His
method, which has been followed by other chemists, is almost identical
with that of Sir William Crookes, except that he plunged the
carbon-saturated iron into molten lead, to act as a binder for the
expansion by cooling of the interior mass.
Carbon
at a high temperature will seize on and combine with oxygen if it
exists in any compound, air or what not, with which it comes in
contact. It volatilizes at the ordinary pressure at about 3,600 deg. C.
and passes from a solid to a gaseous state without liquefying, but as
with other bodies of similar action, the addition of sufficient
pressure at the necessary temperature is thought to produce
liquefaction and with cooling, crystallization. The difficulties,
therefore, which scientists had to contend with were, first, to secure
the enormous temperature necessary to volatilize the carbon. This was
obtained by the development of the electrical furnace. Second, to hold
the carbon inert, and prevent its escape by combining with oxygen and
flying off as carbonic acid gas. As it was known that molten iron will
dissolve carbon, and that any excess of carbon beyond that which the
iron can hold will separate on cooling in the form of kish, which are
crystalline graphite plates, iron filings were used to enclose the
charcoal, and the whole was packed in a carbon crucible. The problem of
pressure was solved as described, by the expansion of a cooling
interior mass within the rigid enclosure of a suddenly cooled exterior
shell.
From
these experiments the most generally accepted hypothesis has been
advanced, that diamonds are a form of carbon produced by heat and
pressure, but how
