224
EXPERIMENTS ON THE
The
experiment was repeated, the crucible being charged with iron, sugar
carbon, 5 per cent, manganese, 5 per cent, cobalt, 2 per cent, silicide
of carbon, boiled, and 2 per cent, iron sulphide added.
It
was also repeated with water instead of carbon dioxide snow. The result
of all these experiments was similar to the first. No diamond was found
in any part.
An
experiment which seemed to give practically instantaneous coohng was as
follows: A small carbon crucible containing iron, with traces of
silicon, aluminium, calcium, magnesia and sulphur, was floated on a
carbon block on a bath of mercury, all contained in a vessel exhausted
to 2 mm. absolute. The crucible was heated by an arc from an
upper carbon, the holder passing through a stuffing-box. When the
crucible was sufficiently hot and the contents carburised, the upper
carbon was thrust down, submerging the crucible under the mercury; the
coohng was almost explosive and instantaneous—the finely divided iron
and graphite on analysis yielded no diamond.
Extremely rapid cooling does not, therefore, seem to be a direct cause in the production of diamond.
Experiments at atmospheric pressure
A
convenient method of studying the effect of the association of other
elements with iron on a small scale uncontaminated by the vapours of a
furnace lining suggested itself, and a series of experiments was made
as follows: A deep iron dish was packed tightly with Acheson graphite
with a slight dimple in the centre to hold the ingot; above, graphite
was filled in loosely to a depth of half an inch covering the ingot. An
arc was struck by a carbon on to the ingot submerged in the loose
graphite. When the iron was well boiled the surrounding graphite with
the ingot in it was dug out entire and thrown into a bowl of mercury
covered with water.
The
results showed that, using ordinary mild steel, no diamond ever
occurred on analysis, but that a small percentage of silicon is
absolutely essential; small percentages of aluminium, magnesium,
calcium, one or all are important; sulphur, manganese, and cobalt
increase the yield, nickel appeared to be a disadvantage. An ahoy of
iron and 10 per cent, manganese, 10 per cent, cobalt, and 5 per cent,
silicon gave out much gas when cooled slowly, and on quick cooling in
water and mercury most of the spherules were burst and shredded.
Finally
about 1 to 3 per cent, of the other elements added to iron appeared to
give the best results and the spherules were not then burst.
An
experiment was made by letting the ingot remain in the bed till it had
quite set, hard enough to handle with the iron spoon, and then, cooled
in water and mercury. It gave a fair diamond residue.
