ORIGIN OF THE DIAMOND 365
tention
to the methods or method by which Nature created the compact and
beautiful crystal, and incidentally to enquire how and from what
source she obtained the necessary carbon. As to the means by which the
transformation was effected, they have succeeded so far that they can
make the crystals in microscopic size, and thereby illustrate in a
general way the larger methods of Nature; but whence she gathered the
supply of material for her furnaces is still an open question.
The
process of making diamonds as described by Sir William Crookes is to
select pure iron free from sulphur, silicon, phosphorus, etc., and pack
it in a carbon crucible with pure charcoal from sugar. This must be put
into the body of an electric furnace. After heating for a few minutes
to a temperature above 4,000 deg. C, at which heat the iron melts and
volatilizes, the current is stopped, and the crucible plunged into cold
water and held there until it sinks below a red heat.
The
outer layer of iron, solidified by the sudden cooling, holds the molten
interior in a rigid enclosure. The inner liquid expands as it
solidifies, thus creating an enormous pressure, under the stress of
which the dissolved carbon separates out in microscopic crystals which
though small are veritable diamonds.
Crookes
places the theoretical melting point of carbon at 4,400 deg. C.
absolute, and the melting pressure as 16.6 atmospheres. He found what
he believed to be diamonds, in residue obtained by exploding cordite in
closed steel cylinders. This meant a pressure of 8,000 atmospheres and
a temperature of about 5,400 deg. absolute.
Prof. Moissan first crystallized carbon artificially.
