i 5 4 ' C H E M ! 
in caloric, which of itfelf is the moft attenuate, fubtile, 
light, and elaftic, of all natural fubftances; accordingly 
its weight cannot be eftimated. 
While caloric feparates the particles of bodies, and di- 
mi nifties their attraction for each other, it proportion¬ 
ally augments their attraction for the particles of adja¬ 
cent bodies. For this rea’fon it is fucceisfully employed 
to produce combinations, and facilitate reciprocal uni¬ 
ons. Hence the axiom, corpora non agunt, n ji foluta,ho- 
dies do not aft, unlefs they be diffolved. Every parti¬ 
cular body differing from others both in the form of its- 
particles and their reparation from each other, requires a 
different quantity of caloric toraife it to the fame tempe¬ 
rature ; this is what is called the capacity of bodies for 
caloric. From this it follows, that different bodies, at 
the fame temperature, or indicating the fame degree of 
the thermometer, ready contain different quantities of 
caloric. This different quantity of caloric contained in 
bodies railed to the fame temperature, which is with pro¬ 
priety termed fpecific caloric, being incapable of being 
meaftired by the thermometer, a mode of ascertaining it 
has been invented, by means of the quantity of ice which 
bodies at an equal temperature will diffolve in defend¬ 
ing to the fame degree. The difference of the quantity 
dilfolved, gives the proportion of caloric contained in 
the feveral bodies, and the inftrument employed to af- 
certain this difference, is called a calorimeter. 
All the experiments made by the modern philofophers, 
who have inveftigated the theory of caloric, prove, that 
bodies, in changing their Hate, change alfo their capacity. 
We call change of Hate in bodies, their becoming iolid, 
liquid, or elattic fluid. Hence it follows, that by mixing 
two (olid bodies at different temperatures, incapable, of 
combining together, a mean of the two temperatures 
will be obtained, if their capacities be equal; but, iftheir 
capacities be unequal, the temperature of the mixture 
will deviate more or iefs from the mean, and the differ¬ 
ence will indicate the reciprocal capacities of the two 
bodies. Thefe phenomena lliow, that caloric has differ¬ 
ent attractions, or different degrees of affinity, for differ¬ 
ent bodies. In all combinations, therefore, this varying 
attraftion of caloric fhould be attentively calculated. 
Wnen bodies unite, either they lofe caloric, which in¬ 
dicates, that the new compound contains lefs than its 
component parts; and in this cafe the operation renders 
heat perceptible to our organs, and the temperature of 
the mixture is increaled, which commonly takes place 
in our experiments: or the bodies which combine' ab- 
lorb caloric, and the new compound contains more heat 
than its component parts did ieparately ; and then, when 
the combination takes place, the mixture grows cold, 
the caloric, which was at liberty between its particles, 
unites with them more clofely, and they even take fome 
from contiguous bodies. Sometimes caloric adheres lb 
forcibly to bodies, that it prevents their combining with 
others. Thus many diffolved into gas, or elaftic fluid, 
unite neither with other bodies, nor with one another, 
as long as they retain this ftate of invifible iblution in 
caloric; fo that recourfe mult be had to double attrac¬ 
tions to effect their combination. 
The attraction of caloric for fome fubftances, is fo great, 
that it is very frequently employed with advantage for 
feparating thefe fubftances from the compounds into which 
they enter, and for analyfing or decompofmg compound 
bodies. Thisis whatwedoindiftiilation, and in all the de- 
compofitions elfeftedby means of fire alone, or caloric, 
applied to very compound fubftances. The different ele¬ 
ments of thefe compounds are gradually diffolved in the or¬ 
der of theirfolubility in caloric, and feparated in the ftate of 
vapour or gas. Light, applied at the fame time with ca¬ 
loric, frequently alfifts its aftion, or has its aftion affifted 
by it. Hence, tranl'parent veffels employed in furnaces 
are extremely ufeful to chemilts, by tranfmitting light 
and caloric at the fame time. A fimilar effect is produ¬ 
ced, by penetrating opake veffels fo thoroughly with ca~ 
a 
. S T R Y. 
loric, as to make them red-hot, or render them permea¬ 
ble to light. 
