Beaume with the speculum of the Abbe Bouriot; but, as the direction of
the reflected rays is necessarily from below upwards, the substance to
be operated upon must be placed in the air without any support, which
renders most chemical experiments impossible to be performed with this
instrument.
For these reasons, I first endeavoured to employ oxygen gas for
combustion, by filling large bladders with it, and making it pass
through a tube capable of being shut by a stop-cock; and in this way I
succeeded in causing it to support the combustion of lighted charcoal.
The intensity of the heat produced, even in my first attempt, was so
great as readily to melt a small quantity of crude platina. To the
success of this attempt is owing the idea of the gazometer, described p.
308. _et seq._ which I substituted instead of the bladders; and, as we
can give the oxygen gas any necessary degree of pressure, we can with
this instrument keep up a continued stream, and give it even a very
considerable force.
The only apparatus necessary for experiments of this kind consists of a
small table ABCD, Pl. XII. Fig. 15, with a hole F, through which passes
a tube of copper or silver, ending in a very small opening at G, and
capable of being opened or shut by the stop-cock H. This tube is
continued below the table at l m n o, and is connected with the
interior cavity of the gazometer. When we mean to operate, a hole of a
few lines deep must be made with a chizel in a piece of charcoal, into
which the substance to be treated is laid; the charcoal is set on fire
by means of a candle and blow-pipe, after which it is exposed to a
rapid stream of oxygen gas from the extremity G of the tube FG.
This manner of operating can only be used with such bodies as can be
placed, without inconvenience, in contact with charcoal, such as metals,
simple earths, &c. But, for bodies whose elements have affinity to
charcoal, and which are consequently decomposed by that substance, such
as sulphats, phosphats, and most of the neutral salts, metallic glasses,
enamels, &c. we must use a lamp, and make the stream of oxygen gas pass
through its flame. For this purpose, we use the elbowed blow-pipe ST,
instead of the bent one FG, employed with charcoal. The heat produced in
this second manner is by no means so intense as in the former way, and
is very difficultly made to melt platina. In this manner of operating
with the lamp, the substances are placed in cuppels of calcined bones,
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