AEROLOGY. 
i54 
air; being in federal refpefts a medium betwixt the air 
procured from charcoal and that from iron. It contains 
about one-fourth of its bulk of uncombined fixed air, 
but not quite one-tenth intimately combined with the re¬ 
mainder. The water that came over -was blue, and pret¬ 
ty ftron'gly alkaline; owing to the volatile alkali not hav¬ 
ing been totally expelled by the heat which had reduced 
the bones to blacknefs. 
A variety of fubftances, faid not to contain any phlo¬ 
gifton, were lubjefted to the fame procefs, but without 
yielding' any inflammable air. The experiments with 
iron, however, were the mod fatisfa&ory, as being fub- 
jeft to lefs variation than thofe with charcoal; and clear¬ 
ly evincing, that the air in the procefs does not come from 
the water alone, but from the iron alfo ; or, as Dr. Prieft- 
ley fays, “ only from the iron;” the weight of water ex¬ 
pended, deducting the weight of air produced, being 
found in the addition of weight in the iron as nearly as 
could be expected in experiments of this kind. The quan¬ 
tity of inflammable air that may be procured by fleam 
from any given quantity of iron, the dadtor {fates thus : 
“ 960 grains of iron, when diflolved in acids, will yield 
about 800 ounce-meafures of air; but, treated in this 
manner, it yielded 1054 meafures, and then the iron had 
gained 329 grains in weight.” 
Inflammable air having been at firft produced only from 
metals by means of acids, it was then fuppofed that part 
of the acid neceffarily enters into its compolition ; but, as 
this hypothelis was proved to be ill grounded by the moft 
decifive experiments, we {hall not take up the reader’s 
time farther than by quoting Dr. Prielfley’s concluding re¬ 
marks on the fubjedt:—“ With refpedt to inflammable air 
(fays he) I have obferved, that when fufiicient care is 
taken to free it from any acid vapour that may be acciden¬ 
tally contained in it, it is not in the fmalleft degree affedl- 
ed by a mixture of alkaline air. On the whole, therefore, 
I have at prefent no doubt, but that pure inflammable air, 
though it certainly contains water , does not neceffarily 
contain any acid: yet an acid vapour may be ealily diflu- 
fed through it, and may perhaps, in many cafes, be ob- 
flinately retained by it, as no kind of air feems to be ca¬ 
pable of fo great a variety of impregnations as inflamma¬ 
ble air is.” ' 
We are indebted to Mr. Cavendifli for the fadt that 
water is neceflary to the produdtion of inflammable air, 
and to Dr. Prieftley for thedifcovery that charcoal is per- 
fedtly deflrudl'ible, or decompofed, in z’acuo, and, by the 
heat of a burning lens, almofl convertible into inflamma¬ 
ble air; nothing remaining befides an exceedingly fmall 
quantity of white afhes, which are fcarcely vifible. The 
great weight of afhes produced by burning wood in the 
open air arifes from what they attradf from the atmofphere. 
The air got in this manner is wholly inflammable, and 
without containing the leafl particle of fixed air; but, in 
order to this, the charcoal mull be made with fuch a heat 
as will expel all the fixed air from the wood; and it mud 
be-continued till it yield inflammable air only, which, in 
an earthen retort, is fcon produced. Wood or charcoal 
is even perfectly deftrudtible, that is, refclvable into in¬ 
flammable air, in a good earthen retort, and a fire that 
would about melt iron. An ounce of charcoal made from 
oak generally gives about five ounce-meafures of inflam¬ 
mable air in twelve minutes. 
