should be done at a time, and when finished, it should be labelled and
wrapped up, or bottled, before starting on a fresh sample.

When an ore requires to be very finely ground in an agate mortar, it is
often advisable to mix with a little pure alcohol and rub until free
from grit; dry at 100∞ C. and mix well before weighing.

When an assay is required of a quantity of ore made up of parcels of
different weight and quality, each parcel should be separately sampled
and parts of each sample, bearing to each other the same proportion by
weight as the original parcels, should be taken and mixed. For example,
a lot of ore is made up of one parcel of A, 570 tons, one of B, 180
tons, and another of C, 50 tons; a sample representing the whole may be
got by mixing 57 parts of a sample of A with 18 parts of a sample of B,
and 5 parts of a sample of C.

[Illustration: FIG. 2.]

A bruising plate, like that in fig. 2, is convenient for general office
work. The slab is of cast iron, about an inch thick. It is firmly
supported on a solid block of wood, and pivoted for convenience in
emptying. The bruising-hammer is steel-faced, about 4 inches square, and
1-1/2 inch thick. The block is firmly fixed to a small table or tressel,
so that the slab is about 2 feet 6 inches from the ground. The slab is
cleaned, and the sample collected with the help of a stiff-haired brush.

~Drying: Determination of Moisture.~--In practice, the moisture is
generally determined by the samplers, and the proportion is specified in
grains per pound on the label attached to the sample when it reaches the
assay office. The method adopted is usually to dry 1 lb. = 7000 grs. of