ARTIFICIAL PRODUCTION OP GEMS. 143
The
mass was brought slowly to a white-heat temperature, and kept from
twenty-four to thirty hours in that condition. The boracic acid begins
to evaporate during the last five hours.
The emerald was obtained artificially by a mixture of
Mr.
Daubrée has produced artificially the oxide of tin, by passing through
a heated porcelain tube two currents of the vapors of the perchloride
of tin and water, by which a double decomposition was effected, so that
in the interior of the porcelain tube small crystals of oxide of tin
were deposited, and hydrochloric acid gas passed off in the form of
vapor. The crystals of tin were deposited at the orifice of the
porcelain tube, where the temperature was scarcely 300°, while no
crystals were deposited in the hottest part ; the crystals of tin
scratched glass easily, were infusible, and were, not affected by
acids, and had a specific gravity of 6-72.
The
latest discoveries of Mr. Daubrée have brought to light many important
facts in regard to the formation of rocks which contain crystalline
substances, differing widely in their fusibility. By the action of
chloride of silicium at red heat, and vapor on many bases which enter
into various rocks he obtains in exchange, by decomposition, chlorine
bases and free silica (silicic acid), which appears as quartz in
crystals ; if he desires an action of the chloride of silicium on
chalk, magnesia, alumina, or glucia, he obtains crystals of quartz,
wallastonite, peridote, and disthene ; for the purpose of obtaining
double silicates, he not only adds the bases for silicifying in proper
proportions, but also in
