of zinc, more than .1 per cent. of copper, or a larger
quantity of silver, it may be likened to a turbid liquor. The
resemblance holds good so far that if the molten lead be further heated,
whereby its solvent power on the added metal is increased, the turbidity
will disappear, or at least be considerably diminished. A portion taken
at random from such a molten metal may, or may not, give a good sample.
The suspended insoluble matter will tend to concentrate itself in the
upper or lower parts of the liquid according to whether it is heavier or
lighter than it; and this separation may occur with extreme slowness or
with fair rapidity. However, it is generally agreed that in the case of
such alloys as occur in practice, samples taken in this way are quite
satisfactory and are the best obtainable. The precautions insisted on
are that the lead shall be made as hot as practicable; that it shall be
stirred up at the time of taking the sample; and that the portion
withdrawn shall be taken out with a ladle at least as hot as the molten
metal. The further precaution that if any dross be on the surface of the
metal it shall be skimmed off and separately sampled and assayed is
almost too obvious to require mention. An alternative and, perhaps,
better way of taking the sample is to withdraw portions at equal
intervals from the stream of metal whilst the pot is being emptied;
equal weights taken from these portions and mixed (by melting or in some
other way) give a fair sample of the whole.
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