ARTIFICIAL PRODUCTION OP DIAMOND 217
through
a central core (Fig. 2) small residues of diamond occasionally
occurred. A review of these experiments, however, indicates in most
cases an association with iron, whether introduced intentionally, or
present from the melting of the poles, or from other causes.
Experiments designed to melt carbon under pressure by
resistance heating
In
the attempts to melt carbon under pressure by this method (Fig. 3) heat
was applied for a duration of 5 seconds, sufficient in amount to melt
the graphite core six times over, with the result of only altering the
structure. Richard Threlfall independently came to the conclusion from
his experiments at about the same time, 1907, that under 100 tons per
square inch, graphite, electrically heated, remained graphite.
It
appeared, however, desirable further to investigate the possibility of
carbon losing its electrical conductivity when approaching its melting
point, as alleged by Ludwig and others, and of thus shunting the
current from itself on to the contiguous molten layers of the
insulating barrier surrounding it. There had, however, been no
indication of this having occurred, even momentarily; the evidence was
rather that the graphite core had been vaporised and condensed in the
surrounding parts of the charge, yet it was thought well to repeat the
experiment with rods of iron and tungsten embedded in the core, so that
should the temperature of volatilisation of the metals under a pressure
of 12,000 atmospheres exceed that necessary to liquefy carbon under the
same pressure, the presence of these metals might produce a different
result. No change, however, occurred, though in one experiment the
pressure was raised to 15,000 atmospheres.
Experiments designed to melt carbon under pressure by the rapid compression of flame
A
different mode of attack was then arranged, which would ensure that
carbon should be subjected to an extremely high temperature
concurrently with high pressure, obtained by the rapid compression of
the hottest possible flame, that of acetylene and oxygen, with a slight
excess of the former to provide the carbon.
The arrangement was as follows (Figs. 4 and 5):
A
very light piston made of tool steel was carefully fitted to the barrel
of a duck gun of 0-9 inch bore; the piston was fiat in front, lightened
out behind, and fitted with a cupped copper gas check ring, the cup
facing forward; the total travel of the piston was 36 inches. To the
muzzle of the gun was fitted a prolongation of the barrel, formed out
of a massive steel block, the joint being gastight. The end of the bore
in the block was
