1817.) On the Chemical Phenomena of Heat. 429 
tilize without becoming previously fluid; yet, under strong atmos- 
pheric pressure, they are easily fusible. Also water, confined under 
the receiver.of a powerful air-pump, exposed toan extensive surface 
of concentrated sulphuric acid, is congealed; the vapour, which is 
continually emitted by reason of the vacuum, which is preserved 
nearly perfect by the sulphuric acid, robs the residuary water of so 
much of its caloric as to congeal it, and the ice itself evaporates 
without undergoing liquefaction. Here we see the capacity of this 
exceedingly rare vapour is enormous; it is entirely owing to. this 
that itis able, in the first instance, to congeal the water. We must 
next ascertain the manner in which the atmospheric pressure pre- 
serves bodies in a state of fluidity. 
Under the pressure of an atmosphere, a liquid cannot be 
made to boil till its particles are separated to such a distance 
that the particles of which the atmosphere is composed can enter 
into the interstices: the repulsive force so far exceeds the cen- 
tripetal that it can overcome this atmospheric pressure. Hence 
we should be led to expect all liquids to have their point of 
ebullition depressed an equal number of degrees when in vacuo: 
this appears, from the experiments of the late Dr. Robinson, to 
be the fact. Hence we see that the pressure being invariable, 
the point of ebullition of a liquid is constant; also we perceive, 
on account of atmospheric pressure, the sudden and remark- 
able change which bodies undergo during their conversion into 
aeriform fluids ; also the immense quantity of caloric which at this 
moment becomes latent; the particles which were previously re- 
moved from each other only a portion of the diameter of any single 
particle, are now separated 10, 12, or more diameters ; and though 
the calorific atmosphere at this distance is very rare, its great extent 
produces the change of capacity which the body undergoes during 
this change of form. Gases, under ordinary circumstances, are 
subjected to peculiar laws; collected as usual, they all possess the 
same degree of elastic force, 7. e. the excess of the centrifugal 
above the centripetal force, is constant, = generally to 29 inches 
of mercury ; hence the specific gravity of any gas depends upon the 
real weight of an atom, the attraction of its particles for each other 
and for caloric. Here if we assume the centripetal force to vary 
= » and take the common expression of the variation of the density 
74 
t . 1 
of an atmosphere surrounding a sphere, h x h y log. — = r — — 
(Dealtry’s Flux.), we shall find a ratio between the increase of tem- 
perature and the expansion of aeriform matter, which appears from 
experiment to be the real iaw; the investigation of this point I at 
present omit, deferring it till the whole principles, here briefly 
explained, come under a more strict mathematical examination. 
hen two or more particles of a different kind attract each 
other, they will be acted upon in the same manner as two similar 
