distance, and the interval is filled up with sand. At the inferior
extremity K of the inner tube, a glass tube is fixed, to which we adopt
the Argand lamp LM for burning alkohol, &c.
Things being thus disposed, and the lamp being filled with a determinate
quantity of alkohol, it is set on fire; the water which is formed during
the combustion rises in the chimney KE, and being condensed in the worm,
runs out at its extremity F into the bottle P. The double tube of the
chimney, filled with sand in the interstice, is to prevent the tube from
cooling in its upper part, and condensing the water; otherwise, it
would fall back in the tube, and we should not be able to ascertain its
quantity, and besides it might fall in drops upon the wick, and
extinguish the flame. The intention of this construction, is to keep the
chimney always hot, and the worm always cool, that the water may be
preserved in the state of vapour whilst rising, and may be condensed
immediately upon getting into the descending part of the apparatus. By
this instrument, which was contrived by Mr Meusnier, and which is
described by me in the Memoirs of the Academy for 1784, p. 593. we may,
with attention to keep the worm always cold, collect nearly seventeen
ounces of water from the combustion of sixteen ounces of alkohol.
SECT. VIII.
_Of the Oxydation of Metals._
The term _oxydation_ or _calcination_ is chiefly used to signify the
process by which metals exposed to a certain degree of heat are
converted into oxyds, by absorbing oxygen from the air. This combination
takes place in consequence of oxygen possessing a greater affinity to
metals, at a certain temperature, than to caloric, which becomes
disengaged in its free state; but, as this disengagement, when made in
common air, is slow and progressive, it is scarcely evident to the
senses. It is quite otherwise, however, when oxydation takes place in
oxygen gas; for, being produced with much greater rapidity, it is
generally accompanied with heat and light, so as evidently to show that
metallic substances are real combustible bodies.
All the metals have not the same degree of affinity to oxygen. Gold,
silver, and platina, for instance, are incapable of taking it away from
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