Weigh both portions
and assay separately. _Sifting should be followed by a very thorough
mixing._
7. _If a metal or alloy in bar or ingot:_ clean the upper surface of the
bar, and bore through the bar. Use the borings. If the ingot or bar is
small, cut it through and file the section. Filings must be freed from
fragments of the file by means of a magnet; and from oil, if any be
present, by washing with a suitable solvent.[1] Where practicable,
metals and alloys are best sampled by melting and granulating. The
student must carefully avoid any chance of mixing dirt or particles of
other samples with the particular sample which he is preparing. One ore
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.
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