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A 1 R 
Priestley, in which it was found, that on in- 
flaming a mixture of common and inflam- 
mable air by the electric spark, a loss of 
weight always ensued, and that the inside of 
the vessel in which it was fired became always 
moist or dewy, though ever so carefully dried 
before. On repeating the experiment, Mr. 
Cavendish did not perceive the diminution of 
weight which Mr Warltire supposed to take 
place, but the latter effect was completely 
exemplified. In prosecuting the experiment, 
it appeared that it was only the pure or em- 
pyreal part, that is, about one-fourth, of the 
common air which was consumed, and the 
water produced was perfectly tasteless and 
pure ; on mixing vital with inllammable air in 
a due proportion, and passing through them 
an electric spark, the whole portion lost its 
■elasticity, and was condensed into water. 
Mr. Cavendish pursued his experiments 
with remarkable success, to ascertain the 
constituent principles of what was then called 
phlogisticated air, or that which constitutes 
the impure and unrespirable portion of the 
atmospheric air; and by passing the electric 
spark through common air, and through a 
Certain mixture of vital and phlogisticated 
airs, he was able totally to condense the lat- 
ter, and to ascertain its constituent principle 
to be the same with that of nitrous acid, with 
(as he then thought) a small portion of in- 
flammable matter. In this latter opinion, 
however, he has since been corrected bv La- 
voisier, and other modern chemists, who have 
proved that azotic, or phlogisticated air (as 
it is called by the English chemists) is no 
other than the basis of the nitrous acid. 
In Mr. Cavendish’s experiment, as he pro- 
bably used air which had been rendered im- 
pure by combustion, some small portion of 
charcoal, or other inllammable matter, might 
be contained in the air. 
Some gases exi-t in nature without the aid 
of ait, and may be collected ; others are only 
producible by artificial means. The prin- 
cipal airs, or gases, noticed in modern philo- 
sophy are, 
• Oxygen gas or air. Phpsporated hydro- 
Nitrogen gas or air. gen gas. 
Hydrogen gas or Nitrous gas or air. 
air. Sulphureous acid gas. 
Annnoniacal gas or Gaseous oxyd of 
t air- azote. 
Carbonic acid gas. Muriatic acid gas. 
Carbonated hydro-. Oxygenated muriatic 
gen gas. acid gas. 
Sulphuratedhydro- Fluoric acid gas. 
gen gas. 
_ Air vital, or Oxygen gas, formerly termed 
also dephlogistieated and empyreal air: is a 
substanc e destitute both of taste and smell, 
but possessing in an eminent degree the 
power of increasing and supporting animal 
me and. combustion. It is heavier at the 
same time than atmospheric air, in the pro- 
portion of 103 to 100, and the latter, main- 
tains life only in consequence of the quantity 
oi this fluid it contains. This proportion is 
rated at 27 in 100. 
I his air changes the colour of animal and 
vegetable substances. Ir is a composition of 
oxygen and caloric. Combustion by it is 
rendered amazingly intense ; and its powers, 
when urged by the' blowpipe, tar exceed the 
powers of any burning lens. 
A lighted wax taper, fixed do an iron wire, 
and let down into a vessel of this gas, burns 
with an inconceivable brilliancy. If the taper 
is blown out, and let down into a vessel of the 
gas, while the snuff remains red-hot, it in- 
stantly re-k indies. A red-hot piece of char- 
coal immersed in this gas, throws out beau- 
tiful sparks. In this gas thin iron wire will 
burn with beautiful effect. During every 
combustion in oxygen gas, the gas suffers a 
material diminution ; and all bodies by com- 
bustion in it acquire an addition to their 
weight. 
Cxygen, or the basis of oxygen gas, is na- 
turally or artificially combined with a great 
variety of substances. From some of these 
it may be detached by the simple application 
of heat, since it has a remarkable attrac- 
tion tor caloric, or the matter of fire, with 
which, when it unites, it becomes expanded, 
and assumes the form of gas or air. 
i he substances from which it may be most 
easily extracted, by means of heat, are red 
lead, calcined mercury, nitre, and manga- 
nese. Dr. Priestley exposed a quantity of 
red lead in tire focus ot a burning glass twelve 
• inches in diameter. A quantity of fixed 
; air, or carbonic acid gas, as it is now called, 
j was always produced at first ; but after that 
was separated, the remainder was found to 
support flame, and to sustain animal life, much 
more vigorously than common air, and to 
have all the characters of dephlogistieated air, 
°r oxygen gas. 
By various succeeding experiments of Dr. 
Priestley and others, it however appears, that 
dephlogistieated or oxygen air, may be ob- 
tained not only by means of heat, but also by 
the action ot the vitriolic and nitrous acids 
upon a number of mineral and metallic sub- 
stances. 
