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ORIGIN OF THE DIAMOND 363
established
beyond question or doubt. But it was a form of carbon only. Graphite,
the other form in which it is found in Nature, to sight and touch
distinctly different, is nevertheless chemically the same. Though it
requires less heat, it combines with oxygen in the same way, the
resulting carbon dioxide showing that the graphitic carbon and the
oxygen consumed in uniting, exist without appreciable loss in the gas.
In comparative tests it has been shown that the diamond burns more
easily than foliated graphite, but compact graphite succumbs more
readily to heat than the diamond.
Some
experimenters claim that upon oxidation, the diamond leaves no residue
whatever. Streeter says that in experiments made by Professor Pepper
under his observation with about one hundred small stones, a very
small amount of bluish ash remained.
When
oxygen is supplied, diamonds burn slowly at about the temperature given
as that of molten silver. If air is excluded they withstand the heat at
which pig-iron melts, but at the temperature at which bar-iron melts,
while retaining their form, they become coated with graphite. M.
Moissan, using his electric furnace, found that the graphite resulting
from the partial burning of diamonds, assumed irregular crystalline
forms.
From
the various experiments made by a number of scientists, it appears that
diamonds at a very high temperature without access of oxygen swell up
and are converted into graphite. In a current of air they gradually
become smaller and finally disappear. If the supply of oxygen is
insufficient for perfect combustion, they become coated with graphitic
carbon and burn slowly. At a very high temperature in oxygen, the edges
of the
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