termed triple Prussiates, 53 1 
combinations, when it can form with their bases compounds 
that are insoluble in acids. 
The decomposition of the abovementioned peculiar acid by 
heat, shews the reason why the acid of the triple prussiates 
can never be obtained from them by distilling these salts with 
a stronger acid, and why in these cases. Prussic acid and triple 
prussiate of iron are always obtained. 
By proving that the oxide of iron contained in the triple 
prussiates is an elementary part of an acid sui generis, the 
several anomalies mentioned in the beginning of this Paper 
are easily explained, for instance, its occasioning the simple 
prussiates to pass from an alkaline to a neutral state, is owing 
to its constituting with the other elements present, a new acid 
liaving much stronger acid properties than the Prussic. Its 
not being affected by the usual tests for iron is owing to its 
existing as an element of an acid, in which state it is no more 
to be expected that it should be discovered by the ordinary 
reagents, than that the sulphur in sulphuric acid should blacken 
metallic solutions. Finally, its accompanying the elements of 
the Prussic acid in all cases of transfer from one base to an- 
other, is owing to its forming with these elements the acid of 
the triple prussiates, which acid, when transferred by stronger 
affinities, carries with it of course all its component parts. I 
have discovered that besides the black oxide of iron there are 
other substances which are capable of forming, with the ele- 
ments of Prussic acid, peculiar acids having properties widely 
different from each other. 
Sulphur is one of these substances. 
Several of the metallic oxides, I have reason to think, are 
