C I 7 2 3 
flammable air is the very fame, as far as I am able to 
perceive,, from whatever fubftance of the fame 
kingdom it be extracted* Thus it makes no differ- 
ence whether it be got from iron, zinc, or tin, from 
any kind of wood, or, as was obferved before, from 
any part of an animaL 
If a quantity of inflammable air be contained in a 
glafs veffel ftanding in water, and have been gene- 
rated very faft, it will fmell even through the water, 
and this water will alfo foon become covered with a 
thin film, affuming all the different colours. If the 
inflammable air have been generated from iron, this 
matter will appear to be a red okre, or the earth of 
iron, as I have found by collecting a confiderabie 
quantity of it; and if it have been generated from 
zinc, it is a whitifh fubftance, which I fuppofe to be 
the calx of the metal. It likewife fettles to the 
bottom of the veffel, and when the water is ftirred, 
it has very much the appearance of wool. When 
water is once impregnated in this manner, it will 
continue to yield this fcum for a confiderabie time 
after the air is removed from it. This I have often 
obferved with refpeCt to iron. 
Inflammable air, made by a violent eftervefcence, I 
have obferved to be much more inflammable than 
that which is made by a weak effervefcence, whe- 
ther the water or the oil of vitriol prevailed in the 
mixture. Alfo the offenfive fmell was much, 
ftronger in the former cafe than in the latter. The 
greater degree of inflammability appeared by the 
greater number of fucceflive explofions,when a candle 
was prefented to the neck of a phial filled with it. 
It is poflible, however, that this diminution of in- 
flammability 
