and Sulphuretted Prussiates. 17 
mosphere. They then lose not only their water of crystalliza- 
tion, but also that which is produced by the combination of the 
hydrocyanic or prussic acid with the oxygen of the two bases ; 
and there remains a double cyanuret, composed of one atom of 
cyanuret of iron, with two atoms of cyanuret of the other metal. 
The same thing also takes place with the ferruginous prussiates 
of lead and silver. 
When these cyanurets are burned with the oxide of copper 
in a suitable apparatus, they give no water. The double cya- 
nuret of iron and lead yields carbonic gas and azotic gas in the 
proportion of ^ to 1 ; but those of potassium and barium yield 
them in the proportion of 3 to S, because the base retains one- 
fourth of the carbonic acid, forming a species of double salt of 
carbonate and cuprate of potash or barytes. The prussiate of 
iron and ammonia is riot capable of being reduced to a double 
cyanuret. When distilled, it yields prussiate of ammonia, and 
a little water formed by the conversion of prussiate of iron in- 
to a cyanuret. The cyanuret afterwards decomposes and gives 
out azotic gas, leaving as a residue a carburet of iron, composed 
of 4 atoms of carbon and 1 atom of iron. Thfe carburet presents 
a very remarkable phenomenon : when heated to redness in the 
retort, it takes fire, and appears to burn as in oxygen gas, 
though the gas which surrounds it is only azotic gas, and though 
it experiences no alteration. The flame lasts only for an instant: 
It is analogous to that which is exhibited with oxide of iron, 
and that of chrome, zircon, &c. when they are heated to redness, 
after having taken away from them their water of combination. 
This same phenomenon is observed in the distillation of several 
of the ferruginated prussiates, particularly in that of Prussian 
blue. The acid substance called by Mr Porret^the Ferruretted 
Chyazic Acid, is, according to M. Berzelius, a prussiate acid of 
the protoxide of iron, where the base is combined with three 
times as much acid as in the neutral prussiate. 
M. Berzelius prepares this acid salt in decomposing the prus- 
siate of iron and lead under water, by means of a current of sul- 
phuretted hydrogen gas. The hepatic liquid is put in contact 
with a new portion of prussiate, in order to remove the sulphu- 
retted hydrogen in excess ; it is then filtered, and evaporated in 
vacuo. 
VOL. TV. NO. 7. JANUAIIY 1821. B 
