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80 PRECIOUS STONES.
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of
discussion. What does the Diamond consist of? How was it formed ? Can
it be made artificially ? Thanks to the rapid progress in scientific
research, all these questions have been answered, perhaps not quite so
successfully as we desire, but still in a satisfactory manner.
The
composition of the Diamond was early observed by Gassiot and Berzelius;
and Lavosier, in 1772, showed that if heated to a high enough
temperature (about 800° C. according to Moissan) it burned away,
producing by combination with the oxygen of the air that heavy noxious
gas, carbon anhydride (carbonic acid), the after-damp or choke-damp of
coal pit explosions. Smithson Tennant, in 1779, proved that carbonic
acid was the only product of the Diamond's combustion. This was
verified by Davy in 1814, who was the first to prove that it consisted
almost wholly of pure carbon, the residue after combustion being only
0'2 to 0*05 per cent, of an ash made up of silica and oxide of iron.
One of the earliest theories of the Diamond's origin was propounded by
Sir Isaac Newton, who stated that it is in all probability " an
unctuous substance coagulated." This theory, no doubt, was based upon
its high refractive properties, ordinary gum arabic being not at all
unlike rough Diamonds. A similar theory put forward by Sir David
Brewster was that it owed its origin to the vital processes of plants,
and was at one time viscous, like resin.
For
a considerable time theory held first place and practical experiments
gave no satisfactory results. Theory after theory followed each other
in rapid succession from such men as D'Orbigny, Wohler, Liebig,
Berthelot, Bischof, C. C. Von Leonhard, Parrot, Carvill Lewis, Wilson,
Goppert
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