moderate heat, whilst others, as sulphat of potash, lime, &c. require
the strongest fires we are capable of producing. This liquifaction of
salts by caloric produces exactly the same phenomena with the melting of
ice; it is accomplished in each salt by a determinate degree of heat,
which remains invariably the same during the whole time of the
liquifaction. Caloric is employed, and becomes fixed during the melting
of the salt, and is, on the contrary, disengaged when the salt
coagulates. These are general phenomena which universally occur during
the passage of every species of substance from the solid to the fluid
state of aggregation, and from fluid to solid.
These phenomena arising from solution by caloric are always less or more
conjoined with those which take place during solutions in water. We
cannot pour water upon a salt, on purpose to dissolve it, without
employing a compound solvent, both water and caloric; hence we may
distinguish several different cases of solution, according to the nature
and mode of existence of each salt. If, for instance, a salt be
difficultly soluble in water, and readily so by caloric, it evidently
follows, that this salt will be difficultly soluble in cold water, and
considerably in hot water; such is nitrat of potash, and more especially
oxygenated muriat of potash. If another salt be little soluble both in
water and caloric, the difference of its solubility in cold and warm
water will be very inconsiderable; sulphat of lime is of this kind. From
these considerations, it follows, that there is a necessary relation
between the following circumstances; the solubility of a salt in cold
water, its solubility in boiling water, and the degree of temperature at
which the same salt liquifies by caloric, unassisted by water; and that
the difference of solubility in hot and cold water is so much greater in
proportion to its ready solution in caloric, or in proportion to its
susceptibility of liquifying in a low degree of temperature.
The above is a general view of solution; but, for want of particular
facts, and sufficiently exact experiments, it is still nothing more than
an approximation towards a particular theory. The means of compleating
this part of chemical science is extremely simple; we have only to
ascertain how much of each salt is dissolved by a certain quantity of
water at different degrees of temperature; and as, by the experiments
published by Mr de la Place and me, the quantity of caloric contained in
a pound of water at each degree of the thermometer is accurately known,
it will be very easy to determine, by simple experiments, the proportion
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