258 DEOXIDATION OF FERRIDCYANIDE OF POTASSIUM, 
ide, the mixture soon begins to turn blue, and after some 
days a considerable precipitate of the most beautiful prussian 
blue has formed. It is therefore evident that the aether or 
alcohol has either changed the percyanide into protocyanide 
or the persalt of iron into protosalt. 
If ordinary sugar be added to the solution of percyanide, 
and the liquid be kept boiling for a few minutes, it is turned 
blue on mixing pernitrate of iron with it. The mixture will 
also appear blue if some of the salt of iron is added to it ; 
after some hours, without any exposure to heat, and after 
some days there will be a considerable deposit of prussian 
blue. 
When the solution of percyanide is mixed and warmed 
with formic acid, it becomes blue without requiring any per- 
salt of iron ; if the mixture be evaporated until all acid is 
expelled and the residue extracted with water, this extract 
will afford with solution of nitrate of iron a precipitate of 
prussian blue. The same reaction takes place in the cold, 
only more slowly. Acetic, tartaric and citric acids act in a 
similar manner on the solution of cyanide, and probably 
several other organic acids. Oxalic acid appears to have no 
action either at the ordinary or at an increased temperature. 
Uric acid is remarkable, above all other organic compounds, 
from its quick action on this salt. If it has stood for only a 
minute with a solution of percyanide, this is rendered blue 
on the addition of nitrate of iron. A solution of creosote in 
water has perhaps a stronger action ; on shaking it for a few 
instants with a solution of percyanide, and then adding a 
persalt of iron, it is rendered strongly blue. If the excess 
of creosote has been expelled from the solution by heat, ni- 
trate of iron causes a very considerable precipitate of prussian 
blue. 
Cinchonine and morphine behave similar to uric acid and 
creosote, while strychnine and quinine appear to have no 
action. 
When urea is conveyed into a solution of the percyanide, 
