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, or otherwise. 



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 perosydized, 

 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 hydrocy- 

 anic acid. When the cyanide of potash is dissolved in wa- 

 ter, and added to the sulphate of the plus oxydized iron, we 

 obtain a blue 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 me/a//{c iron enters into the com- 

 position of ferrocyanic acid, we would infer, that part of 

 the hydrogen of the hydrocyanic acid, unites with a part of 

 the oxygen of the oxydized iron, by which the iron is redu- 

 ced, and the metallic iron then unites with the cyanogen 

 and the remaining hydrocyanic acid, formerly the ferrocy- 

 anic acid ; which, by uniting with the undecomposed oxyd 

 of iron, produces the perferrocyanite or Prussian blue. It 

 is known, however, that the Prussian blue used as a pig- 

 ment, is a mixture of the perferrocyanite and allumina, in 

 consequence of the addition of alum, which is made previ- 

 ously to the precipitation. 



As prussic acid may be obtained by distilling peach 

 blossoms, bitter almonds, &;c. it is evident, that the veget- 

 able kingdom will also yield it ; and in many processes of 

 art, the elements of cyanogene may frequently combine in 

 such proportions as to form it. This indeed maybe the 

 fact in sundry other processes ; as, for instance, in the pu^ 



Vol. VI....N0. 1. 20 



