phial with the gns, and holding it with its 
mouth downwards, bring the gas into contact 
with the flame of a candle; the air will take 
fire, and burn silently with a blueish flame. 
In a strong phial mix equal parts of hydrogen 
gas and common air, and apply to the mouth 
a lighted candle, and it will burn with a sud- 
den and loud explosion. One part of oxygen 
gas, and two or three of hydrogen gas, will 
give a report equal to that of a pistol. 
Hydrogen gas lias an unpleasant smell ; it 
extinguishes burning bodies ; it is fatal to ani- 
mals ; and is, as we have observed, consider- 
ably lighter than atmospherical air. 
I hese then are the three simple or original 
gases, from which, variously modified, all the 
rest are produced ; and the first of these pro- 
ductions is universally diffused, and of the first 
importance to life, constituting an essential 
part of what we constantly breathe, and by 
which we are surrounded, atmospheric air. 
, Air, combined, or atmospheric gas, is a 
mixture of two or three substances in the 
elastic state. By the powers of chemistry this 
fluid, when examined, is found to consist prin- 
cipally of oxygen air, azote, and carbonic acid, 
in certain proportions. From the abundant 
production of inflammable air, or hydrogen 
gas, at the surface of the earth, in consequence 
of the corruption or decomposition of animal 
and vegetable matters, this fluid must also be 
generated ; yet its extreme levity will natu- 
rally carry it to the higher regions, so that, 
though a part of the atmosphere, it is placed 
in a situation beyond the examination of che- 
mists. 
To a mixture then of oxy gen and azotic air, 
with carbonic acid, the term atmospheric air 
is applied ; and this mixture is in the propor- 
tion of 27 parts of oxygen air, 72 of azotic, 
and 1 of carbonic acid gas. 
The proofs of this composition of atmosphe- 
ric air were first offered by Mr. Scheele, who 
found, on its exposure to certain substances, 
that it suffered a diminution of volume, and 
that by this diminution it was rendered unfit 
for the support of life. This abstracted part, 
therefore, could not fail to be oxygen or vital 
air ; and from this mixture of oxygen and 
azote, he naturally inferred that atmospheric 
air came to be formed. T his he farther con- 
firmed by restoring oxygen to it, in conse- 
quence of which it regained all its properties 
of atmospheric air. On the same subject he 
was succeeded by Lavoisier, who, in addition 
to these facts, showed that the oxygen, or at- 
tracted part, was received by the substance 
producing the change, and could be often re- 
covered again from it. 
But though the composition of atmospheric 
air has been thus ascertained, something still 
remains wanting to complete it ; and this is 
the manner of combining by experiment its 
parts. Hence it is doubted whether its parts 
exist naturally in a state of chemical combi- 
nation, or of mechanical mixture. That the 
latter takes place appears probable from the 
different proportion of oxygen which it is 
found to contain in the higher and lower re- 
gions, it being always greater towards the sur- 
face of the earth ; and from the unlimited 
proportion in which these airs can be mixed, 
while the different matters present in the at- 
mospheric regions may tend strongly to pre- 
vent their separation. At the same time, as a 
proof of its simple mixture, it is soluble in 30 
times its weight of water. 
From this knowledge of the composition of 
atmospheric air, an attempt lias been made 
to ascertain its purity, or its relative capabi- 
lity of supporting animal life in different situa- 
tions. T his is effected by eudiometry, or 
measuring the exact quantity of oxygen the 
air contains. 
To do this it requires to add to the air some 
body capable of combining with its oxygen, 
and from the diminished volume of air, the 
quantity of oxygen is inferred. 
Different substances have been employed 
for this purpose, and each preferred by differ- 
ent chemists. 
The first eudiometer was made in conse- 
quence of Dr. Priestley’s discovery, that when 
nitrous gas is mixed with atmospheric air over 
water, the bulk of the mixture diminishes ra- 
pidly ; in consequence of the combination of 
the gas with the oxygen of the common air, 
and tlie absorption of the nitric acid thus form- 
ed by the water. 
Vv hen nitrous gas is added to nitrogen 
gas, no diminution takes place ; but when it 
is mixed with oxygen gas in proper propor- 
tions, the absorption is complete. Hence it 
is evident, that in all cases of a mixture of 
these two gases, the diminution will be in 
proportion to the quantity of the oxygen. 
Of course, it will indicate the proportion of 
oxygen in atmospheric air, and, by mixing it 
with different proportions of air, it will indi- 
cate the different quantities of oxygen which 
they contain, provided the component parts 
of air are susceptible of variation. 
