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CHEMICAL PROPERTIES OF MINERALS. 115
like
fluorine, acting on the glass. It may next be tried in an open tube of
glass, through which a more or less strong current of air passes
according to the inclination at which the tube is held, so that
volatile oxides or acids may be formed ; and in this way the chief
combinations of sulphur, selenium, tellurium, and arsenic are detected.
On charcoal, in the reducing flame, arsenic, and in the oxidating
flame, selenium or sulphur, are shown by their peculiar odor; antimony,
zinc, lead, and bismuth leave a mark or colored ring on the charcoal;
and other oxides and sul-phurcts are reduced to the pure metal. On
charcoal or in the platinum pincers the fusibility of minerals is
tested, and some other phenomena should be observed—as whether they
intumesce (bubble up), effervesce, give out fumes, become shining, or
impart a color to the flame. The color is seen when the assay is heated
at the point of the inner flame, and is—
Reddish-yellow, from soda and its "salts ;
Violet, from potash and most of its salts ;
Red, from lithia, strontia, and lime ;
Green, from baryta, phosphoric acid, boracic acid, molybdic acid,
copper oxide, and tellurium oxide ;.
Blue, from chloride of copper, bromide of copper, selenium, arsenic,
antimony, and lead.
The
fusibility, or ease with which a mineral is melted, should also be
observed; and to render this character more precise, Von Kobell has
proposed this scale:—(1.) Antimony glance, which melts readily in the
mere candle flame; (2.) Xatroiite, which in fine needles also melts in
the candle flame, and in large pieces readily before the blowpipe; (3.)
Almandine (garnet from Zillerthal), which does not melt in the candle
flame even in fine splinters, but in large pieces before the blowpipe;
(4.) Strahlstein (hornblende from Zillerthal) melts with some
difficulty, but still more readily than (5.) Orthoclase (or adularia
felspar); and (6.) Bron-
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