bodies with the requisite precision as to quantity and proportion; it is
certainly proper to endeavour to simplify these, and to render them less
costly; but this ought by no means to be attempted at the expence of
their conveniency of application, and much less of their accuracy.
SECT. III.
_Some other methods of measuring the volume of Gasses._
The gazometer described in the foregoing section is too costly and too
complicated for being generally used in laboratories for measuring the
gasses, and is not even applicable to every circumstance of this kind.
In numerous series of experiments, more simple and more readily
applicable methods must be employed. For this purpose I shall describe
the means I used before I was in possession of a gazometer, and which I
still use in preference to it in the ordinary course of my experiments.
Suppose that, after an experiment, there is a residuum of gas, neither
absorbable by alkali nor water, contained in the upper part of the jar
AEF, Pl. IV. Fig. 3. standing on the shelf of a pneumato-chemical
apparatus, of which we wish to ascertain the quantity, we must first
mark the height to which the mercury or water rises in the jar with
great exactness, by means of slips of paper pasted in several parts
round the jar. If we have been operating in mercury, we begin by
displacing the mercury from the jar, by introducing water in its stead.
This is readily done by filling a bottle quite full of water; having
stopped it with your finger, turn it up, and introduce its mouth below
the edge of the jar; then, turning down its body again, the mercury, by
its gravity, falls into the bottle, and the water rises in the jar, and
takes the place occupied by the mercury. When this is accomplished, pour
so much water into the cistern ABCD as will stand about an inch over the
surface of the mercury; then pass the dish BC, Pl. V. Fig. 9. under the
jar, and carry it to the water cistern, Fig. 1. and 2. We here exchange
the gas into another jar, which has been previously graduated in the
manner to be afterwards described; and we thus judge of the quantity or
volume of the gas by means of the degrees which it occupies in the
graduated jar.
There is another method of determining the volume of gas, which may
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