Mr Grauam on Phosphuretted Hydrogen. 103 
the same gas, may be promoted by the presence of nitrous acid, 
which will explain Dr Tuomson’s experiments. 
The impregnating nitrous mixture of the foregoing experi- 
ments was not destitute of nitric oxide, but what proves that the 
efficiency of the mixture did not depend upon the last mentioned 
ingredient, is the circumstance, that the mixture lost its virtue 
by standing over mercury for a week, during which period the 
acid-vapour was absorbed by the mercury, but the nitric oxide 
remained, as appeared on admitting air to the gaseous mixture. 
Hence, we may conclude, that when nitric oxide acts in produ- 
cing inflammability in phosphuretted hydrogen, it is from the ni- 
trous acid which it occasionally contains. 
It is certainly, however, very curious that nitric oxide is not 
quite equivalent to nitrous acid, in producing the change in ques- 
tion upon phosphuretted hydrogen, seeing that the nitric oxide 
passes immediately into nitrous acid upon meeting air. Whether 
the negative influence of nitric oxide upon really accendible gas 
is sufficient to account for this anomaly, I am doubtful. It may 
be thought that nitrous acid and phosphuretted hydrogen, when 
in contact for a short time, react upon each other, with the pro- 
duction of some entirely new and highly accendible body. But 
this supposition seems not to quadrate with the fact, that the im- 
pregnating mixture requires to be diluted by so large a propor- 
tion of phosphuretted hydrogen, before the whole becomes spon- 
taneously accendible. Nor is it supported by any visible signs 
of reaction between the nitrous acid and phosphuretted hydrogen. 
Indeed, nitrous acid-vapour appears to be compatible with phos- 
phuretted hydrogen, to an extent which could not have been an- 
ticipated. 
Again, that nitrous acid, or at least some acid compound of 
nitrogen, continues to exist in what we may now call the nitrous 
phosphuretted hydrogen gas, appears to be corroborated by the 
properties which this self-accendible gas is found to possess. 
