[54] Mr Lavoisier gives, in this part of his work, very accurate
directions for reducing the common subdivisions of the French pound into
decimal fractions, and _vice versa_, by means of tables subjoined to
this 3d part. As these instructions, and the table, would be useless to
the British chemist, from the difference between the subdivisions of the
French and Troy pounds, I have omitted them, but have subjoined in the
appendix accurate rules for converting the one into the other.--E.
[55] Vide Mr Brisson's Essay upon Specific Gravity, p. 5.--A.
[56] For the use of these reagents see Bergman's excellent treatise upon
the analysis of mineral waters, in his Chemical and Physical Essays.--E.
[57] Three or four years ago, I have seen similar glass hydrometers,
made for Dr Black by B. Knie, a very ingenious artist of this city.--E.
CHAP. II.
_Of Gazometry, or the Measurement of the Weight and Volume of Aeriform
Substances._
SECT. I.
_Description of the Pneumato-chemical Apparatus._
The French chemists have of late applied the name of _pneumato-chemical
apparatus_ to the very simple and ingenious contrivance, invented by Dr
Priestley, which is now indispensibly necessary to every laboratory.
This consists of a wooden trough, of larger or smaller dimensions as is
thought convenient, lined with plate-lead or tinned copper, as
represented in perspective, Pl. V. In Fig. 1. the same trough or cistern
is supposed to have two of its sides cut away, to show its interior
construction more distinctly. In this apparatus, we distinguish between
the shelf ABCD Fig. 1. and 2. and the bottom or body of the cistern FGHI
Fig. 2. The jars or bell-glasses are filled with water in this deep
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