arts and manufactures. The methods of assaying are mainly those of
analytical chemistry, and are limited by various practical
considerations to the determination of the constituents of a small
parcel, which is frequently only a few grains, and rarely more than a
few ounces, in weight. From these determinations calculations are made,
which have reference to a mass of material of, perhaps, hundreds of
tons. But in all cases, whether the mass under consideration be large or
small, whether the material be obtained by mining, grown, or
manufactured, the assayer is supposed to receive a small quantity,
called "the sample," which is, or ought to be, the exact counterpart of
the mass of material that is being dealt with. The taking and making of
this sample is termed "sampling"; and the men whose special work it is
to select such samples are "the samplers."

But although "sampling" is thus distinct from "assaying," the assayer
should be familiar with the principles of sampling, and rigorous in the
application of these principles in the selecting, from the sample sent
him, that smaller portion upon which he performs his operations.

~Sampling.~--_In the case of gases_, there is absolutely no trouble in
mixing. The only difficulty is in drawing off a fair sample where, as in
flues, the body of the gas is in motion, and varies a little in
composition from time to time. In this case, care must be taken to draw
off uniformly a sufficient volume of the gas during a prolonged period;
any portion of this larger volume may then be taken for the analytical
operation.

_In the case of liquids_, which mix more or less easily--and this class
includes metals, &c., in the state of fusion--more or less severe
agitation, followed by the immediate withdrawal of a portion, will yield