a fairly representative sample.

_In the case of solids_, the whole mass must be crushed, and, if not
already of fairly uniform quality, mixed, before sampling can take
place. Most of the material which a sampler is called upon to deal with,
is, however, in a more or less divided state and fairly uniform. In
practice it is assumed that 5 per cent. of the whole (= 1/20th), if
taken in portions of equal weight and at frequent and regular intervals,
will represent the mass from which it was taken. Taking a heap of ore,
A, and selecting one out of every twenty spade-, bag-, barrow-, or
wagon-fuls, according to the quantity of stuff in the heap, there is
obtained a second heap, B, containing one-twentieth of the stuff of the
heap A. If we crush the stuff in B until this heap contains
approximately the same number of stones as A did--which means, crushing
every stone in B into about twenty pieces--B will become the counterpart
of A. Selecting in the same manner 5 per cent. of B, there is got a
third heap, C. This alternate reduction and pulverising must be carried
on until a sample of suitable size is obtained. This may be expressed
very clearly thus:--

A = 1000 tons of rocks and lumpy ore.
B = 50 " " rough stones, 1/20th of A.
C = 2.5 " " small stones, 1/20th of B.
D = 0.125 " " coarse powder, 1/20th of C.

[Illustration: FIG. 1.

CONE

PARTLY REDUCED CONE