54® PoRRETT on the nature of the Salts 
and its effects on many of the metallic solutions. Since the 
experiments were performed which I then communicated, I 
have made several others which have added considerably to 
my knowledge of the nature and properties of this peculiar 
acid, and proved to me that my first opinion of its nature was 
incorrect. I shall endeavour in this paper to give as concise 
an account of these experiments as I am able, consistently with 
making myself understood, notwithstanding which I fear that 
from their number it will not be in my power to compress 
them within moderate limits ; in attempting this, however, I 
shall arrange them under the following heads: 
ist. Experiments on this acid of a synthetical nature, 
sdly. Experiments on the same of an analytical nature. 
5dly. Experiments on the salts formed by this acid. 
Before I detail the experiments of the first and second class 
which relate to the nature of this acid, I beg to observe that 
in describing them I shall designate this acid provisionally by 
the name of the red tinging acid, as neither the name of Prus- 
sous add, which I first gave to it, nor that of sulphuretted 
chyazic acid, which I now adopt, could in this place be used 
with propriety, as they each imply different compositions of 
this acid, the true nature of w’hich, until these experiments are 
related, must be presumed to be doubtful. 
Synthetical Experiments on the Red Tinging Acid, 
Under this head I shall include not only the different pro- 
cesses by which I have actually formed this acid, but those 
also by which I have attempted to form it without success, as 
both kinds of experiments throw light upon its nature ; I shall 
