364 THE DIAMOND
sharp
angles are first rounded, the crystals split, lose their transparency
and luster, and are eventually entirely consumed. During the process
of combustion, successive black spots appear on the surface of the
crystal and disappear. It also gives out bright red sparks. If the
process is suspended, the diamond at once ceases to burn and shows a
leaden surface. The inference is, that the heat first transforms the
carbon of the surface to the graphitic form, which then combines with
the oxygen and passes off as carbon dioxide, or carbonic acid gas.
Many
interesting illustrations of the chemistry of diamonds have been given
by scientists in their experiments. It has been shown that if one is
sufficiently heated and then plunged into liquid oxygen, it burns
brightly, and the carbonic acid formed by the combustion, becomes in
the low temperature of the condensed oxygen, a solid which appears like
snow. The gas from a burning diamond passed through clear limewater
will cause it to become milky, and finally, an insoluble compound,
calcium carbonate, will be thrown down. By filling a flask with oxygen
and limewater, and placing within it a diamond held by a coil of
platinum wire joined to the wires of a galvanic battery passing through
the stopper, the entire process can be seen upon turning on the
current; the platinum wire will become white hot, the diamond will
burn, and the carbon dioxide created, will act upon the calcium
hydroxide of lime. At an extremely high temperature, M. Moissan
succeeded in volatilizing carbon.
Having settled definitely the question of the composition of the diamond, scientists next turned their at-
