£ 170 1 . .. 
plant had been growing in the burned air from the 
8 th of the fame month. Refides, the plant which I 
have found to be the moft effectual of any that I 
have tried for this purpofe is fpinach, which is of 
quick growth, but will feldom thrive long in water. 
One jar of burned air was perfectly reftored by this 
plant in four days, and another in two days. This 
laft was obferved on the 2 2d of July. In general 
this effeCt may be prefumed to have taken place in 
much lefs time than I have mentioned ; becaufe I 
never chofe to make a trial of the air, till I was 
pretty fure, from preceding obfervations, that the 
event which I had expe&ed mull have taken place, 
if it would fucceed at all ; left, returning back that 
part of the air on which I made the trial, and which 
would thereby neceffarily receive afmall mixture of. 
common air, the experiment might not be judged 
to be quite fair ; though I myfelf might be fuffici- 
ently fatisfed with refpedt to the allowance that was 
to be made for that fmall imperfection. 
II L 
Of inflammable Air. 
I have generally made inflammable air in the 
manner defcribed by Mr. Cavendifh, in the Philofo- 
phical Tranfadtions, from iron, zinc, or tin ; but 
chiefly from the two former metals, on account of 
the procefs being the leaft troublefome : but when' 
X extradted it from vegetable or animal fubftances,, 
or from coals, I put them into a gun barrel, to the 
orifice of which I luted a glafs tube, or the ftem of 
a to- 
