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caloric * and azotic air for oxygen, attracts and fixes within itself oxygen f, 
(the base of oxygen air, for oxygen air is oxygen combined with a certain 
quantity of caloric:). . .hence its increase of weight, and its conversion into an 
oxyd or calx, and hence the azotic, or lethal, air left us in the bell-glass— 
That the temperature being increased* the affinity of the caloric for oxygen 
becoming now superior to the attraction of the mercury, the oxygen is with¬ 
drawn from the oxyd of mercury by the superior attiaction of the calotte,..,, 
hence its decrease vn vueight, and its restoration to futdily and splendour, 
and hence the produce of oxygen, or vital, air,. . .clearly displaying to us this 
important Truth; 
That atmospheric air is actually a compound of two heavy substances, 
azot§ and oxygen; || which bodies, when combined with caloric, or the 
matter of heat, are aeriform, and may be procured in separate states, viz. in 
the condition of azotic and vital airs, which being mixed in a certain pro¬ 
portion, viz. 3 of the former to 1 of the latter, constitutes our atmosphere. 
a firong heat, the caloric expands this fluid; that is, insinuates itself through the body, and separates 
its particles (thermometers depend on this expansive power of fire), and, like the pieces of the bullet 
where sand interposed, the divided particles are no longer subject to the law of cohesion; then it is 
they obey the law of attraction, and each atom of mercury attracts to itself a particle of oxygen, just 
as a loadstone would draw to itself a particle of iron—The loadstone only attracts iron. This repre¬ 
sents the term affinity in chemistry. The mercury did not attract the azot, because chemists would 
say it had no affinity for it. 
* Fire, or the matter of heat. 
f An experimentalist would illustrate this by placing a needle between two magnets of different 
powers. This would represent oxygen between the two attractions of the caloric and azotic air. As 
we may suppose a loadstone to have an attraction for the needle superior to the two magnets, so would 
it draw the needle to itself from these, just as the mercury draws away from the azotic air and caloric 
the oxygen. 
J This is a curious fact; the temperature being increased, the caloric alone overcomes the elective 
attraction of mercury for oxygen, and depriving it of that principle, the attraction of cohesion takes 
place with the particles of mercury, and we obtain then running mercury and oxygen gas. To have 
recourse to the note * P a £V ^9, the oxygen and mercury being separated beyond their sphere of 
attraction, the caloiic attracts to itself oxygen, just as either of the magnets (in the preceding note) 
would again attiact to itself the needle, were it placed within its sphere of attraction, but beyond 
that of the loadstone. 
§ 1 hat azot is a solid substance as well as oxygen, will be proved when we come to treat on 
manures. That the application of heat should render oxygen and azot gaseous, is not wonderful, 
fmce we often observe ice by the admixture of caloric rendered a fluid, and heated to 212, converted 
into an aeriform and transparent gas. The hardest substance in the world, the diamond, may be vola- 
talized in the same way. Mon. D'Arcet took a sphere of porcelain china, and after cutting it into 
halves, confined a diamond in the middle; he then joined the two sections ftrongly together. Putting 
these balls into a furnace, he afterwards unscrewed them, and found the diamonds evaporated, and 
the place which they occupied empty, though he could perceive no chink or fracture any where over 
the surface of the ball! 
|| The distinction betwixt air and vapour is this, both are formed of particles held in suspension 
by caloric, or heat, but by cold, or condensation, vapours return in time to their original form, whereas 
airs continue permanently elastic. 
