heated by a gas burner at the centre of its length to dull red. These yielded similar crystal plates.
Control experiments showed that no similar plates existed in the untreated grit.
It
was also found that the cast-iron turnings would not produce this
effect on a second heating unless they had been subjected to CO at
atmospheric pressure for some hours. Carbon monoxide, sulphur dioxide,
cyanogen, hydrogen, nitrogen, oxygen, nitric acid gas, chlorine,
ammonia, ammonium oxalate vapour, ammonium chloride, acetylene, or coal
gas, produced no plates.
These
plates resemble diamond very closely in appearance and form of
crystallisation, they do not polarise, and some have triangular
markings; they will not, however, burn in oxygen at 900° C, and are
completely destroyed by chlorine purified from oxygen and water vapour
at 1100° C.; their specific gravity is about 3-2, they are therefore
not diamond.
Note. Recent
experiments have shown that carbon monoxide passed over molten iron
sulphide and then over carborundum grit below red heat at atmospheric
pressure also produces these plates, and that if coal gas is
substituted for carbon monoxide no plates are formed. Also that only a
few of the grains produce plates.
The composition of the grains is
Carborundum ... ... ... 36-56
Iron oxide and alumina ... ... 44-09
Lime ... ... ... ... ... 10-45
Magnesia ... ... ... ... 5-57
Summary of experiments and conclusions
The
experiments have shown that all the hydrocarbons, chlorides of carbon,
and oxides of carbon tested, deposit amorphous carbon or graphite on a
carbon rod electrically heated at any pressure up to 4400 atmospheres,
and in a few experiments up to 6000 atmospheres; and that at 15,000
atmospheres carbon and graphite electrically heated are either directly
transformed into soft graphite or are first vaporised and then
condensed as such.
While
the experiment of rapidly compressing a mixture of acetylene and oxygen
with the production of temperatures much in excess of that necessary
to vaporise carbon, accompanied by a momentary pressure of about 15,000
atmospheres, confirms the conclusion that the negative results obtained
in the attempts to convert graphite into diamond by electrical heating
are not due to lack of temperature; on the other hand, the presence of
minute crystals in the molten layer of the steel of the end of the
barrel
