one foot each, into water, the fluid gradually insinuates itself into
their pores, and the pieces of wood are augmented both in weight and
magnitude: But each species of wood will imbibe a different quantity of
water; the lighter and more porous woods will admit a larger, the
compact and closer grained will admit of a lesser quantity; for the
proportional quantities of water imbibed by the pieces will depend upon
the nature of the constituent particles of the wood, and upon the
greater or lesser affinity subsisting between them and water. Very
resinous wood, for instance, though it may be at the same time very
porous, will admit but little water. We may therefore say, that the
different kinds of wood possess different capacities for receiving
water; we may even determine, by means of the augmentation of their
weights, what quantity of water they have actually absorbed; but, as we
are ignorant how much water they contained, previous to immersion, we
cannot determine the absolute quantity they contain, after being taken
out of the water.
The same circumstances undoubtedly take place, with bodies that are
immersed in caloric; taking into consideration, however, that water is
an incompressible fluid, whereas caloric is, on the contrary, endowed
with very great elasticity; or, in other words, the particles of caloric
have a great tendency to separate from each other, when forced by any
other power to approach; this difference must of necessity occasion
very considerable diversities in the results of experiments made upon
these two substances.
Having established these clear and simple propositions, it will be very
easy to explain the ideas which ought to be affixed to the following
expressions, which are by no means synonimous, but possess each a strict
and determinate meaning, as in the following definitions:
_Free caloric_, is that which is not combined in any manner with any
other body. But, as we live in a system to which caloric has a very
strong adhesion, it follows that we are never able to obtain it in the
state of absolute freedom.
_Combined caloric_, is that which is fixed in bodies by affinity or
elective attraction, so as to form part of the substance of the body,
even part of its solidity.
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