common
laws which govern other substances, and can be made volatile and
fusible under certain conditions. He has demonstrated that the
temperature necessary to volatilize pure carbon is about 36000
C, and that it passes into the gaseous state without liquefying, and he
infers that, if sufficient pressure were applied with the high
temperature, liquid carbon would be produced which upon cooling would
crystallize in diamonds. For this product the absence of oxygen is
absolutely necessary, as the carbon would readily unite with it in the
form of carbonic acid. It is a well-known fact that iron when melted
dissolves carbon, and while Moissan discovered that other metals effect
this dissolution, he found that iron was the best solvent.
Sir
William Crookes went through the process of producing diamonds before
the eyes of his audience, but was only able to show them the result of
this experiment by reproducing a lantern slide of microscopical
diamonds which he had made in the same way previously, for it takes a
fortnight to separate them from the iron and other substances in which
they are embedded. The scientific principle upon which this experiment
rests, according to Sir William Crookes, is that molten iron absorbs
carbon, and as iron increases in volume as it passes from the liquid to
the solid state, if the outer crust of the iron is suddenly cooled and
the centre remains in a liquid state, the enormous pressure caused by
its expanding while cooling affords the two factors necessary for the
crystallization of the diamond — heat and pressure.
Authorities
differ somewhat as to the exact moment when molten iron expands on
cooling, but it is the generally accepted theory that expansion takes
place at the moment of solidification. It is also a well-known fact
that shrinkage or contraction takes place as the solidified metal
cools. It is therefore possible to obtain enormous pressure in the
molten centre of a casting by the contraction of the outer shell which
has been rapidly cooled and the expansion of the inner mass just as it
begins to solidify.1
1
American Society Mechanical Engineers, Vol. XVIII, pp. 419 and 431.
American Institute of Mining Engineers, Vol. XVII, 126 and 1015.
