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22 2 MECHANICAL DENTISTRY AND METALLURGY. :

first passed through the dust to remove any particles of iron
which may be present. All organic and other combustible
material is gotten rid of by burning it off in an open fire-
clay crucible, after which suitable fluxes are added and the
remainder is melted. These necessarily vary somewhat,
but the following proportion* may be conveniently taken

Lemel (sweep.) 50 parts.
Sodium carbonate 5 "
Borax 5 "
Potassium bisulphate or nitre I to 2 "
Common salt 5 "
The lemel is well mixed with the fluxes, with the excep-
tion of the salt, which is kept as a cover for the mixture,
as it prevents the mass rising too much and overflowing the
crucible. Nitre wdiich oxidizes the base metals and potas-
sium bisulphate should be sparingly employed. The
crucible should not be more than half full to commence
with, and should be gently heated at first, the temperature
being raised gradually. Towards the end of the operation,
w^hen the violence of the action has nearly ceased, a more
intense heat is employed, and wdien the whole mass is thor-
oughly liquid it is well stirred with an iron rod, after which
the crucible is removed and contents poured into an ingot
mould, care being taken to prevent the " slag " running
into the mould. The ingot thus obtained will in many
cases be in a suitable condition for rolling. If brittle, the
alloy may be " toughened " by remelting with a little char-
coal powder.
When it is desired to obtain the gold in a pure state this
alloy is treated as directed under refining of gold.
Purple-of-Cassius.—This preparation of gold is so
named for its color and its discoverer, M. Cassius. It is
employed by manufacturers of artificial teeth in obtaining

* Smith's Dental Metallurgy.