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THE ARTIFICIAL PRODUCTION OF DIAMOND 215
mersed
in liquids at pressures up to 2200 atmospheres, and where the
liquids—benzene, paraffin, treacle, chloride and bisulphide of
carbon—were found to yield deposits of amorphous carbon.
In
my paper of 1907 allusion was made to experiments in liquids at a
pressure of 4400 atmospheres, and to the distillation of carbon in
carbon monoxide and dioxide at this pressure with similar results, also
to an attempt to melt carbon at pressures up to 15,000 atmospheres,
which produced soft graphite, and an experiment where a carbon
crucible, containing iron previously heated and carburised in the
electric furnace, was quickly transferred to a steel die, and while
molten and during cooling subjected to a pressure of 11,200
atmospheres, the analyses showing less crystalline residue than if the
crucible had been cooled in water.
It
was also emphasised that the pressure of 11,200 atmospheres must be
greater than could be produced in the interior of a spheroidal mass of
cast iron when suddenly cooled, and that the inference from these
experiments was that mechanical pressure is not the cause of the
production of diamond in rapidly cooled iron, as had been supposed by
Moissan. This conclusion appears to us in the light of our more recent
experiments to be one of great importance, and it will be further
discussed in this paper.
It
may be well to state that, in order to facilitate a clearer view of the
bearing of each experiment on the subject, they are not placed always
in chronological order. The difficulty of ensuring satisfactory
experiments and the elusive character of the analyses must be the
excuse for the random character of some of the former. The great
majority of the experiments were failures as regards results, but a few
have given information that was scarcely anticipated when they were
devised.
Several
thousand experiments have been made and a much greater number of
analyses, generally following the methods of Moissan and Crookes; the
more important experiments are described at some length, and in most
cases are typical of groups or repetitions of the same experiment with
small variations.
The
selection has been chiefly determined by their bearing on the general
trend of the results of our own work and the work of others.
Those
who are familiar with analyses for the detection and isolation of
minute particles of diamond will know of the tendency of such particles
to float, and to become lost in the frequent washings. To diminish the
risk of arriving at erroneous conclusions the analyses of the more
important experiments have generally been repeated several times.
Experiments under high pressure
In
the experiments designed to test chemical reactions under high
pressure, where the charge was heated by passing an electric current
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