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HOW TO MAKE SYNTHETIC DIAMONDS
solves
carbon, and on cooling, liberates it in the form of graphite. Moissan
discovered that several other metals, especially silver, have similar
properties. The quantity of carbon entering into solution increases
with the temperature.
For
the manufacturing of artificial diamonds the first necessity is to
select pure iron free from sulphur, silicon, phosphorus, etc., and to
pack it in a carbon crucible with the pure charcoal of some organic
substance such as sugar and starch. Moissan used such a mixture in a
furnace with 700 amperes and 40 volts. Beside graphite and diamonds
there may be formed black opaque carbon particles of a density from 3.0
to 3.5 and the hardness of diamonds. These are black diamonds or
carbonado. In fact comparatively few diamonds are transparent and
colorless and show crystalline structure. Besides these may be carbide
of silicon and corundum, arising from impurities in the material
employed. Graphite dissolves in hydrofluoric acid. Graphitic oxide may
be left.
Crookes
says Sir James Dewar placed a few small diamonds in a carbon tube,
and, maintaining a current of hydrogen to prevent oxidation, raised the
temperature of the tube in an electric furnace to that of the arc. In a
few minutes the diamond was transformed into graphite.
To
remove graphite after it is well washed allow it to soak in strong
hydrofluoric acid in the cold for two days, then in boiling acid. After
this treatment, hot sulfuric acid is again applied to remove the
fluorides. The residue is well washed and again treated with nitric
acid and potassium
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