Dr. Priestley’s method was, to mix toge- 
ther equal quantities of air and nitrous gas in 
a low jar, and then transfer the mixture into 
a narrow graduated glass tube, about three 
feet long, in order to measure the diminution 
of bulk. Ide expressed this diminution by 
the number of hundredth parts of nitrous gas 
and common air: and if the sum total was 200, 
or 2.00 ; suppose the residuum, when mea- 
sured in the graduated tube, to amount to 
104, or 1.04, and of course, that 96 parts of 
the whole hail disappeared, lie denoted the 
purity of the air thus tried by 104. 
Atmospherical air is without taste, and for 
the most part without smell. It is invisible, 
transparent, necessary to the support of com- 
bustion, vegetation, and animal life, particu- 
larly respiration. It is absorbed in a certain 
quantity by water, and again expelled by 
boiling, or by the air-pump removing pres- 
sure. 
Air, alkaline, or ammoniacal gas. This 
air possesses a strong pungent smell, and is 
even capable of inflaming the skin of ani- 
mals. Its lightness is next to that of inflam- 
mable air, and in specific gravity it falls short 
of atmospheric air, in the proportion of 600 
to 1000, and it is incapable of supporting ani- 
mal life, and also combustion, though the flame 
of a candle enlarges before it is extinguish- 
ed by it. It is proved to be a compound of 
azote and hydrogen, 1000 parts of it contain- 
ing 807 of azote, and 193 of hydrogen. This 
air has a strong attraction for water, and is 
rapidly absorbed by it. When dissolved with 
water it produces heat ; and when dissolved 
with ice it produces cold. 
Ammoniacal gas was first discovered by 
Dr. Priestley : it is no where found in a na- 
tural state, but must be produced by an arti- 
ficial process. To obtain it, put into a re- 
tort u certain quantity of liquid ammonia, and 
heal the bottom of the retort, and having suf- 
fered some air to escape from the retort and 
the tube, the gas may be collected in vessels 
filled with mercury. This gas, which seems 
to be nothing but ammonia deprived of wa- 
ter, is perfectly absorbable by water, and the 
solution forms liquid ammonia (the same 
which is vulgarly called sal volatile and spirit 
of hartshorn). It is the lightest of all the 
saline gases, has a penetrating odour, and 
gives a strong tint of green to blue vegetable 
colours. It combines rapidly with carbonic, 
muriatic, and sulphureous acid gases, and 
forms neutral salts, throwing out a great deal 
of heat, which arises from the free state of 
the caloric that had been combined with 
these gases. 
Ammoniacal gas suffocates animals, and ex- 
tinguishes burning bodies ; but it is so far in- 
flammable, that it increases the flame of a 
taper before it extinguishes it. 
Carbonic acid gas is the first elastic aeri- 
form fluid, different from common air, that 
was known. We are indebted to Dr. Black, 
of Edinburgh, for a knowledge of some of 
its most remarkable properties. In the year 
1755 he discovered the affinity between it 
and the alkali's ; and Bergman, in 1772, proved 
that it was an acid. 
Carbonic acid gas cannot support flame, 
nor animal life ; its taste is acid. Neither 
light nor caloric seem to produce any effect 
upon it, except that the latter dilates it. it 
is absorbed by water. These two fluids, after 
considerable agitation, at last unite, and form 
an acid fluid. I he colder the water, and the 
greater the pressure applied, the more car- 
bonic gas it will absorb. Water, so impreg- 
nated, sparkles upon agitation ; it lias an aci- 
dulous taste, and reddens tincture of litmus. 
Heat disengages the gas from the water. 
Carbonic acid gas precipitates lime from its 
solution in water. It is eagerly attracted by' 
the alkalis. Its specific weight is to that of 
atmospheric air, as 1500 to 1000. It may be 
poured from one vessel into another. 
Of all the bases of the gases, that of car- 
bonic acid gas is diffused in the greatest 
abundance throughout nature. It is found in 
the state of gas, and also in combination with 
a great variety of bodies. 
It may be easily obtained as follows : Put into 
a common retort a little marble, chalk, orlime- 
stone, and pour on it sulphuric acid, diluted 
with about six times its weight of water ; an 
effervescence will ensue, and carbonic gas 
will be disengaged, which may be collected 
over mercury; but a mercurial apparatus is 
not absolutely necessary, since the gas may 
be collected over water, if it is to be used 
immediately. 
Marble, lime-stone, and chalk, consist ofthis 
matter and lime. On presenting to it sul- 
phuric add, a decomposition takes place ; the 
sulphuric acid having a greater affinity to the 
lime than the carbonic acid has. It therefore 
unites to it, and forms sulphate of lime, dis- 
engaging, at the same time, the carbonic acid 
in the state of gas. 
Carbonic acid gas is often found in the 
lower parts of mines, caverns, tombs, and 
such other subterraneous places as contain 
materials for producing it : it is then called the 
choke-damp. The grotto Del Cane, near 
Naples, has long been famous for the quan- 
tity of this gas produced there, which is so 
great, that it runs out at the opening like a 
