They are
chiefly of interest in the metallurgy of nickel, cobalt, and tin. They
are formed by heating the metal or ore in covered crucibles with arsenic
and, if necessary, a reducing agent. The product is fused with more
arsenic under a slag, consisting mainly of borax. They are very fusible,
brittle compounds. On exposure to the air at a red heat the arsenic and
the metal simultaneously oxidize. When iron, cobalt, nickel, and copper
are present in the same speise, they are eliminated in the order
mentioned.
_Slags_ from which metals are to be separated should not be too acid; at
least, in those cases in which the metal is to be reduced from a
compound, as well as separated from earthy impurities. Where the object
is simply to get a button of metal from a substance in which it is
already in the metallic state, but mixed with dross (made up of metallic
oxides, such as those of zinc or iron), from which it is desired to
separate it, an acid flux like borax is best; or, if the metal is easily
fusible, and there would be danger of loss of metal by oxidation or
volatilising, it may be melted under a layer of resin or fat. Common
salt is sometimes used with a similar object, and is often useful. Under
certain conditions, however, it has a tendency to cause the formation of
volatile chlorides with a consequent loss of metal.
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