256 DEOXIDATION OF FERRIDCYANIDE OF POTASSIUM, 
tosalt. The more readily oxidized metals, such as zinc, 
iron, tin, &c, give rise to formation of prussian blue under 
the above-mentioned circumstances in a two-fold manner. 
These metals quickly convert a portion of the percyanide 
into protocyanide, and a portion of the persalt of iron into 
protosalt. 
The fact that even most carefully-cleansed plates of pla- 
tinum, palladium and gold produce prussian blue when a 
mixture of the aqueous solutions of ferridcyanide of potassium 
and pernitrate of iron is brought on to them, is highly re- 
markable. It is true that the change in this case takes place 
very slowly. 
We are therefore apparently justified in concluding that 
all metallic bodies, without a single exception, are capable of 
producing the same effect on the haloid salt. If the solution 
of the cyanide be poured over finely-divided protoxide of 
copper or protoxide of tin, and both substances left only for 
a short time together, the filtered liquid is rendered strongly 
blue on the addition of pernitrate of iron. Probably other 
oxides, which have a greater inclination to combine with 
more oxygen, behave in a similar manner. 
But it is not only the metallic bodies or certain metallic 
compounds which are capable of exerting a chemical influ- 
ence of the kind previously described on the solution of the 
ferridcyanide, but a series of non-metallic substances like- 
wise exhibits a similar behavior. If phosphorus be held for 
some length of time in contact with the solution of the per- 
cyanide, the latter acquires the property of becoming blue 
(only indeed in a faint degree) on the addition of a solution 
of peroxide of iron. But if a piece of phosphorus be held in 
a mixture of percyanide and solution of a persalt of iron, and 
be allowed to remain some time in the liquid or exposed to 
the atmosphere, it becomes surrounded with a coating of 
prussian blue. This phenomenon appears, however, to be 
principally owing to the persalt of iron being partially con- 
verted by the phosphorus into a protosalt. Schonbein passed 
