Mr. Davy on some 
1 16 
limited, appears from this circumstance, that the addition of a 
little nitrous acid to the sulphate, entirely prevents the forma- 
tion of the black powder, though successive portions of alco- 
hol be added, and the whole boiled for a considerable time. 
When sulphate of platinum, containing a little nitrous acid, 
is treated with alcohol, a mutual action takes place ; slowly 
at the common temperature of the air ; but rapidly by the 
assistance of heat : the sulphuric acid being united to the 
oxide of platinum by a weak affinity, seems to form a new 
combination with the alcohol, whilst the oxide combines with 
the portion of nitrous acid present, to form the black pow- 
der. In certain cases, as is well known, alcohol separates salts 
from their aqueous solutions, in consequence of a stronger 
affinity for the water in which they are dissolved; but in this 
instance, the agencies of alcohol and of nitrous acid, are 
probably concerned in separating the sulphuric acid from 
the sulphate. 
The vivid action of ammoniacal gas on the powder, may 
be referred to the-mutual energy with which the alkaline gas, 
and loosely combined nitrous acid in the powder, act upon 
each other. I found by experiment, that ammoniacal gas is 
absorbed in this instance; thus, 3 grains of the powder were 
placed in a graduated glass receiver, and filled with dry mer- 
cury. 2*3 cubic inches of ammoniacal gas, containing only 
impurity, were let up into the receiver : an immediate 
action took place, the powder became ignited, and after two 
hours, of a cubic inch of the gas were absorbed ; recently 
boiled pure water, whilst yet hot, was let up into the receiver, 
and the residual gas was all absorbed, except a small 
globule, which did not exceed the original impurity in the 
ammonia. 
