retort, while the azote, combining with a part of the hydrogen, forms
ammoniac, or volatile alkali.
Animal substances, being composed nearly of the same elements with
cruciferous plants, give the same products in distillation, with this
difference, that, as they contain a greater quantity of hydrogen and
azote, they produce more oil and more ammoniac. I shall only produce one
fact as a proof of the exactness with which this theory explains all the
phenomena which occur during the distillation of animal substances,
which is the rectification and total decomposition of volatile animal
oil, commonly known by the name of Dippel's oil. When these oils are
procured by a first distillation in a naked fire they are brown, from
containing a little charcoal almost in a free state; but they become
quite colourless by rectification. Even in this state the charcoal in
their composition has so slight a connection with the other elements as
to separate by mere exposure to the air. If we put a quantity of this
animal oil, well rectified, and consequently clear, limpid, and
transparent, into a bell-glass filled with oxygen gas over mercury, in a
short time the gas is much diminished, being absorbed by the oil, the
oxygen combining with the hydrogen of the oil forms water, which sinks
to the bottom, at the same time the charcoal which was combined with the
hydrogen being set free, manifests itself by rendering the oil black.
Hence the only way of preserving these oils colourless and transparent,
is by keeping them in bottles perfectly full and accurately corked, to
hinder the contact of air, which always discolours them.
Successive rectifications of this oil furnish another phenomenon
confirming our theory. In each distillation a small quantity of charcoal
remains in the retort, and a little water is formed by the union of the
oxygen contained in the air of the distilling vessels with the hydrogen
of the oil. As this takes place in each successive distillation, if we
make use of large vessels and a considerable degree of heat, we at last
decompose the whole of the oil, and change it entirely into water and
charcoal. When we use small vessels, and especially when we employ a
slow fire, or degree of heat little above that of boiling water, the
total decomposition of these oils, by repeated distillation, is greatly
more tedious, and more difficultly accomplished. I shall give a
particular detail to the Academy, in a separate memoir, of all my
experiments upon the decomposition of oil; but what I have related above
may suffice to give just ideas of the composition of animal and
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