1 his kind of air may also be obtained by 
the same process, from the native oxid, or 
calx of manganese, or from minium or red 
lead, which, it is well known, is an oxid of 
lead, or lead united with oxygen. 
I he better do understand these effects, it 
must be observed, that this fluid is not found 
in these substances in an entire state ; they 
only contain the basis ot it, which is the oxy- 
gen ; for metals neither calcine nor burn, but 
in consequence of their combination with 
oxygen, which by that means becomes solid, 
and joins its weight with theirs. This oxygen, 
is then expelled by the application of heat or 
caloric, which, combining with it, causes it to 
pass into the state of an elastic fluid ; during 
this process, the metal, losing the oxygen 
which had reduced it to the state of an oxid 
or calx, assumes its metallic properties; and 
loses the weight which it had acquired in be- 
coming oxidated. 
I here is, however, a method by which ox- 
ygen gas may be obtained with less heat and 
greater facility, and it is as follows: put some 
red lead into a bottle, togetherwith some good 
strong oil of vitriol, but without anv water. 
Let the red lead fill about a quarter of the 
bottle, and the vitriolic acid be about the 
same quantity, or very little less ; then apply 
a bent tube to the bottle, by inserting it 
through a cork, and having inverted another 
boftlc filled with water in a bason about half- 
filled also with water, direct the other end of 
the crooked tube into the bottle inverted in 
the water. In this stage of the process we 
must observe, that without heat this mixture 
of red lead and vitriolic acid will not afford 
any oxygen air, or a very inconsiderable 
quantity ; it is necessary, therefore, to apply 
the flame of a candle or wax taper to the 
bottle containing the ingredients, while the 
crooked tube opens a communication between 
this bottle and that inverted in the water. In 
this manner the red lead will yields a quan- 
tity of elastic fluid, which will pass through 
the crooked tube into the inverted bottle, and 
as the quantity of oxygen air increases in the 
inverted bottle, the water in it will be seen 
to subside ; this air will not be all pure, be- 
cause a considerable quantity of fixed air en- 
ters with it. In order to separate the' fixed 
from the pure air, the inverted bottle, when 
filled with the compound of both, must be 
agitated in a bason of lime-water, by which 
means the lime-water will absorb the whole 
quantity of fixed air, and leave t he dephlogis- 
ticated air or oxygen gas by itself. 
Oxygen gas may also be obtained in consi- 
derable quantities from the decomposition of 
water, especially from pump water, which, 
when exposed to the sun, emits air slowly ; 
but after it has remained so for a considerable 
time, a green matter adheres to the bottom 
and sides of the glass vessel in whit h it re- 
mained ; afterwards it emits pure oxygen air 
m great quantities, and continues to do so for a 
long time after the green matter has exhibit- 
ed symptoms of decay by turning yellow. 
Dr. Ingenhousz rightly supposed' this green 
matter to belong to the vegetable kingdom, 
and procured pure air by putting the leaves 
of plants into water, and exposing" them to the 
sun. He observes that of land vegetables 
the fittest for this purpose are the poisonous 
plants, such as hyoscyamus, lauro-cerasus, 
nightshade, See. But he extracted the purest 
air from some aquatic vegetables, and from 
turpentine trees, but especially from the 
green matter he collected from a stone trough, 
which had been kept filled with water from a 
spring near the high road. 
M bile Dr. Priestley was engaged in a se- 
ries of .experiments to enable him to purify 
contaminated air, he discovered that vege- 
tables answered this purpose most effectually. 
The experiment by which he illustrates His 
assertion was this : having rendered a quan- 
tity of air very noxious, by mice breathing 
and dying in It, he divided it into two re- 
ceivers inverted in water, introducing a sprig 
of mint into one of them, and keeping the 
other receiver with the contaminated air in it 
alone. lie found, about eight or nine days 
after, the air of the receiver, into which he 
had introduced the sprig of mint, had become 
respirable ; for a mouse lived very well in this, 
but died immediately upon being introduced 
into the other receiver, containing the conta- 
minated air alone. 
It has since been observed, that several ani- 
mal substances, as well as vegetables, have a 
power of separating dephlogistieated air, or 
oxygen gas, from water when exposed to the 
action of the sun fora considerable time. 
d he ingenious count Romford observed, 
that raw silk has a remarkable power of pro- 
ducing pur# air. lie found, that by introduc- 
ing thirty grains of this substance, first washed 
in water, into a thin glass globe four inches 
and a half in diameter, having a cylindrical 
neck three-fourths of an inch wide and twelve 
inches long, inverting the globe into ajar filled 
with the same kind of water, and exposing it 
to the action of the sun in the window, in less 
