CHEMISTRY. 195 
jrtg water alfo. Expofe it to thecontad of the fun's rays, 
and v,ery pure oxygen gas will be produced. The emifiion 
of vital air is in proportion to the ftrength of the plant, 
and the brightnefs of the light; but a direct emifiion ot 
the rays of the fun is not neceffary to the production of 
this gas; it is fufficient that it is placed in a good light, 
for it to refpire oxygen gas. The general properties of 
this gas are—It is heavier than atmol'pherical air; it is 
the only air proper for refpiration, as is proved by expe¬ 
riment. Fill a tube with oxygen gas, and put therein a 
lighted taper; the flame will fpread at the inftant of im- 
merfion, and it will burn with fuch brightnefs as the eye 
can hardly endure ; a ftrong and adive heat is alio pro¬ 
duced under tliefe circumftances. The fame efleds will 
be produced if a lighted coal be introduced into the tube ; 
or, if bits of wood, lighted and extinguifhed, be plung¬ 
ed fuddenly into the jar, they will flame again. 
The lovers of chemiftry have endeavoured to exhibit 
this experiment in different ways ; we are indebted to In- 
genhouz for having prefented it in a manner at once link¬ 
ing and agreeable: take a very fmall piece of very thin iron 
wire twilled fpirally; flick one end of it into a cork intended 
to flop the bottle to be made ufe of; fallen to the other 
end of the wire a little bit of tinder. Then fill the bottle 
with oxygen gas ; light the tinder, and introduce it into 
the bottle with the wire, which, having the cork with it, 
prefently clofes the bottle. As foon as the tinder gets 
within the oxygen gas, it begins to burn very blight; it 
communicates inflammation to the iron, which burns 
and throws out bright fparks, that fall to the bottom of 
the bottles in round globules, which become black as 
they get cool. The iron thus burnt is more brittle than 
glafs itfelf; it falls entirely to powder. When a lighted 
taper or other body is plunged into a tube filled with 
oxygen gas, a fubilance is brought into contad with it, 
which has more affinity with the bale of this gas, than 
that bale has with caloric. Lavoifier and Erhman expol'- 
ed almoll all known bodies to the adion of fire, alimen- 
tated by oxygen gas only; and obtained effeds from them 
which even the burning lens could not produce. For this 
purpofe, a bladder is filled with this gas ; and it is di¬ 
rected, by means of a metal or glafs tube, againll a light¬ 
ed coal which had been previoully hollowed that it might 
contain the fubilance to be wrought upon. 
Oxygen gas is more falubrious than atmofplierical air. 
Take two birds of the fame kind, and of the fame degree 
of ftrength; place one of them under a jar containing 
two meafures of oxygen gas ; put the other at the lame 
time under another jar, full of atmofpherical air, of the 
Fame capacity as the firll: it will be found, that the bird 
placed under the jar filled with oxygen gas will live about 
three quarters of an hour, and after it is taken away the 
air will Hill be fufficiently pure ; but the bird confined 
in common air dies in a quarter of an hour, and the air 
will be found quite contaminated, and unfit for re¬ 
fpiration. 
We lhall not now examine the various opinions rela¬ 
tive to the nature of this gas. Modern chemills fuppol'e 
every aeriform fluid to be compofed of a bafe , and of ca¬ 
loric. The bafe then is what ought to draw our atten¬ 
tion at prefent. Every combullible matter may ferve as 
a means to come at this knowledge; but we lhall prefer 
phofphorus, which more particularly polfelTes the pro¬ 
perty of extracting from caloric whatever fubilance is 
united with it, in order to form oxygen gas. For this 
experiment, take a bell-glafs or jar of about 350 cubic 
inches capacity, and fill it with oxygen gas over water 3 
place it over the mercury bath by means of a Aider; then 
place under the jar a cafe containing pholphorus; raile 
the mercury in the jar to a certain height by means of 
a glais lyphon palled under the jar; that this may not fill 
In pafl'mg through the mercury, twill a bit of paper at 
its extremity; then, with a piece of bent red-hot iron, 
light the pholphorus. The combultion of the pholpho¬ 
rus is very 1 rapid, accompanied with a large flame and 
great heat. In the firll moment of combullion, the oxy¬ 
gen gas is confiderably dilated by the heat; but, foon 
after the mercury riles above its level, and there is a con- 
fiderable ablorption; as the combullion proceeds, the in- 
fide of the jar is covered with light fnowy flakes, which 
are nothing but concrete phofphoric acid. 
