graphite
in the centre was altered to large and very soft flakes. Neither the
graphite nor the magnesium carbide contained any hard crystalline
carbon.
Similar
experiments were tried with carbon rods surrounded by silica, and as a
guide to the temperature reached, current was turned on of just
sufficient voltage to convert the rod to graphite; the mould was then
set up afresh and double the voltage applied, when the rod was
vaporised and disseminated throughout the molten silica, principally in
the form of graphite of very small grain, very little silicon and still
less silicide of carbon being formed.
Another
series of experiments has been made to investigate the behaviour of
vaporised carbon under fluid or gaseous pressures of about 30 tons per
square inch. The general arrangement of the mould consisted of a
central carbon rod with a lining of marble; in some cases the space
between the rod and marble was packed with coarsely powdered charcoal.
Several
compounds of carbon were treated, perhaps the most interesting being
carbon dioxide. The liquid was run into the mould and a pressure of 30
tons per square inch applied. It was found that its volume diminished
to about 80 per cent., due to its compressibility. Current was then
passed through the rod, and the liquid must then have existed as
gaseous carbon monoxide in the hotter zones.
When
cooled, the liquid and gas were allowed to escape; a sample of this gas
on analysis was found to contain 95 per cent, of carbon monoxide and 3
per cent, carbon dioxide, the residue consisting apparently of nitrogen.
As
the pressure of 30 tons was maintained throughout the experiment, it
would seem that the compressibility of carbon monoxide diminishes
rapidly at such high pressures, but this experiment will be repeated
and will form the subject of a subsequent paper on the compressibility
of liquids and gases. Part of the central carbon was converted to
graphite, and in one place there was found a nest of woolly deposited
carbon, showing that under a pressure of 30 tons per square inch carbon
vaporised in carbon monoxide is deposited in the form of amorphous
carbon.
Conclusions
From
these experiments several hundred samples have been carefully analysed.
In none of the experiments designed to melt or vaporise carbon under
pressure has the residue contained more than a suspicion of black or
transparent diamond.
In
no experiment we have made has there been any sign of the carbon
becoming a non-conductor, and the impression derived is undoubtedly
that soft crystals of graphite are the resulting stable form of carbon
after heating to very high temperatures.
