AEROLOGY. 
150 
bination of the two, in order to produce nitrous acid. It 
was alfo found, by the laft experiment, that the quantity 
of nitre produced was the fame that would have been ob¬ 
tained front the foap-leys, had they been faturated with 
nitrous acid; which (hews that the produdtion of the ni¬ 
tre was not owing to any decompofition of the foap-leys. 
“ As far as the experiments hitherto publifhed extend, 
we fcarcely know more of the nature of the phlogifticated 
part of the atmofphere, than that it is not diminifhed by 
lime-water, cauftic alkalies, or nitrous air; that it is un¬ 
fit to fupport fire, or maintain life in animals; and that its 
fpecific gravity is not much lefs than that of common air: 
fo that, though the nitrous acid, by being united to phlo- 
gifton, is converted into air poffeffed of thefe properties; 
and, confequently, though it was reafonable to fuppofe, 
that part at leaf! of the phlogillicated air of the atmof¬ 
phere confifts of this acid united to phlogifton; yet it 
might be fairly doubted whether the whole is of this kind, 
or whether there are not, in reality, many different fub- 
ftances confounded by us under the name of phlogifticated 
air. I therefore made an experiment to determine whe¬ 
ther the whole of a given portion of the atmofphere could 
be reduced to nitrous acid, or whether there was not a 
part of a quite different nature from the reft, which 
w'ould refufe to undergo that change. For this purpofe, I 
diminilhed a mixture of dephlogifticated and common air, 
till it was reduced to a fntall part of its original bulk; 
after which fome dephlogifticated air was added, and the 
fpark continued till no further diminution took place. 
Having by thefe means condenfed as much as I could of 
the phlogifticated air, I let up fome folution of liver of 
fulphur to abforb the dephlogifticated air; after which 
only a fmall bubble of air remained unabforbed, which 
certainly was not more than -j-L-th of the bulk of the 
phlogifticated air let up into the tube; fo that, if there is 
any part of the phlogifticated air of our atmofphere which 
differs from the reft, and cannot be reduced to nitrous 
acid, we may fafely conclude that it is not lhore than -jAgth 
part of the whole.” 
Though thefe experiments had fiiewn, that the chief 
caufe of this diminution of airs is the converiion of the 
phlogifticated kind into nitrous acid, it feemed not unlike¬ 
ly, that, when any liquor containing inflammable matter 
was in contact with the air in the tube, fome of this mat¬ 
ter might be burnt by the fpark, and thereby diminiih the 
air. In order to determine this, the electric fpark was 
palled through dephlogifticated air included between dif¬ 
ferent liquors; and the refult of the experiments was, 
that when dephlogifticated air, containing only one-twen¬ 
tieth part of its bulk of phlogifticated air, was confined 
between fiiort columns of foap-leys, and the fpark palled 
through it till no farther diminution could be perceived, 
the air loft a^ths of its bulk; which is not a greater di¬ 
minution than might very likely proceed from the decom¬ 
pofition of the fmall quantity of phlogifticated air con¬ 
tained in it, as the dephlogifticated air might be eafily 
mixed with a fmall quantity of common air while putting 
into the tube. When the fame deplogifticated air was 
confined between columns of diftilled water, the diminu¬ 
tion was rather greater than before, and a white powder 
was formed on the furface of the quickfilver beneath : the 
reafon of which, in all probability, was, that the acid 
produced in the operation corroded the quickfilver, and 
formed the powder; and that the nitrous air produced by 
that corrofion united to the dephlogifticated air, andcau- 
fed a greater diminution than would otherwife have taken 
place. When a folution of litmus was ufed inftead of 
diftilled water, the folution loon acquired a red colour; 
which grew paler and paler as the fpark was continued, 
till it became quite colourlefs and tranlparent. The air 
was diminifhed by almoft one-half, and might perhaps 
have been further diminiftied had the fpark been continu¬ 
ed. When lime-water was let up into the tube, a cloud 
was formed, and the air was further diminifhed by about 
one-fifth; the remainder was good dephlogifticated air.. 
