COMBUSTION. 
liar element Called caloric. According to 
those philosophers who assert tlie existence 
of this last piinciple, the combination of 
oxygen and the combustible body does 
emit or give out caloric, either because there 
is less room for it in the new compound, 
of which tlie capacity is changed, according 
to Dr. Irvine’s doctrine ; or because a por- 
tion of caloric, which was before latent or 
combined in one or both of the component 
parts, is, according to Black, given out in 
consequence of the resulting attraction of 
the new compound for it being less tlian 
before. They who are disposed to see this 
subject treated at length, may consult the 
system of the ingenious Fourcroy, where 
they will find the modern caloric affording 
the same general services to chemical hypo- 
thesis as were formerly obtained from its 
predecessor phlogiston. 
Notwithstanding the truly valuable and 
numerous discoveries of facts by Black, 
Irvine, Crawford, and other modern philo- 
sophers, we are far from being in possession 
of proof that elevation of temperature is 
universally occasioned by diminution of ca- 
pacity, or the extrication of latent heat. 
But, as we are upon the whole more habi- 
tuated to consider bodies themselves, than 
their properties in the abstract, a prefer- 
ence has been given to the method, of as- 
cribing events to peculiar additional sub- 
stances, rather than to motions or modifica- 
tions of the bodies in which they may take 
place. Many eminent philosophers have, 
nevertheless, considered heat as a motion 
in the particles themselves ; but it is not so 
easy to speculate upon the principles of 
motion among a system of particles, as it is 
to assert the combination and disengage- 
ment of a chemical element, though tliis 
assertion does not remove the difficulty, 
but only places it a step farther off. 
If we admit that the particles of a body 
do not touch each other ; as appears to be 
established from the different degrees of 
inertia and of weight, as well as from the 
expansions and contractions occasioned by 
change of temperature, and other causes ; 
and if we likewise consider the particles as 
attracting each other, — it appears to follow, 
by analogy from what we know of the rest 
■of the universe, that they must be kept 
asunder by motion. From this inference 
w'e shall be led to consider natural masses 
as distinct systems of revolving particles ; 
comparable with those nebulae which oc- 
cupy the celestial spaces, and of which the 
parts are, no doubt, governed by cometary 
and planetary revolutions. It is much to 
be regretted, that the mathematical consi- 
deration of this subject by Mr. Bu6e, in a 
work announced in Nicholson’s Journal, 
vol. iii. p. 234, quarto series, has not yet 
been laid before the public. 
The ordinary appearances of bodies in a 
state of combustion may be explained in a 
general way by attending to the state of 
the bodies which undergo it. If the parts 
of an ignited body, such as that of a piece 
of charcoal, become oxygenated, previous 
to, or at, the very instant of their separa- 
tion from the mass, there will be no ap- 
pearance of light but at the surface of the 
burning body ; but if small parts of the 
body be separated from the general mass, 
during the very process of combustion, and 
before it is completed, as happens 'mecha- 
nically when the particles of iron are torn 
off by the action of a dry grindstone, or 
chemically when the particles of fat rise in 
vapour from the wick of a lighted candle, 
a burning mass will be seen, variable in its 
figure, which, in the latter case, is called 
flame. And that this explanation accounts 
for the flame of burning bodies, is mani- 
fested from the little difference between the 
two phenomena here mentioned, and the 
still less difference between the results, 
namely flame, which are produced by pro- 
jecting the dust of rosin, or a stream of 
hydrogen, through the flame of a candle. 
According to the theory which supposes 
caloric to be an independent substance, 
combustion must be a rapid union of oxy- 
gen with a combustible body; and the heat 
has been srq)posed to be given out from the 
oxygen during a condensation of this last, 
which, it is imagined, takes place univer- 
sally in this process. This, however, has 
not been proved. 
Dr. Thomson, considering caloric and 
light as distinct substances, has adduced 
many facts and observations to prove that 
as caloric abounds in oxygen, so light is a 
component part of every combustible. And 
thence, according to his doctrine, white 
the base of oxygen combines with the base 
of the combustible, the caloric of the one 
and the light of the other unite in the form 
of fire. From this theory he shows, why 
in the transitions of oxygen from one com- 
bustible base to anotlrer, the act of com- 
bustion does not take place ; namely, be- 
cause the caloric of the oxygen has no light 
presented to it to combine witli. The 
whole doctrine, though undoubtedly re- 
quiring further developement and proof, is 
