prevented from ascertaining the quantity disengaged with rigorous
exactness. In the next place, when we are obliged to employ heat, or
when heat is produced by the process, a part of the acid distills, and
mixes with the water of the pneumato-chemical apparatus, by which means
we are deceived in our calculation of the quantity of acid decomposed.
Besides these, the water in the cistern of the apparatus absorbs all the
gas produced which is susceptible of absorption, and renders it
impossible to collect these without loss.
To remedy these inconveniencies, I at first used a bottle with two
necks, Pl. VII. Fig. 3. into one of which the glass funnel BC is luted
so as to prevent any air escaping; a glass rod DE is fitted with emery
to the funnel, so as to serve the purpose of a stopper. When it is used,
the matter to be dissolved is first introduced into the bottle, and the
acid is then permitted to pass in as slowly as we please, by raising the
glass rod gently as often as is necessary until saturation is produced.
Another method has been since employed, which serves the same purpose,
and is preferable to the last described in some instances. This consists
in adapting to one of the mouths of the bottle A, Pl. VII. Fig. 4. a
bent tube DEFG, having a capillary opening at D, and ending in a funnel
at G. This tube is securely luted to the mouth C of the bottle. When any
liquid is poured into the funnel, it falls down to F; and, if a
sufficient quantity be added, it passes by the curvature E, and falls
slowly into the bottle, so long as fresh liquor is supplied at the
funnel. The liquor can never be forced out of the tube, and no gas can
escape through it, because the weight of the liquid serves the purpose
of an accurate cork.
To prevent any distillation of acid, especially in dissolutions
accompanied with heat, this tube is adapted to the retort A, Pl. VII.
Fig. 1. and a small tubulated recipient, M, is applied, in which any
liquor which may distill is condensed. On purpose to separate any gas
that is absorbable by water, we add the double necked bottle L, half
filled with a solution of caustic potash; the alkali absorbs any
carbonic acid gas, and usually only one or two other gasses pass into
the jar of the connected pneumato-chemical apparatus through the tube
NO. In the first chapter of this third part we have directed how these
are to be separated and examined. If one bottle of alkaline solution be
not thought sufficient, two, three, or more, may be added.
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