AERO 
id from the burning fubftances; thus gunpowder gene¬ 
rates a great quantity of elaftic fluid when inflamed, &c. 
Even the eleftric fpark feparates fixed air from com¬ 
mon atmofpherical air; for when a number of thefe fparks 
are taken in a fmall quantity of common air over lime- 
water, a diminution will take place, the lime will be pre¬ 
cipitated, and, if we put a blue vegetable juice inftead of 
the lime-water, it will be turned red by the acidity of the 
fixed air depofited upon it. 
The calcination of metals, as already obferved, phlo- 
gifticates, and confequently diminifhes, common air; but 
does not produce any fixed air, fince the lime-water, over 
which the calcination is made, does not become turbid ; 
and, when metallic calces are expofed to a fufficient heat, 
they generally yield fome fixed air: fo that it feems the 
fixed air which is formed in the aCt of the calcination of 
metals is abforbed by the calx. Some fixed air may be 
obtained from red lead, by no greater degree of heat than 
that of the flame of a candle applied to the vial that holds it. 
The calcareous earths, when added upon by acids, yield 
a vaft quantity of fixed air. Dr. Prieftley, in his experi¬ 
ments on the production of dephlogifticated air from vari¬ 
ous fubftances, when moiftened with nitrous acid, and af¬ 
terwards expofed to a fufficient degree of heat, generally 
found that fome fixed air was produced together with tire 
dephlogifticated air; but often obtained fixed air only, 
without any dephlogifticated air being mixed with it, or 
fixed and nitrous air together. But in thofe experiments 
he moftly ufed a gurr-barrel, fo that, as he juftly obferves, 
the iron might have contributed to the formation of the 
fixed air. In fa 61 , when he tried fubftances of the fame 
fort, firft in a gun-barrel and then in glafs vefl'els, he ob¬ 
tained more fixed air in the former than in the latter cafe. ! 
Moft minerals contain fixed air, which may be extracted 
to a certain degree by means of heat. Mr. Krenger, from 
a greenilh fufible fpar, which was ’luminous in the dark, 
obtained a permanently-elaftic fluid, which, like fixed air, 
cryftallized a folution of fixed alkali. The malachite alfo 
contains a vaft quantity of fixed air, as pure as that ex¬ 
tracted from chalk by vitriolic acid. From almoft every 
metallic ore and earthy mineral fome fixed air may be ob¬ 
tained, as well from chalk, lime-done, marble, marine- 
fhells, fixed and volatile alkali, and from magnefia, by 
means of a violent fire, or of acids. 
By acids. Calcareous fubftances produce abundance of 
fixed air, efpecially when aCted upon by any of the ftrong- 
er acids, fuch as the vitriolic, which is both the cheapeft 
and fitteft for the purpofe. The phenomena attending 
the production of fixed air from calcareous fubftances, See. 
are the following: — i. When mixed with acids, they ef- 
Yervefce; and produce a permanently-elaftic fluid, name¬ 
ly, fixed air. 2. They retain the fixed air very obftinate- 
ly; fo that a ftrong fire is neceffary to expel it from mag¬ 
nefia, and the ftrongeft is not fufficient to expel it entirely, 
either from fixed alkalies or calcareous earths. When 
thefe fubftances are treated with acids, they yield their 
fixed air, becaufe they have a ftronger attraction to thofe 
acids than to the fixed air. 3. Calcareous earths, which 
are infoluble in water, when deprived of the fixed air be¬ 
come foluble in it. Thus lime-ftone is not, but lime (viz. 
lime-ftone deprived of its fixed air) is, foluble in water. 
And, if fubftances deprived of their fixed air are put in a 
fituation to recover it, they again become infolublein water. 
4. Alkalies, both fixed and volatile, when deprived of 
their fixed air, become more cauftic, and more powerful 
folvents, incapable of cryftallization, and of eftervefeing 
with acids. But if to thofe alkalies, and alfo earths ren¬ 
dered more cauftic, their fixed air be reftored, they ac¬ 
quire at once all the properties they had before, viz. they 
become more mild, eft’ervefee with acids, recover thejr 
weight, &c. Dr. Black, to whofe accurate and fatisfac- 
tory experiments on this fubjeCt chemiftry is greatly in¬ 
debted, gives the epithet of mild to thofe fubftances when 
combined with fixed air, and of cauftic when deprived of 
it; as cauftic calcareous earth, cauftic fixed alkali, &c. 
