PURIFICATION of GoLn and SILVER, by antimony. (Under the article ASSAY and METALLURGY, this has been partly treated of.) The gold is to be melted in a crucible large enough to contain thrice the quantity of metal. When the gold is melted, twice its weight of sulphuret of antimony powdered is to be thrown upon it, the crucible is to be covered, and left some minutes in fusion ; after which, when the mixture is well fused, and so hot that its surface sparkles, it is quickly to be poured into an iron cone, previous ly heated and greased. This matter con sists, when cold, of two substances : the upper one of the sulphur of the antimony, United with the metals with which the gold was alloyed, and the lower is the gold united with a quantity of the anti mony proportionable to the quantity of metals which have been separated from the'gold, and which are now united with the sulphur of the antimony.
As a single fusion is not generally suf ficient to disengage the gold from all its alloy, it ought to be fused again in the same manner, and with the same quanti ty of sulphuret of antimony. When
these first fusions have been well made, the gold obtained is alloyed with antimo ny only.
It is then to be put into a large cruci ble, and heated sufficiently to keep it in good fusion. With this heat the antimo ny will be dissipated into smoke, and the operation must be performed slowly, but may be abridged by blowing on the sur face of the metallic mass, which greatly assists in the oxidation and evaporation of all bodies, and particularly of antimo ny. The purification is completed by means of a little nitric thrown into the crucible, which effectually oxides the re maining antimony. Sometimes the gold is deprived of its usual ductility, which is restored by fusing it with nitre and borax.