LS eS ae 
Cyanogene or Prussine. 153 
cyanide is dissolved in water, it is changed into the hydro- 
cyanite, for the hydrocyanic acid is certainly formed,wheth- 
er by the decomposition of water, orotherwise. —- 
When the solution of the cyanide of potash in’ water, 
whatever change it may have undergone during its solution, 
is added to a salt of iron in which the metal is peroxydized, 
as in the persulphat of iron, the precipitate which is formed 
is the perferrocyanite of iron. Admitting the formation of 
hydrocyanic acid in the first instance, we would infer, that, 
when brought in contact with the salt of iron, the acid it- 
self is decomposed, or in other words is changed into the 
ferrocyanic acid, before its union with the oxyd of iron. 
Porret, however, considers the ferrocyanic acid as a com- 
pound of iron, oxydized to the minimum, and hydrocyanic 
acid. The conclusion of Dr. Thomson was, that it was mere- 
ly a compound of metallic iron and cyanogene, but he sub- 
sequently inferred, that it is composed of iron and ne Ges y- 
ic acid. When the cyanide of potash is dissolved in wa- 
r, and added to the sulphate of the plus oxydized iron, we 
obtain a due precipitate, but if we employ the protosul- 
phate, properly so called, the result is a white precipitate, 
which may be converted into the blue ferrocyanite either 
by exposure to the atmosphere, or by the affusion of an 
acid. If we admit that metallic iron enters into the com- 
such proportions as to formit. This indeed may be the 
fact in sundry other processes ; as, for instance, in the pu- 
Vou. VI....No. I. 20 
