C HEMISTRY. 
198 
Sulphure of potafu has alfo the property of decompofmg 
atmofpherical air. Put two or three bits of fulphure, 
as big as a pea, into a retort, which fill with water, 
taking care to (lope it fo as to let all the air which might 
be m the globular part pafs into the neck ; flop the ori¬ 
fice with your finger, and put its neck downwards into 
the pneumatic cittern, to let in the gas for trial in the 
ordinary way. By inclining it again, with care, different 
ways, all the water will be difplaced, and the fulphure 
remain in the bulb. This done place the retort in a ver¬ 
tical pofition, infert the end of it into a glafs tube under 
water, and put a fmall lighted taper under the bulb. 
The firft impreffion of the heat dilates the gafeous fluid ; 
and, as the fulphure begins to bubble up, the Water riles 
rapidly; and if the air is pure, there is a total abforp- 
tion; if it be common air, only a certain quantity of 
water rifes into the retort, which reprefents exadtly the 
volume abforbed. Upon this experiment is founded the 
Utility of Guyton’s eudiometer. 
If chopped vegetables, flowers, or fruit, be placed un¬ 
der jars filled with atmofpherical air, they confume the 
oxygen, and there remains an elaftic fluid improper for 
combuftion or refpiration. The fame refult takes place 
with phofphorus, fulphure of potafh, &c. That refpi¬ 
ration, as well as combuftion, decompofes common air, 
the following experiments will prove: 1. Pafs the gas 
which comes from the lungs through lime-water, and a 
precipitation takes place. 2. Draw the fame gas through 
tinfture of turnfole, it will turn red; if pure alkali be 
fubftituted for the tinfture of turnfole, it becomes effer- 
vefcent. All thefe differences prove, then, that air is 
decompofed, fince, on the one hand, a gas improper to 
combuftion is produced ; on the other, a'fixation of oxy¬ 
gen gas in the bodies brought into contaft with com¬ 
mon air; and, laftly, by the afl of refpiration, a pecu¬ 
liar gas is produced, which forms frelh combinations. 
Atmofpherical air is compofed of tweniy-feven parts of 
oxygen gas, and about feventy-two of azotic gas. 
Of combustible bodies. 
Azotic gas. —This elaftic fluid, which forms more 
than two-thirds of the air of the atmofphere, was at firft 
called mephitis by Lavoifier, becaufe it extinguilhes bo¬ 
dies in combuftion, and deftroys animal life; but as all 
the gafes, except vital and atmofpherical air, are equally 
noxious, and as the name of mephitis is a general ex- 
preftion which belongs to them all alike, and has always 
been given to elaftic fluids, which are not refpirable,. the 
name of azotic gas, is now given to this aeriform fluid; 
and this denomination admits the name azot, as the 
fubftantive, to the bafe of this gas, which, like that of 
vital air, or oxygen, becomes fixed by combining with 
various lubftances. To give in this place foine informa¬ 
tion refpeffing the nature of this azotic gas, we (hall 
defcribe iome of its properties. It is fomewhat lighter 
than atmofpheric air, and occupies the upper part of 
rooms in which the air is altered by refpiration and 
combuftion. Though it is very noxious to animals in 
its ftatq of elaftic fluidity, yet its bafe, or azot, is one of 
the component parts of their bodies, from which it is 
obtained in very great quantities. It is one of the con- 
ftituent parts of volatile alkali, or ammoniac, and of the 
nitric acid. It is abforbed by vegetables, and perhaps 
by animals. It is likewife very probable that it forms 
one of the principles of all the alkalis, and that it may 
be confidered as the true alkaligen, oppoled to the bale 
of vital air or oxygen. The atmofphere would be then, 
according to thefe confiderations, an immenfe refervoir 
of the acidifying and alkalifying principles, without be¬ 
ing itfelf either acid or alkaline. 
