i4* AERO 
the operation. The fact, indeed, becomes fomewhat 
dubious from fome experiments related by Dr. Prieftley 
hhnfelf, and of which we fhall now proceed to give an 
account. 
One confequence of the hypothefis in queftion is evi¬ 
dent, that, if water really be produced by the deflagration 
of either dephlogifticated or common air with inflamma¬ 
ble air, the quantity of liquid obtained ought to increafe 
in proportion to the quantity of the two airs confumed, 
and that without any limitation. This, however, is not 
the cafe; and Dr. Prieftley deferibes as the greateft diffi¬ 
culty he ever met, with regard to the preceding theory, 
Iris never having been able to procure any water when he 
revived red precipitate in inflammable air; or at lead not 
more than might have been fuppofed to exifl in the inflam¬ 
mable air as an extraneous fubftance.—“ The difficulty 
(fays he) with refpeft to what becomes of the two kinds 
of air, was not leflened by the attempts which I made to 
collect all that I could from repeated decompolitions of 
inflammable and dephlogifticated air in a clofe veflel. As 
I had produced water in this procefs when no more than 
a Angle exploflon was made at a time, I thought that, by 
continuing to make exploflons in the fame velfel, the wa¬ 
ter would not fail to accumulate till any quantity might be 
colleffed; and I intended to have collefted a conliderable 
part of an ounce. And, as I ftiould know exactly what 
quantity of air I decompofed, I had no doubt of being 
able- to afeertain the proportion that the water and air 
bore to each other. With this view a mixture wuts made 
of a large quantity of air, ^ dephlogifticated, and § inflam¬ 
mable, from iron and oil of vitriol. But, though I had a 
fenfible quantity of water at the firft exploflon (in each of 
which between four and five ounce-meafures of the mix¬ 
ture of air were ufed), I wasfurprifed to perceive no very 
fenfible increafe of the quantity of w-ater on repeating the 
exploflons. Having therefore expended forty-eight ounce- 
meafures of the mixture, the procefs was difeontinued ; 
and, collecting the water with all the care that I could, I 
found no more than three grains, when there ought to have 
been ii.”-—In this procefs, the infide of the veil'd was al¬ 
ways very black after each exploflon : and there blued 
from the mouth of it a denfe vapour, which the doftor 
took fome pains to colled and examine, but without effect. 
“ That water, in great quantities, (fays he,) is fome- 
times produced from burning inflammable and dephlogif¬ 
ticated air, is evident from the experiments of Melfrs. 
Cavendilh and Lavoifier. I have alio frequently collect¬ 
ed considerable quantities of water in this way, though 
never quite fo much as the weight of the two kinds of air 
decompofed. My apparatus for this purpofe was the fol¬ 
lowing : Into the mouth of a large glafs balloon I intro¬ 
duced a tube, from the orifice of which there continually 
iflued inflammable air from a velfel containing iron and 
oil of vitriol. This, being lighted, continued to burn like 
a candle. Prefently after the lighting of it, the infide of 
the balloon always became cloudy, and the moifture foon 
gathered in drops, and fettled in the lower part of the 
balioon. To catch what might iffue in the form of va¬ 
pour, in the current of air through the balloon, I placed 
a glafs tube in which I always found fome water conden- 
fed. It is very poffible, however, that in both thefe modes 
of experiment the water may be converted into a kind of 
vapour very different from ftcam, and capable of being 
conveyed a great way through air, or even water, with¬ 
out condenfation along with the air with which it is mix¬ 
ed ; and on this account it may not be poffible, in either 
of thefe modes, to colled ad the waiter into which the two 
kinds of air may be converted. The nature of this kind 
of vapour into which water may be changed, and which 
is not readily condenfed by cold, is very little underftood, 
but well deferves the attention of philofophers.” 
That the water collected in the balloon comes from the 
decompofition of the air, and not from the frefli air cir¬ 
culating through it, was evident from placing balls of hot 
iron in the place of the flame, and finding, that, though 
LOGY. 
the balloon was as much heated by them as by the flame 
of the burning of the inflammable air, and confequently 
there muff have been the fame current of the external air 
through it, no moiffure was found in the balioon. 
