In some cases
this preliminary scorification is advantageous or even necessary: this
may be because the lead is hard and impure, or it may be that a very
small button of gold is expected. In the latter case it is best to
scorify the lead down to something less than 1 gram, and to perform the
cupellation on a specially prepared small fine cupel. These small cupels
are best made by grinding the unsaturated portion of a used cupel to a
fine powder, and compressing the dry powder into a small Berlin crucible
or scorifier; the face should be made quite smooth by pressure from a
pestle. On such cupels a small speck of gold (less than .01 milligram)
will be left in a good shape and easily visible; but the cupel must be
withdrawn from the muffle as soon as the cupellation is finished to make
sure of always getting the button in good condition. In places, such as
Mints, where large numbers of bullion assays are regularly made a
special form of cupel is used so that not less than six dozen assays may
all be cupelled at the same time in a muffle of ordinary size. These
cupels are square blocks, a little less than 2 inches across, and a
little more than three quarters of an inch deep. Each block carries four
hollows of about .7 inch across and .3 inch deep. A muffle, on a floor
space of 6 inches by 12, would take 3 of these blocks abreast and 6
deep, and thus provide the means for 72 assays.
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