termed triple Pnis slates. 541 
The succinates and benzoates which have been proposed as 
superior tests for determining the quantity of iron, to the fer- 
ruretted chyazates, I consider to be in general very inferior to 
them, because they do not precipitate the iron, when it is in 
the state of protoxide, which the latter do, and because they 
precipitate alumine more effectually than those salts. 
On sulphuretted Chyazic Acid. 
I discovered this acid in the latter part of the year 1808, 
whilst engaged in an experiment the object of which was to 
form prussiate of potash by the mutual action of Prussian blue 
and sulphuret of potash when boiled together; I found after 
this boiling had been continued for a considerable time with 
fresh additions of Prussian blue, until the alkaline liquid was 
completely neutralized, that instead of prussiate of potash 
which I had expected to obtain, a new principle had been 
formed which had properties totally different from the Prussic 
acid, or from any other known chemical substance. I made 
experiments in order to separate this principle from the vari- 
ous products which were mingled with it in the liquid which 
I obtained, and having succeeded in this, I found that in its 
pure state it had acid properties, and was capable of being 
converted by oxidizing agents into Prussic acid ; this circum- 
stance considered in conjunction with its being formed by a 
deoxidating process on a salt of iron containing the Prussic 
acid, led me to conclude, that this new acid differed from the 
Prussic acid only in containing less oxygen, I therefore named 
it Prussous Acid, and in a paper which I presented to the 
Society of Arts in April 1809, detailed the circumstances of 
its formation, the mode of obtaining it free from foreign bodies, 
MDCCCXIV. 4 A 
