certain height, more oil rises through its capillary tubes than the
stream of air is capable of consuming, and smoke is produced. Hence it
is necessary to be able to lengthen or shorten the wick without opening
the apparatus; this is accomplished by means of the rod 31, 32, 33, 34,
which passes through a leather-box, and is connected with the support of
the wick; and that the motion of this rod, and consequently of the wick,
may be regulated with the utmost smoothness and facility; it is moved at
pleasure by a pinnion which plays in a toothed rack. The rod, with its
appendages, are represented Pl. XII. Fig. 3. It appeared to me, that the
combustion would be assisted by surrounding the flame of the lamp with a
small glass jar open at both ends, as represented in its place in Pl.
XI.
I shall not enter into a more detailed description of the construction
of this apparatus, which is still capable of being altered and modified
in many respects, but shall only add, that when it is to be used in
experiment, the lamp and reservoir with the contained oil must be
accurately weighed, after which it is placed as before directed, and
lighted; having then formed the connection between the air in the
gazometer and the lamp, the external jar A, Pl. XI. is fixed over all,
and secured by means of the board BC and two rods of iron which connect
this board with the lid, and are screwed to it. A small quantity of oil
is burnt while the jar is adjusting to the lid, and the product of that
combustion is lost; there is likewise a small portion of air from the
gazometer lost at the same time. Both of these are of very
inconsiderable consequence in extensive experiments, and they are even
capable of being valued in our calculation of the results.
In a particular memoir, I shall give an account to the Academy of the
difficulties inseparable from this kind of experiments: These are so
insurmountable and troublesome, that I have not hitherto been able to
obtain any rigorous determination of the quantities of the products. I
have sufficient proof, however, that the fixed oils are entirely
resolved during combustion into water and carbonic acid gas, and
consequently that they are composed of hydrogen and charcoal; but I have
no certain knowledge respecting the proportions of these ingredients.
SECT. V.
278