There are feveral modes of obtaining azotic gas. 1. By 
fulphure of potalh expofed under a bell-glafs in a quan¬ 
tity of atmoipherical air. 2. By Bertholiet’s method of 
treating mufcular flefli, or the fibrous parts of blood well 
walhed in weak nitric acid. For this purpofe, cut the 
3 
flelh in pieces; put it either into a retort, or into a phial 
or matrafs; pour thereon weak nitric acid; adapt a tube 
to the retort or phial, and lute it; place the apparatus- 
over a fand-bath, and pafs the tube under a jar in the 
mercurial pneumatic apparatus : the water ciftern may 
ferve alfo when the experiments are not required to be 
very exact. 3. Fourcroy oblerved, that the air-bladders 
of the calk contained azotic gas. To obtain it, nothing 
more is neceffary than to bruife them in jars filled with 
water. 4. It may be obtained by expofing a mixture of 
iron and fulphur beat up in water, over mercury, in at¬ 
mofpherical air. 5. By the oxydation of metals, the ran¬ 
cidity of oils, the combuftion of phofphorus, &c. 6. By 
the decompolition of animal and vegetable lubftances, 
the leaves of plants, See. All thefe fubftances decompofe 
atmoipherical air;,and the relidue is azotic gas. 
Its properties. —This gas is deftruftive of combuftion 
and refpiration : it is ealy to prove this by plunging a 
lighted taper into a cylindrical tube filled with this gas; 
the light goes fuddenly out; and animals die in it. This 
gas is not acid : if it be put in contadl with water, lime- 
water, and tindiure of turnfole, the nature of thefe bo¬ 
dies is not changed; the azotic gas ftill remains pure. 
By mixing azotic gas and oxygen gas, a re-compofition 
of atmofpherical air is produced. Put under a bell-glafs 
filled with water, three parts of azotic gas and one of 
oxygen gas ; in the fluid which is the refult of this ex¬ 
periment, put a light, and it will burn as in atmofpheri¬ 
cal air. The bafe of azotic gas is not fufficiently known. 
Hydrogen gas. —This is always belt obtained by a 
decompofition of water: for this purpofe-pafs a gun-bar¬ 
rel through a furnace, obferving to Hope it towards the 
narrow-eft end. In the upper extremity infert a bent 
tube, as (hewn at A, fig. 12, in the engraving; while the 
other extremity is terminated by a tube, B, which is 
palled into the pneumatic ciftern, under a jar. The ap¬ 
paratus being thus difpofed and well luted, make the 
gun-barrel red-hot: when the barrel begins to be very 
hot, put water, drop by drop, into the tube A : the wa¬ 
ter will run through; and, as foon as it comes in con¬ 
tact with the gun-barrel, it is decompofed ; the iron takes 
up the oxygen, and the hydrogen is difengaged in a gafe¬ 
ous ftate through the tube B. 
This gas is obtained alfo by pouring fulphuric acid 
upon iron-filings or zink. Take an apothecary’s phial, 
or a fmall matrafs containing iron-filings or zink ; pour 
over it weak fulphuric acid, whole fpecific weight to 
that of water (hall be only as eleven to ten ; adapt there¬ 
to a bent tube, which is to be palled under a bell-glafs. 
As foon as the fulphuric acid is in contadl with the iron, 
it excites a brilk effervefcence; the water which ferves 
as a vehicle to this acid is decompofed, the oxygen ftrikes. 
upon the metal, and the hydrogen is difengaged. Till j 
gas is likewdfe furniflied by the Ample diftiliation of ve¬ 
getable fubftances, animal putrefcence, and vegetable 
fermentation. 
Its properties,— It has a difagreeable fmell; is invifible, 
elaftic, and twelve times lighter than atmofpherical air; 
on the lightnefs of hydrogen gas, or inflammable air, 
depends the theory of the air-balloon. This gas is not 
proper for maintaining combuftion, as will appear from, 
the following experiment: Having introduced hydrogen 
gas into a bell-glafs filled with mercury, put in a fmall 
laucer with I'ome tinder and a little phofphorus; touch 
the phofphorus with a red-hot bent iron-wire thruft 
through the mercury, and the phofphorus melts imme¬ 
diately, but there is no flame. 
Hydrogen gas and atmospherical air. —Fill a 
bell-glafs with hydrogen gas, draw it out of the pneu¬ 
matic ciftern, and put to it immediately a lighted taper; 
the gas lights, and the flame is feen fucceffively to de- 
feend in the bottle. There are feveral other ways of 
producing this effedt. Put iron-filings into a bottle with 
two necks, as reprefented at fig. 13, in the plate. To one 
of the oecks adjuft a tube of glafs terminated by a capil- 
