AND OF SALTS OF THE PEROXIDE OF IRON. 
259 
it appears to have no action, but on evaporating the mixture 
to dryness, and warming the residue so as to disengage am- 
monia, the mass becomes strongly blue. No change of color 
ensues previous to the disengagement of ammonia. 
The behaviour of nitrate of ammonia to the cyanide is like- 
wise remarkable; if some of the salt be heated to fusion, and 
a few crystals of the ferridcyanide of potassium conveyed 
into the liquid mass, it immediatety becomes of a dark blue, 
and there is a strong smell of prussic acid. If the mixture 
is still further heated, it assumes a reddish-yellow color, and 
now affords no further precipitate either with a persalt or 
protosalt of iron ; but if the mass, while still blue, is treated 
with water, the filtered solution gives prussian blue with ni- 
trate of iron. If a solution of the percyanide is added to one 
of neutral sulphate of ammonia, and the whole is evaporated 
to a pasty mass, it appears green. If it be now heated to 
fusion, it acquires a light blue color, and if some water be 
poured over the mass thus treated, it becomes deep blue, and 
there is a separation of prussian blue. The filtered liquid is 
not rendered perceptibly blue by nitrate of iron. 
If a few drops of hyponitric acid are added to a mixture of 
ferridcyanide of potassium and nitrate of iron, there is a pre- 
cipitate of prussian blue. Since pure nitric acid produces no 
change in the above mixture, this reaction may be employed 
to detect even small quantities of nitrous acid in nitric acid. 
Nitric oxide has a very energetic action on a mixture of per- 
cyanide and nitrate of iron ; each bubble of this gas, on en- 
tering the solution, becomes surrounded with a blue coating, 
and prussian blue is very rapidly thrown down. Nitrous 
oxide behaves with perfect indifference towards such a mix- 
ture. 
Sulphurous acid likewise possesses in a high degree the 
power of altering the dissolved percyanide in such a manner 
that it shall afford blue precipitates with persalts of iron. 
Since the precipitation of prussian blue by the nitrous acid, 
nitric oxide and sulphurous acid from a solution of the above- 