In this experiment, therefore, the litmus was, if not burnt,, 
at leaft decompounded, fo as to lofe entirely its purple 
colour, and to yield fixed air; fo that, though foap-leys 
cannot be decompounded by this procefs, yet the folution 
of litmus carr, and fo very likely might the folutions of’ 
many other fubftances. But there is nothing in any of 
thefe experiments which favours the opinion of the air 
being at all diminifhed by means of phlogifton communi¬ 
cated to it by the electric fpark. 
Of Fixed Air. 
The difeovery of this kind of air is as old as Van- Hel- 
mont, w ho gave it the name of gas filvejtre , from its being 
emitted in great quantity by burning charcoal. Subic* 
quent difeoveries fhewed, that a fluid of the fame kind 
was plentifully produced by fermenting liquors, by almoft 
every kind of combultion, and was alfo naturally gene¬ 
rated, in vaft quantity, in mines and coal-pits, where it is 
known by the name of the choak-clamp-, that it exirts in a 
concrete ftate in alkaline falts, chalk, limeftune, the fhells 
of marine animals, magnefia alba, &c. in a very large 
proportion, conftituting one-half, and fometimes more, of 
their weight; and that it might always be extracted from 
the atmofphere, in unlimited quantity, by expofmg cer¬ 
tain fubftances to it. This fluid, being found fo mani- 
feftly acid, has now obtained the name of aerial acid. 
Fixed air is the heavieft of all pennanently-elaftic flu¬ 
ids, excepting thofe derived from the mineral acids. Mr. 
Kirwan determines it to be to common air as 1500 to 1000, 
the barometer being at 29-85, the thermometer at fixty- 
four, and the fixed air being extracted from calcareous 
fpar by marine acid, whofe fpecific gravity was 1-0145. 
When combined with calcareous earth, it is prodigioufty 
concentrated; and, were it polfible to exift by itfelf in that 
ftate, it would be the heavieft body known, gold and pla- 
tina excepted. To prove this, Mr. K. firft afeertained 
the fpecific gravity of a piece of white marble; then ex¬ 
pelled the fixed air from a known weight of it finely pow¬ 
dered, by means of diluted vitriolic acid; the bulk and 
weight of the obtained fixed air beingalcertained. Next, 
he calcined a known quantity of the fame fort of marble,, 
by keeping it in a white heat for the fpace of fourteen 
hoursj after which, being weighed again, and from the 
w eight loft by this calcination, the weight of the fixed air, 
which mull have efcaped from it according to the above- 
mentioned experiment, being fubtrafted, the remainder 
is the weight of water contained in the marble; from 
which experiments it appears, that 100 grains of the mar¬ 
ble contained 32-42 grains of fixed air, 11-66 grains of 
water, and 56-92 grains of pure calcareous earth. 
“ I next (fays he) proceeded to difeover the fpecific gra¬ 
vity of the lime. Into a brafsbox, which weighed 607-65 
grains, and in the bottom of which a fmall hole was dril¬ 
led, 1 fluffed as much as poflible of the finely-powdered 
lime, and then ferewed the cover on, and weighed it both 
in air and in water. When immerfed in the latter, acon- 
liderable quantity of common air was expelled ; when this 
ceafed, I weighed it. The refult of this experiment is as 
follows: Grains. 
Weight of the box in air - - 607-65 
Its lofs of weight in water - -. 73*75 
Weight of the box and lime in air - 1043-5 
Weight of the lime fingly in air - 435-85 
Lofs of weight of the box and lime in water 256-5 
Lofs of weight of the lime fingly - 182-3 
“ Hence, dividing the abfolute weight of the lime by its 
lofs in water, its fpecific gravity was found to be 2-3908. 
“ From thefe data I deduced the fpecific gravity of fixed 
air in its fixed ftate; for 100 grains of marble confift of 
55-9.2 of earth, 32-42 of fixed air, and n-66 ot water; 
and the fpecific gravity of the marble is 2-717. Now, 
the fpecific gravity of the fixed air, in its fixed ftate, is as 
its abl’olute weight, divided by its lofs of weight in wa¬ 
ter; 
