DECOCTION, usually signifies either the action
of boiling a substance in water, or the water itself in
which the substance has been boiled. It is only appli-
cable to matters containing some principles soluble in
water: such particularly are animal and vegetable
matters. Decoction ought not to be used with such
substances as contain any volatile principles, as they
would be dissipated in the air during the process. But
it may be safely used, nay even becomes necessary, when
the matters to be treated are solid, and of a close and
compact texture; because then the water could not
extract its principles without a boiling heat. Most soft
animal matters, as flesh, skin, tendons, may be con-
veniently boiled in water; because they contain no prin-
ciple volatile with a boiling heat. Water extracts from
them nothing but a gelatinous substance, and some
oily parts which float on the surface of the water. All
vegetable matters which are inodorous, and particular-
ly those which are hard, as roots, barks, &c. are gen-
erally boiled, when an extraction of their principles
by water is required.—To this rule, however, there
are some exceptions. Peruvian bark, for instance, gives
its strength to cold water better than to such as is boil-
ing hot. Many other vegetables also have the same
property of yielding less to boiling than to cold water.
And therefore a general rule may be established, that
decoction ought not to be employed but when abso-
lutely necessary; that is, when the same principles, or
the same quantities of those principles, cannot be ob-
tained by an infusion, and that without heat, if it can
be so done, considering that the proximate principles
of
of vegetables are generally so delicate, and so susceptible of change and decomposition, that frequently the most gentle heat changes much their nature and properties.