the elementary part to become acquainted with. The whole of this third
part may therefore be considered as resembling the explanations of
plates which are usually placed at the end of academic memoirs, that
they may not interrupt the connection of the text by lengthened
description. Though I have taken great pains to render this part clear
and methodical, and have not omitted any essential instrument or
apparatus, I am far from pretending by it to set aside the necessity of
attendance upon lectures and laboratories, for such as wish to acquire
accurate knowledge of the science of chemistry. These should familiarise
themselves to the employment of apparatus, and to the performance of
experiments by actual experience. _Nihil est in intellectu quod non
prius fuerit in sensu_, the motto which the celebrated Rouelle caused to
be painted in large characters in a conspicuous part of his laboratory,
is an important truth never to be lost sight of either by teachers or
students of chemistry.

Chemical operations may be naturally divided into several classes,
according to the purposes they are intended for performing. Some may be
considered as purely mechanical, such as the determination of the weight
and bulk of bodies, trituration, levigation, searching, washing,
filtration, &c. Others may be considered as real chemical operations,
because they are performed by means of chemical powers and agents; such
are solution, fusion, &c. Some of these are intended for separating the
elements of bodies from each other, some for reuniting these elements
together; and some, as combustion, produce both these effects during the
same process.

Without rigorously endeavouring to follow the above method, I mean to
give a detail of the chemical operations in such order of arrangement as
seemed best calculated for conveying instruction. I shall be more
particular in describing the apparatus connected with modern chemistry,
because these are hitherto little known by men who have devoted much of
their time to chemistry, and even by many professors of the science.

CHAP. I.

_Of the Instruments necessary for determining the Absolute and Specific
Gravities of Solid and Liquid Bodies._

The best method hitherto known for determining the quantities of
substances submitted to chemical experiment, or resulting from them, is
by means of an accurately constructed beam and scales, with properly
regulated weights, which well known operation is