Vol. 1 . No. 11. 
LOGY. »dt 
Eafy Methods of obtaining Fixable Air for occafional Expert . 
merits, &c. 
By fermentation. Mix together equal parts of brown 
fugar and good yeaft of beer, to which add about twice 
the bulk of water. This mixture being put into a vial, 
to which a bent tube with a cork may be adapted, will 
yield a confiderable quantity of fixed air, which may be 
received into a vial filled with quickfilver or water, as in 
the following procefs. 
By acids. Let a glafs tube be bent, and fix a cork to 
one of its extremities, fo as to fit the neck of a common 
vial. Fill a fimilar vial, or any glafs receiver, with wa- 
ter, and invert it in a bafon about half filled with water. 
Next put fome chalk or marble, grofsly powdered, into 
the bottle, fo as to fill about a fourth of it, and add wa¬ 
ter enough to cover the chalk; then pour in as much vi¬ 
triolic acid as will make about one-fifth of the whole flu¬ 
id. Apply immediately the cork, with the tube, to the 
bottle, and let the extremity of the tube pafs through the 
water of the bafon into the neck of the bottle, which mull: 
be kept up with the hand, or other convenient fupport, as 
it cannot reft upon the bottom of the bafon. The mixture 
in the bottle will immediately begin to effervefee and grow 
hot, and the fixed air will be copioull.y emitted, and paf- 
fing through the bent tube, and afterwards through the 
water, will afeend to the top of the inverted bottle. In 
proportion as the elaftic fluid collefls, the water will gra¬ 
dually defeend, and at laft be quite expelled, and the bot¬ 
tle thus filled with fixed air may be corked under water, 
and kept for life. That fixed air will extinguifh flame 
may be ea/ily proved by palling a lighted taper into any 
open jar in which it is contained ; and that it is very freely 
abforbed by water will appear on tailing that through 
which the bubbles have arifen in the above procefs. The 
flavour will be brifk and agreeably acidulous. In this 
ftate, too, it changes the blue infufion of fome vegetable 
fubftances into red; fo that, if a weak folution of helio¬ 
trope be mixed with it, the liquor acquires a reddifh ap¬ 
pearance. It alfo corrodes iron, and fome other metals, 
much more eafily than common water. But the greateft 
and moftufeful property of this acidulated water, or wa¬ 
ter impregnated with fixed air, is its being a powerful an- 
tifeptic. As moft of the mineral waters are medicinal 
principally on account of their being thus impregnated, 
and alfo containing fome fmall portion of metal or fait 
diflolved ; they may be imitated by impregnating common 
water with fixed air, and then adding that quantity of fait 
or of metal, that, by analyfis, the original mineral waters- 
are found to contain. For thefe purpofes, indeed, a well- 
contrived glafs apparatus is fold in the (hops. 
Fixed air has long been conftdered a very powerful re¬ 
medy in putrid diffiafes. Sir John Pringle and Dr. Mac- 
bride have fhewn experimentally, that fixed air is dif- 
charged by fuch fubftances as form our common food ; 
and both aferibe the prefervation of the body from pu¬ 
trefaction in a great meafure to the fixed air, which in 
digeftion is difengaged from the aliment, and incorporates- 
with the fluids of the body. 
The fame property alfo renders it ufeful for feveral 
oeconomical purpofes. Mr. Henry found, that fixed air 
can preferve fruit fora confiderable time; and Dr. Mac- 
bride obferves, that not only good meat was preferved in¬ 
corrupt for a confiderable time, when expofed to fixed air, 
but that the putrefadlion of fubftances actually putrid was 
impeded by this means; and even that thofe fubftances 
were reftored from the putrefeent to the found ftate. 
Milk acquires an acidulous tafte by being impregnated 
with fixed air, and is thereby preferved for fome days; 
which affords a very eafy expedient of preferving milk in 
thofe places where it cannot be had new very often. 
To produce Infiammabk Air. The procefs for making this 
fort of gas may be conducted in the fame way as for fixed 
air, only fubftituting for the chalk about the fame pro¬ 
portion of iron-filings or grofsly-powdered zinc. If the 
T t capacity 
