adopted which will concentrate the whole of the metal (either during or
after solution) in a product which need not necessarily be pure. The
work on this product is comparatively easy. In separating small
quantities of a substance from a large bulk of impurities, the group
separations must not as a rule be too much relied on. Very large
precipitates carry down small quantities of bodies not belonging to the
group, more especially when there is a tendency to form weak double
compounds. The re-dissolving and re-precipitating of bulky precipitates
should be avoided.

When a large number of assays of the same kind have to be carried out, a
plan something like the following is adopted:--The samples, after having
been dried, are placed in order on a table at the left hand of the
assayer. He takes the first, marks it with a number, samples and weighs
up the quantity required, and transfers it to a flask, which is
similarly marked. As the weighings are finished, the samples are placed
in the same order on his right hand. The assistant takes the flasks in
batches of four or five at a time to the fume cupboard, where he adds a
measured quantity of acid. When solution has been effected, dilution
with a measured volume is generally necessary. The assayer sees to this
and (whilst the funnels and filters are being prepared) makes any
separation that is necessary. The filters are arranged in order on a
rack (fig. 11), and need not be marked unless the precipitates or
residues have subsequently to be dried. The filters are washed with hot
water, and if the filtrates are wanted flasks are placed beneath, if
not, the solution is drained off down the sink. Precipitation or
reduction (or whatever it may be) is now made; the assistant filters the
prepared samples, one at a time, whilst the assayer is engaged with the
others. The same style of work is continued until the assays are
completed. If one should be spoiled, it is better to allow it to stand