100 Mr Grauam on Phosphuretted Hydrogen. 
the gas. When nitric acid is brought into contact with the gas 
in this manner, a violent action occurs ; but with nitrous acid the 
evolution of white fumes is very slight. The nitrous acid is ab- 
sorbed in part by the mercury, but this absorption is slow, pro- 
vided the quantity of gas be considerable with which the acid 
vapour is mixed. If the quantity of gas primarily impregnated 
with nitrous acid, in the manner described, be small, or the im- 
pregnation of nitrous acid considerable, the gas exhibits no dis- 
position to smoke or to take fire, when passed into air. It has 
not become spontaneously accendible. On diluting the gas with 
a large proportion of unimpregnated phosphuretted hydrogen, no 
reaction is indicated, but the whole becomes spontaneously ac- 
cendible in a high degree. In fact, it was discovered that the 
gas is not accendible when the nitrous acid exceeds a certain pro- 
portion, which is by no means considerable. 
(2.) Allow a single drop of nitrous acid to fall into a dry 
glass jar, which may be of small dimensions. Fill the jar with 
mercury, and invert it without loss of time in the mercurial 
trough, a bubble of gas will collect in the upper part of the jar, 
which bubble is chiefly nitrous acid vapour. One cubic inch or 
so of phosphuretted hydrogen, or of hydrogen itself, may then be 
added to the gas in the jar, and this is our nitrous impregnating 
mixture. Suppose this mixture to contain one-twentieth of its 
bulk of nitrous acid vapour. The addition of it, in any propor- 
tion, to phosphuretted hydrogen, is not attended by the slightest 
production of white fumes ; in fact no reaction appears to take 
place. But the addition of a single bubble of this mixture, not 
exceeding one-tenth of an inch in volume, to five or six cubic 
inches of phosphuretted hydrogen, will render the whole highly 
accendible, so that every bubble passed into the air will take 
fire. 
(3.) In the above arrangement, a drop of the strongest nitric 
acid may be substituted for the nitrous acid, in the preparation 
of the impregnating mixture. The nitric acid acts on the mer- 