For Seguin’s experiment, pafs a little phofphorus un¬ 
der a jar filled with mercury ; the phofphorus, being 
lighter than the mercury, riles to the top of the jar; it 
is heated, by palling a burning coal round the jar. When 
the phofphorus is melted, put in the oxygen gas. A ra¬ 
pid inflammation takes place; and, it the gas be very 
pure, there is no refidue, and the mercury riles to (die 
top of the jar. This is a good procefs to try the purity 
of air; and Seguin calls it the eudiometer. If the expe¬ 
riment be made with impure oxygen gas, or mixed with 
azotic gas or any other elaltic fluid nof favoui able to 
combultion, the mercury will not rife to the top of the 
jar; there will be a refiduum. What has been faid of 
phofphorus may be faid equally of fulphur, carbon, &c. 
The greater part of combullible bodies which are burnt 
in oxygen gas is always converted into acid. In fliort, 
oxygen gas has confiderable lhare in all the great pheno¬ 
mena of nature, fuch as combullion, refpiration, and ve¬ 
getation. It is the only air proper for combultion. 
Of COMBUSTION. 
It is very difficult to define combullion : it is an aggre¬ 
gate of effects produced by combullible matters, heated 
with the concurrence of air, and whofe principles are 
heat, motion, flame, rednefs, and a change in the burnt 
matter. 1. In all combullion, there is an abforption of 
the bale of oxygen gas; of which the experiment with 
phofphorus affords an evident proof. In the oxydation 
of metals by acids, in the reduction of metallic oxyds 
by carbon, in the combullion of fulphur, phofphorus, 
carbon, &c. by nitric acid; in all thefe cales certainly 
there is no oxygen gas ; but concrete oxygen exills ill 
one of the bodies compoling the mixture; and it is on 
the paflage of the oxygen more orlefs folid from the body 
which contains it into that which is dellitute of it, that 
combultion depends. 
a. The refiduum of the combullion is always heavier 
than the body was previous to its being burnt. Metals 
in general acquire greater weight when combined with 
oxygen ; xoo parts of lead yield by combultion no parts 
of oxyd ; fuipliur yields more fulphuric acid in weight, 
after combultion, than it weighed of itfelf. It has been 
erroneoully faid, that there exilled fubltances, fuch as 
oils, alcohol, wood, and ether, which loll a confide;able 
part of their weight by combultion. It is certain that 
combullible bodies, whofe inflammable parts are volatile, 
prefent to our fienfes much lefs of their weight by cOmbuf- 
tion; but this lofs only takes place in appearance: it is 
eafy to be fatisfied of this, if we conlider, that what re¬ 
mains fixed after combullion, is not the only refidue of 
the combullible body; and that all thofe which are vo¬ 
latile, change by combultion into aeriform fluids which- 
dilfipate, and are not feen. Ether and alcohol are ex¬ 
amples of this truth. 
3. The increale of weight acquired by the burnt body 
is equal to the weight of the ablorbed oxygen gas. When 
the refidue of the combullion is fixed, this is eafily afcer- 
tained. Lavoifier has demonllrated, by accurate experi¬ 
ment, that, if calcination or oxydation of metals be made, 
either under beli-giafl'es, or in doled vefiels, with known 
quantities of air, the oxygenated part of the atmofphe¬ 
rical air is abl'orbtd during the oxydation, and that 
oxyded metal gains as much in weight as the atmolpheric 
ail lofes by the oxydation of the metal. 
4. In all combui.ion, there is a dilengagement of ca¬ 
loric and light. When combultion is made by the con- 
tad of air, the body which burns has more affinity, or 
elective attmdion, towards the bafe of the oxygen gas, 
than that bafe has with the caloric. Jn conlequence of 
this 
