AERO 
It extinguifhed a candle; fo that the air came properly 
from the allies, and not from any remaining particles of 
the charcoal mixed with them. After the procefs, the 
allies weighed 839 grains; but, by expofure to the air for 
one day, the weight was increafed to 842 grains; and, 
perhaps, with more heat than before, yielded fifty ounce - 
meafures of air; of which about one-eighth was fixed air, 
and the ftandard of the reliduum 1-38 and 1-41. A can¬ 
dle burned in this refiduum, and the allies were reduced to 
7S9i grains. Dr. Prieltley afterwards fubjefted Hom- 
berg’s pyrophorus to fimilar trials, and the refults proved 
highly interelting, though they atforded no general con- 
clulion. 
Inflammable Air. 
We owe the knowledge of the exiftence, and of fome 
remarkable properties, of this air, to Mr. Cavendilh, by 
whom they were firft publilhed in 1767. Its eftefts, how¬ 
ever, had long before been fatally experienced by miners; 
in wliofe fubterraneous habitations it is often collected in 
fuch quantities as to produce the mod: dreadful eff'efls. It 
is produced in abundance from putrid animal and vege¬ 
table fubltances; and, in general, by all thofe which part 
with their phlogiflon ealily. 
Being much lighter than common air, it always rifes to 
the top of thofe places where it is generated; fo that it 
cannot be confined except in fome vaulted place, but al¬ 
ways drives to afcend and mix with the atmofphere. By 
itfelf it w ill indantly put an end to animal life; but, mixed 
with atmofpherical air, it may be breathed in much great¬ 
er quantity than fixed air. Its great inflammability in this 
date, however, renders it very dangerous to bring lights, 
or even to drike a flint with deel, in places where it 
abounds. Yet this only happens w hen inflammable air is 
mixed with common atmofpherical or with dephlogiflica- 
ted air; in which latter cafe, the explolion is by many 
degrees more violent; but pure inflammable air extin- 
guidies flame as effectually as fixed or phlogiflicated air. 
But, befides fubterraneous places, this kind of air is 
found in ditches; over the furface of putrid waters; in 
burying-grounds; in all places where putrid animal and 
vegetable matters are accumulated. In hot climates, 
tvhere putrefaction is mod prevalent, if the mud at the 
bottom of a pond be well dirred, and a lighted candle 
brought to the furface of the water, a flame will indantly 
fpread a confiderable way over the w'ater, from the afcen- 
fion of the inflammable air. In colder climates, though 
the generation of inflammable air is not fo plentiful, it 
may be ealily collected in a jar filled with water, and in¬ 
verted over a pond, the mud at the bottom being dirred 
with a dick. 
The meteors and ignes fatui , which are feen in warm 
climates, have been fuppofed nothing more than dreams 
of inflammable air fired in the atmofphere by eleCtric cx- 
plolions; but thefe appearances are accounted for in a 
more fatisfaCtory way. There is hardly any inflammable 
fubdance out of which this air may not be extracted, yet 
the fluids which go by the general name of inflammable 
air, have fcarcely any other property in common, belides 
thofe of inflammability, and being fpecifically lighter 
than atmofpherical air. ft is, however, neceflary to make 
a proper didinCtion between an inflammable gas, properly 
fo called, and that which is evidently made by combining 
an inflammable fubdance with common air ; which being 
eafily feparated leaves that fluid in the date it was before. 
By heat alone, a confiderable quantity of this kind of air 
may be extracted from molt inflammable fubltances, and 
even from fome of the metals. Dr. Priefiley obtained it 
from a vad number of fubltances, by diddling them in a 
gun-barrel, to the extremity of which was luted a tobac¬ 
co-pipe, with a flaccid bladder tied on the end. He ob- 
ferves, that the heat mult be fuddenly applied, in order 
to get a confiderable quantity of air from thefe fubflances. 
41 Notwithfianding (fays he) the fame care be taken in lu¬ 
ting, and in every other refpeCt, fix, or even ten, times 
Vol. I. No. 10. 
more air may be got by a fudden heat than by a flow one, 
though the heat that is lad applied be as intenfe as that 
which was applied fuddenly. In a trial of the metallic 
calces he had no fuccefs. 
