CHAP. IV.
_Of Mechanical Operations for Division of Bodies._
SECT. I.
_Of Trituration, Levigation, and Pulverization._
These are, properly speaking, only preliminary mechanical operations for
dividing and separating the particles of bodies, and reducing them into
very fine powder. These operations can never reduce substances into
their primary, or elementary and ultimate particles; they do not even
destroy the aggregation of bodies; for every particle, after the most
accurate trituration, forms a small whole, resembling the original mass
from which it was divided. The real chemical operations, on the
contrary, such as solution, destroy the aggregation of bodies, and
separate their constituent and integrant particles from each other.
Brittle substances are reduced to powder by means of pestles and
mortars. These are of brass or iron, Pl. I. Fig. 1.; of marble or
granite, Fig. 2.; of lignum vitae, Fig. 3.; of glass, Fig. 4.; of agate,
Fig. 5.; or of porcellain, Fig. 6. The pestles for each of these are
represented in the plate, immediately below the mortars to which they
respectively belong, and are made of hammered iron or brass, of wood,
glass, porcellain, marble, granite, or agate, according to the nature of
the substances they are intended to triturate. In every laboratory, it
is requisite to have an assortment of these utensils, of various sizes
and kinds: Those of porcellain and glass can only be used for rubbing
substances to powder, by a dexterous use of the pestle round the sides
of the mortar, as it would be easily broken by reiterated blows of the
pestle.
The bottom of mortars ought to be in the form of a hollow sphere, and
their sides should have such a degree of inclination as to make the
substances they contain fall back to the bottom when the pestle is
lifted, but not so perpendicular as to collect them too much together,
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