92 Mr Granam on Phosphureited Hydrogen. 
fluence depended on something accidental and not essential to 
the gas. For instance, the hydrogen which comes over almost 
pure towards the end of the process for phosphuretted hydro- 
gen had none of this property, nor did it appear in hydrogen 
obtained from the following sources ;—from the electric decom- 
position of water, from the decomposition of steam by iron, from 
the action of water on amalgam of potassium, or from the action 
of muriatic, arsenic, or phosphoric acid on zinc. Even in the 
case of the action of sulphuric acid on zine or iron, which had 
first afforded hydrogen possessing the property in question, it 
turned out that only the hydrogen evolved at an early period 
of the action is efficient, while the gas evolved after the viva- 
city of the action is impaired is nearly, and sometimes entire- 
ly, destitute of any influence. The activity of the hydrogen was 
in short traced to a slight impregnation of nitrous acid vapour, 
which it possessed. The sulphuric acid of commerce always con- 
tains a small portion of some acid of nitrogen, probably the hy- 
ponitrous, from which, I find, it cannot be freed by boiling or 
concentration continued for any length of time. On quickly mix- 
ing sulphuric acid with two or three volumes of water, the pre- 
sence of nitrous acid is attested by its peculiar odour, and almost 
certainly by the appearance of brown fumes. ‘That the hydrogen 
did not owe the property in question to a trace of nitric oxide, 
which, combining with oxygen, might, by a slight consequent 
evolution of heat, have an effect in kindling the phosphuretted 
hydrogen, was proved by the fact, that the property in question 
could not be imparted to hydrogen by any proportion of nitric 
oxide ; but to this point there will be occasion to recur. 
At an earlier stage in the inquiry, some experiments were 
made upon the effect of other gases than hydrogen upon phosphu- 
retted hydrogen. None, with the exception of sulphuretted hy- 
drogen (evolved by the action of sulphuric acid'on. sulphuret of 
iron, and which therefore contains free hydrogen), appeared to 
favour the accendibility of the gas. On the contrary, the addi- 
