subjected
to high gaseous pressures of carbon monoxide, carbon dioxide, and
hydrogen appears to be connected with the other experiments bearing
upon the inclusion of gases in metal as a factor in the production of
diamond.
The
experiment of firing a high velocity steel bullet with cupped nose
through vaporising carbon into a hole in a block of steel has tested
the effect of a momentary pressure of about 300,000 atmospheres on
carbon initially near its melting point, and probably raised by
adiabatic compression by another 1000° C.
The
fact that only a very few minute crystals resembling diamond were
produced (probably from the iron) raises the question as to whether the
duration of the pressure is sufficient to start a transformation of
graphite to diamond which can be detected by analysis. We have distinct
evidence that, with iron as the matrix, the time is sufficient to form
very small crystals which can be identified with some certainty. It
therefore seems reasonable to conclude that there was no incipient
transformation in bulk, and that however long the pressure of 300,000
atmospheres were applied, it is extremely doubtful if any change would
occur.
The
pressure of 300,000 atmospheres is between one quarter and one half
that obtaining at the centre of the Earth, but vastly greater pressures
exist at the centre of the larger stars, and are produced by the
collision of large bodies in space; these pressures are many thousands
of times greater, and whether they would effect the change it is
impossible to predict. On the other hand, a heating effect on large
masses of iron might be produced by collisions, and owing to the heat
generated by adiabatic compression of the central portions, some of the
mass would be melted and subsequently cooled on release of the
pressure, so that if heating and cooling under pressure are alone
necessary for the production of diamond large stones might result.
These considerations, though of interest as bearing upon the presence
of diamonds in meteorites and also indicating a possible origin of
natural diamond, are of no practical value to us because the pressures
required are entirely beyond our reach. There are, however, other
considerations arising out of the experiments of Marsden, Moissan, and
Crookes, as well as our own, which seem to give some hope of solutions
of the problem at issue which lie within the means at our disposal.
A
repetition has been made of many of the experiments in which diamond is
claimed to have been produced. These have given negative results in all
cases except where iron has played a part, as for instance with
olivine, when being partly reduced by carbon or a reducing flame, small
spherules of iron are produced and may, if the mass is quickly cooled,
be found to contain diamond.
The repetition of Moissan's experiments under a variety of conditions
