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PRECIOUS STONES.
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In a paper by A. Verneuil, in 1904, " On the Artificial Reproduction of the Ruby by Fusion,"1
he describes a new method devised by him that has proved highly
satisfacÂtory, some of the stones prepared weighing up to 15 carats and
measuring over 5 m.m. in diameter. The smaller stones are, however, the
best, being free from bubbles, which are unfortunately always present
in the larger ones, and at once indicate their origin.
M.
Verneuil found that one of the chief difficulties to overcome was
cooling; for if cooled too quickly the alumina becomes slaggy and an
enamel is produced. He invented a most ingenious piece of blow-pipe
apparatus, by means of which he could bring about the gradual fusing
and as gradual cooling. The blow-pipe and furnace-tube were made
vertically, and very finely powdered alumina containÂing a trace of
chromic oxide was fed into the tube through a sieve by means of a
series of regular taps controlled by an electro-magnet. This
arrangement causes the material to fall down the tube intermittently in
a series of thin layers. These layers gradually grow upwards in the
shape of a cone, the apex of which fuses on reaching a hot enough part
of the tube; the fused mass then extends in the form of a long
filament. This, on reaching a still hotter part of the furnace-tube
fuses into a spherical mass, which on cooling slowly, has all the
properties of the natural Ruby.
As the cost of producing artificial Rubies is very high, they are quite as dear as the natural stones.
Having described some of the methods of making Rubies,
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