In the infancy of his experiments, Dr. Priefiley ima¬ 
gined, that the inflammable air produced in this way came 
only from the metal; while Lavoilier, on the other hand, 
attempted to prove that it proceeded almofl exclufively 
from the water. The method which the latter had fol¬ 
lowed, was to fend the deam of boiling water through 
a red-hot iron tube; in doing which the intenfe heat ac¬ 
quired by the water occafioned the production of a great 
quantity of inflammable air. Dr. Priefiley repeated his 
experiments not only with water, but with other fluids. 
Sending the vapour of two ounces of fpirit of wine thro’ 
a red-hot earthen tube, he obtained 1900 ounce-meafures of 
inflammable air, which burned with a white lambent 
flame. It contained no fixed air ; and thirty ounce-mea- 
fures of it weighed eight grains lefs than an equal quantity 
of common air. He collected alfo 0-3 5 of an ounce-mea- 
fureof water. In this experiment the w eight of the wa¬ 
ter collected was 168 grains, of the inflammable air 633 
grains, and that of the fpirit of wine originally was 821 
grains; fo that as little was loft in the procefs as could be 
expeCted. Repeating the experiment with vitriolic ether, 
an ounce of it treated in the lame manner in an earthen 
tube almolt filled with pieces of broken earthen retorts 
and crucibles, one-tenth part of an ounce of water was 
collected, and 740 ounce-meafures of inflammable air 
were procured, without any mixture of fixed air, burn¬ 
ing with a white lambent flame like that of wood, and 
not exploding with dephlogifiicated air. Twenty-nine 
ounce-meafures of this weighed five grains lefs than an 
equal quantity of common air. Vapour of fpirit of tur¬ 
pentine yielded inflammable air mixed with much black 
fmoke, which foon collected on the furface of the water 
in the receiver. The fmell of this air was exceedingly 
offenfive, and its flame was much lefs luminous than that 
of the former. Its fpecific gravity was the fame with that 
of the air procured from fpirit of wine. Olive oil yield¬ 
ed a confiderable quantity of air on being mixed with cal¬ 
cined whiting; the firft portions burning with a large 
white flame, and the lad with a lambent blue one. 
In extracting air from folid fubflances, the deam of 
water was always neceflary; and thus inflammable air was 
produced from a great number of different ones. From 
f ulphur treated in this manner in an earthen tube, inflam¬ 
mable air was obtained of a nature fimilar to that from 
oil of vitriol and iron. From arfenic the produce was 
one-feventh of fixed air; but all the red flrongly inflam¬ 
mable, with a fmell fcarcely didinguifhable from that of 
phofphorus. Twenty ounce-meafures of this air weigh¬ 
ed four grains and a half lefs than an equal quantity of 
common air. Both thefe experiments, however, were 
very troublefome, on account of the volatility of the mat¬ 
ters, which fublimed and choaked up the tubes. From 
two ounces of fcales of iron, or fining cinder, which he has 
found to be the fame thing, Dr. Priefiley obtained 580 
ounce-meafures of air; one-tenth of the firfl part of 
which was fixed air, but afterwards it was all inflamma 
ble. Forty ounce-meafures of this air weighed two grains 
more than an equal quantity of common air. From char¬ 
coal expofed to the red-hot deam of water, inflammable 
air was procured in great quantities. From ninety-four 
grains of perfect charcoal, that is, prepared with a flrong 
heat fo as to expel all fixed air from it, and 240 ounces of 
water, 840 ounce-meafures of air were obtained, one- 
fifth part of which was fixed air; and the inflammable 
part appeared iikevvife, by decompolition, to have a quan¬ 
tity of fixed air intimately combined with it. Three oun¬ 
ces of bones burnt black, and treated in this manner in a 
copper-tube, yielded 840 ounce-meafures of air; the wa¬ 
ter expended being 288 grains, and the bones lofing 110 
grains of their v.'eight. This air, he obferves, differs 
conliderably from that of any other kind of inflammable 
