be of the Cornish type, short and open, not long and narrow. For
calcinations, _roasting dishes_ are useful: these are broad and shallow,
not unlike saucers, but unglazed. In those cases in which the products
of the roasting are liquid at the temperature used, a _scorifier_ (fig.
38) is suitable if it is desired to keep the liquid; but if the liquid
is best drained off as quickly as it is formed, a _cupel_ (fig. 5)
should be used.

[Illustration: FIG. 5.]

A scorifier is essentially a roasting dish sufficiently thick to resist,
for a time, the corrosive action of the fused metallic oxides it is to
contain. The essential property of a cupel is, that it is sufficiently
porous to allow the fused oxide to drain into it as fast as it is
formed. It should be large enough to absorb the whole of the liquid; and
of course must be made of a material upon which the liquid has no
corrosive action. Cupels do not bear transport well; hence the assayer
generally has to make them, or to supervise their making. A quantity of
bone ash is carefully mixed with water so that no lumps are formed, and
the mixture is then worked up by rubbing between the hands. The bone ash
is sufficiently wet when its cohesion is such that it can be pressed
into a lump, and yet be easily crumbled into powder. Cupel moulds should
be purchased. They are generally made of turned iron or brass. They
consist of three parts (1) a hollow cylinder; (2) a disc of metal; and
(3) a piston for compressing the bone ash and shaping the top of the
cupel. The disc forms a false bottom for the cylinder. This is put in
its place, and the cylinder filled (or nearly so) with the moistened
bone ash. The bone ash is then pressed into shape with the piston, and
the cupel finished with the help of three or four smart blows from a
mallet. Before removing the piston, turn it half-way round upon its axis