The portion he
requires should never be taken at hap-hazard; the sample must be reduced
systematically to the quantity required.
1. _If the sample is a liquid:_ it is sufficient to shake the bottle,
and take out a measured or weighed quantity for the assay.
2. _If a liquid with a solid in suspension:_ measure the whole of it.
Filter. Make up the filtrate with the wash-water or water to the
original bulk. Assay it. Dry and weigh the residue, and make a separate
assay of it.
3. _If of a creamy consistency, free from heavy particles:_ mix well;
spread out evenly on a glazed tile. Take up equal portions at equal
distances. Mix and assay.
4. _If a mud of coarse and fine particles, or of particles of unequal
density:_ weigh and transfer to a porcelain dish, or weigh in the dish.
Dry at 100° C., weigh. Treat the residue as a solid capable of being
powdered.
5. _If a solid capable of being powdered, or already powdered:_ heap up
into a cone; flatten with a spatula; divide along two diameters at right
angles, and carefully reject the whole of two alternate quarters,
brushing away any fine powder. Mix the other quarters, and repeat (if
necessary). For small quantities a fine state of division is essential.
6. _If a solid with metallic particles:_ powder and pass through a
sieve; the metallic particles will not pass through.
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