in adding to the simple prussiate of ammonia, hydrogu- 
retted sulphuret of potash, by which the simple prussiate of 
ammonia is immediately changed into the compound of am- 
monia with the red tinging acid. The liquid after the process 
always contains sulphuretted hydrogen, even when the hy- 
droguretted sulphuret has been added in a quantity insufficient 
to convert the whole of the Prussic acid into red tinging 
acid. 
These are the various processes by which I have formed 
the red tinging acid, those by which I could 7iot form it are 
now to be mentioned. 
G. B.xperiment i. Ammoniacal gas was passed through a 
red hot earthen tube containing charcoal, by this process as 
is well known Prussic acid is abundantly formed, but my ob- 
ject in performing it, was to ascertain whether any of the red 
tinging acid was at the same time produced ; not the slightest 
trace of it, however, could be detected in any of the products. 