The proofs of the agency of water, in the production 
of inflammable air, Dr. Prieftley communicates in the 
following words:—“ Apprifed of the influence of unper¬ 
ceived moifture in the production of inflammable air, and 
willing to afcertain it to my perfeCt fatisfadtion, 1 began 
with filling a gun-barrel with iron-filings in their common 
frate, without taking any particular precaution to dry 
them, and I found that they gave air as they had been ufed 
to do, and continued to do fo many hours: I even got ten 
ounce-meafures of inflammable air from two ounces of 
iron-filings in a coated giafs retort: at length, however, 
she production of inflammable air from the gun-barrel 
ceafed; but, on putting water to it, the air was produced 
again ; and a few repetitions of the experiment convinced 
me, that I had been too precipitate in concluding that in¬ 
flammable air is pure phlogifton. I then repeated the ex¬ 
periment with the charcoal, making the receiver the {land 
on which I placed the charcoal, and the charcoal itfelf as 
dry and hot as poflibie, and tiling cement inflead of wet 
leather, in order to exclude the air. In thefe circumftan- 
ces, I was not able, with the advantage of a good fun, 
and an excellent burning lens, to decompofe quite fo much 
as two grains of the piece of charcoal which gave me ten 
ounce-meafures of inflammable air; and this, I imagine, 
was effected by means of fo much moifture as was depo- 
fited from the air in its ftate of rarefaction,~and before it 
could be drawn from the receiver. To the production of 
this kind of inflammable air, therefore, 1 was now con¬ 
vinced that water is as eflential as to that from iron.” 
Of inflammable airs the dodtor obferves, that the dif¬ 
ference moft commonly perceived is, that fome of them 
burn with a lambent flame, white, yellow, or fometimes 
blue; while another kind always burns with an explofion, 
making more or lefs of a report when a lighted candle is 
dipped into it. The inflammable air extracted from me¬ 
tals by means of acids is of this laft kind; and that from 
wood, coal, or other inflammable fubftances, by means ot 
heat, belongs to the former. It has alfo been obferved, 
that thefe kinds of inflammable air have different fpecific 
gravities; the pureft, or that v^Ricli is extracted from iron, 
&c. being about ten times as light as common air; but 
fome of the other kinds net more than twice as light.—• 
This difference was for fome time attributed to a quantity 
of fixed air intimately combined with the heavier kinds, 
fo that it could not be difeovered by lime-water, -while 
the lighteft contained no fixed air at all. In order to af¬ 
certain this point, he had recourfe to decompolition; which 
was performed by mixing with the inflammable air to be 
tried, an equal quantity of common or dephiogifticated air, 
and then confining them in a ftrong giafs veft'el prevloufly 
filled either with water or mercury; making afterwards 
an eleftric fpark in fome part of the mixture by means of 
wires inferted through the lides of the velfel, and nearly 
meeting within it. Thus he fuppofed that he might be 
able to determine the quantity of combined fixed air, and 
likewife the relative quantity of phlogifton contained in 
each of them. The former appeared by waffling the air 
with lime-water after the explofion, and obferving how 
much of them wasabforbed ; and the latter by examining 
the refiduum with the tell of nitrous air, and obferving the 
purity of it. Finding, however, that in fome cafes more 
fixed air was found after the explofion than could have 
been contained in the inflammable air, he w as thence led to 
obferve the generation of fixed air from the principles men¬ 
tioned on another occalion. 
In profecuting this fubjeCt, it was found that one mea- 
fure of inflammable air produced by fleam from metals, 
and one of dephiogifticated air, fuch as by mixture with 
two meafures of nitrous airwas reduced to 0-72 of a mea- 
fure, were reduced by explofion to o - 6 of a meafure; 
the refiduum, by an equal quantity of nitrous air, was re¬ 
duced to 0-87. With the fame dephiogifticated air, the 
inflammable air from fining-cinder and charcoal w'as re-, 
duced only to 1-85 of a meafure ; but by waffling in lime- 
water, to 1-2. 1 he refiduum examined by nitrous air ap¬ 
peared to be of the ftandard of 0-9. In another procefs, 
the diminution after the explofion was to 1-55, and that af¬ 
ter waffling in lime-water to 0-65, of a meafure ; in a third 
by explofion, to 1 -6,and by waffling to o - 66 -, and in a fourth 
the firft diminution was to s-6, and the fecond to o - 6. In 
this laft experiment there was a generation of an entire 
meafure of fixed air ; and that this had not been contained 
originally in any latent {’rate in the original fluid, was evi¬ 
dent from the fpecific gravity of the inflammable air made 
life of. This, indeed, was one of the heaviell kinds of the 
fluid : but forty ounce-meafures of it weighed only two 
grains more than an equal bulk of common air; whereas, 
