434 M. Vauquelin’s Memoir on (J UNE, 
formed ; and that this last substance, instead of uniting exelu- 
sively with ammonia, combines likewise with the oxide of iron. 
There is also deposited a charry matter, and it is probable that 
cyanic acid is likewise formed ; but M. Vauquelin was not able 
to ascertain its presence. 
Cyanogen dissolved in water, when placed in contact with 
metallic iron, is decomposed as it would be in water alone. But 
in this case, the phenomena that take place are much more 
difficult of explanation. M. Vauquelin is led to believe that the 
iron decomposes the water, that it unites with the oxygen of that 
liquid ; while the nascent hydrogen combines with a portion of 
the cyanogen and converts it into hydrocyanic acid ; and these 
produce hydrocyanate of iron and ammonia. “ Yet, admitting 
the decomposition of water,” says M. Vauquelin, “ we must 
allow at the same time that the cyanogen is likewise decom- 
posed, as we find in the liquid carbonic acid and the peculiar 
acid, which could not have been formed out of the oxygen of 
the water. It is certain at least that metallic iron, as well as the 
oxide of that metal, accelerates, in a remarkable degree, the 
decomposition of the cyanogen, probably by acting on it as a~ 
weak alkali in proportion as it is oxidized.” 
Action of Hydrocyanic Acid on Iron. 
The importance of this paragraph induces us to copy literally 
the text of M. Vauquelin. 
“ Hydrocyanic acid diluted with water, when placed in contact 
with iron in a glass vessel standing over mercury, quickly pro- 
duced prussian blue, while at the same time hydrogen gas was 
given out. The greatest part of the prussian blue formed in that 
operation remains in solution in the liquid. It appears only 
when the liquid comes in contact with the air. This shows ua 
that prussian blue at a minimum of oxidizement is soluble in 
hydrocyanie acid. 
“ Dry hydrocyanic acid placed in contact with iron filings ~ 
undergoes no change in its colour nor smell; but the iron 
which becomes agglutinated together at the bottom of the vessel 
assumes a brown colour. After some days, the hydrocyanie 
acid being separated from the iron, and put in a small capsule 
under a glass jar, evaporated without leaving any residue. 
Therefore it had dissolved no iron. 
“ Hydrocyanic acid dissolved in water placed in contact with 
hydrate of iron, obtained by means of potash, and washed with 
boiling water, furnished prussian blue immediately without the 
. addition of any acid. Scheele has made mention of this fact. 
When hydrocyanic acid is in excess on the oxide of iron, the 
liquor which floats over the prussian blue assumes, after some 
time, a beautiful purple colour. The liquor, when evaporated, 
leaves upon the tists of the dish circles of blue, and others of @ 
purple colour, and likewise crystals of this last. colour. When 