Of Phlogi/licatcd Air. 
The univerfal opinion in favour of the exiffenceof that 
principle named phlogifon, firff fuggefted by Stahl, gave 
rife, on the appearance of Dr. Prieffley’s difeoveries, to 
a theory, concerning the attion of this fubftance upon air 
and other bodies. As it has been obferved, that air was 
diminilhed, in fome cafes at ieaft, by burning, univerfal- 
ly by refpiration, and by fome other proceffes, it was ima¬ 
gined, that phlogifton was a body of fuch a lingular nature, 
that, when mixed with air, it always diminifhed, inllead 
of enlarging, its bulk, as might be more naturally ex¬ 
pedited from the addition of any vapour whatever. It 
'was alfo fuppofed by fome, that phlogifton was not only 
entirely devoid of gravity, but that it was a principle of 
pofitive levity ; fo that the abfolute weight of bodies was di- 
miniffved by an union with it, and augmented when it- was 
expelled, though their fpccific gravity was diminilhed. 
Various other furprifing properties were attributed to 
phlogifton; fuch as that of giving elafticity to air, of con- 
ftituting flame by a chemical combination with air, &C. Its 
emiilion into the atmofphere was fuppofed to be always 
attended with a diminution of air; and, therefore, all pro¬ 
ceffes in which air was diminilhed and become noxious, 
fuch as that by liver of fulphur, a mixture of iron-filings 
and brimftone, See. were called phlogijlicproceffes. Refpi¬ 
ration of animals was taken into the fame account; but 
neither in this, nor in combuftion, was it allowed that any 
kind of vital fpirit was abforbed by the blood, or fepara- 
ted from the air by the burning body. On the contrary, 
it was ftrenuouffy argued, that all this was performed by 
the emifjion of phlogifton from the lungs or the inflamed fub- 
ftance, which depraved the air, and diminifhed it in bulk; 
and, as ali air was fuppofed to contain phlogifton, it was 
likewife imagined, that in all cafes, where air was mend¬ 
ed, as by the growing of vegetables, or agitation in water, 
the emendation was accomplifhed, not by the emiflion of 
any thing into the atmofphere, but by the mere abforp- 
tion of phlogifton. In other refpefts this fubftance was 
thought to be an exceedingly powerful principle in nature; 
the light of the fun itfelf and the eledric fluid being faid 
to be modifications of it, the different kinds of airs to be 
phlogijlic vapours, ( 3 c. fo that the whole fyftem of nature 
feemed ready to be abforbed by it at once- 
The formidable powers of this principle were firft check¬ 
ed by Lavoifier, though the latter erred equally on the 
contrary fide ; and, not content with keeping the phlogiftic 
principle within due bounds, would needs deny its exift- 
ence altogether. We accordingly find in a Treatife pub- 
lifhed in <783, he firft impugns Dr. Prieftlev’s theory of 
refpiration, and denies that i( the refpiration of animals 
has the property of phlogifticating air in a manner fimilar 
to what is effected by the calcination of metals and many 
other chemical proceffes; and that it ceafes not to be ref- 
pirable till the inftant when it becomes, furcharged, or at 
Ieaft faturated, with phlogifton.” 
In order to difprove this affertion, he introduced four 
ounces of mercury to fifty cubic inches of common air, 
propoling to calcine the metal by keeping it for twelve 
days in a heat almoft equal to that which is neceftary to 
make it boil. After the expiration of the appointed time, 
forty-five grains of precipitate per J'e were formed, and 
the air in the velfel was diminilhed about one-eighth of its 
volume. In this Hate it did not precipitate lime-water; 
but inftantly extinguifned candles, and killed animals im- 
merfed in it; no longer affording any red vapours, or be¬ 
ing diminilhed by mixture with nitrous air. On diftilling 
the precipitate produced, about as much dephlogifticated 
air was obtained as had been left by the common air in the 
calcination; and, by recombining this with the noxious 
air left ia the veflel, he re-compofed a fluid nearly of the 
fame 