There are bodies which abforb caloric much more 
fpeedily than others; this is called the property of con- 
dufting caloric. In general thofe bodies which are 
molt coloured are the belt conduftors. The caufe of 
this phenomenon is unknown. All thefe fafts prove, 
that caloric is a particular fubftance, and not a modifica¬ 
tion. or all fubftances, as fome natural philofophers have 
imagined; and it is far from having been fliown to be 
the fame thing with light; for the farther we advance in 
the fcience. of phy.fics, the greater differences appear in 
the aftion of thefe two fubftances. Thefe fafts point out 
to us the principles and nature of the dilatation of folids 
and the rarefaction of fluids: thermometers: fufion; 
fublimation and volatilization: the calorimeter, and ta¬ 
bles of the fpecific heat of bodies:, the changes of tem¬ 
perature in different mixtures: artificial refrigeration; 
the.production of gales, and their fixation: diftiliation 
at different temperatures: incandeicence : the different 
conduftors of caloric ; and attractions of the fame. 
THE ACTION OF THE AIK. 
The air afts in a collective mafs on all natural bodies, 
by its weight, moiiture or drynefs, temperature, See. Ac¬ 
cordingly experiments of fynthefis or analyfis, made in 
contaCt with the air, differ confiderably.from thofe which 
are performed in a vacuum; and it is always neceffary to af- 
certain the ftate of the barometer, thermometer, and hy¬ 
grometer, in chemical experiments. The atmofphere it- 
lelfisa vail laboratory, in which nature operates im- 
menfe analyfes, folutions, precipitations, and combina¬ 
tions: it is a grand receiver, in which all the attenuated 
and volatilized productions of terreftrial bodies are re¬ 
ceived, mingled, agitated, combined, and feparated. 
Confidered in this view, the atmofpheric air is a chaos, 
an indeterminate mixture of mineral v.apours, vegetable 
and animal molecules, feeds, and eggs, which the lumi¬ 
nous, caloric, and eleftric, fluids, are pervading and tra¬ 
veling continually. The grand changes it experiences, 
and of which we are fenfible in extenllve lpaces by the 
appearance of water, light, free caloric, cr noife, are call¬ 
ed meteors. Yet notwithftanding this mixture, of 
which it feems impoffible for us to afeertain the nature, 
the atmofpheric air is lenfibly the fame with regard to 
its intimate qualities, wherever we examine it; and it is 
decidedly marked by its two properties of lupporting 
refpiration and combuftion, the cloftit analogy lubiift- 
ing between thefe two grand phenomena. From a care¬ 
ful ftudy of what pafies in combuftion, we may readily 
acquire a knowledge of the air. 
Acombultible body cannot burn without the contaft 
of atmofpheric air, or a certain matter extracted from it; 
and hence combuftion cannot take place in a vacuum. 
A combuflible body cannot burn in a given quantity of 
atmofpheric air, beyond a certain period. A hundred 
parts of this air contain only twenty-feven capable of 
lupporting combuftion; when thefe twenty-feven parts 
have been abforbed by the combuflible body, the com¬ 
buftion ceafes, as the other feventy-three parts cannot at 
all contribute to its fupport. Hence it appears, that at¬ 
mofpheric air is a compound of two different fubftances, 
fetting afide a few matters foreign to it, which are min¬ 
gled with it, but amount not to more than a hundredth 
part of its bulk. Of thefe two fubftances, one fupports 
refpiration and combuftion: this is termed vital air; the 
other is the reverie of it in both thefe refpefts, and is cal¬ 
led azotic gas. Thus a body burning in the air effefts a 
real analyfis of this fluid. It feparates from it, and ab- 
forbs, the vital air, which augments the weight and chang¬ 
es the nature of the burning body. The azotic gas 
which remains is lighter than the atmofpheric air, ex- 
tingujfhes bodies in combuftion and kills animals. It is 
alio one of the conilituent principles of feveral com¬ 
pounds, as we Hull hereafter fee, particularly of ammo¬ 
niac, 
