Experiments on the oxidation of alloys of iron when molten
Iron
was melted in a carbon crucible and highly carburised; when it had
somewhat cooled, the other elements were added, in small percentages of
aluminium, silicon, calcium, magnesium, manganese, iron sulphide,
collectively and in some cases singly; the crucible was then removed
from the furnace and superheated steam blown through a carbon tube into
the metal; energetic action took place and much heat was evolved; on
analysis, after destroying the graphite, a bulky transparent
crystalline residue remained.
With
aluminium alone the crystals were chiefly crystallised alumina, and
with the other elements the spinels and other crystals were produced;
all were transparent and colourless, but when chromium was added some
rounded crystals occurred resembhng pyrope. When submitted to sulphur
dioxide and carbon dioxide the result was the same, but less residue
was produced. Under the microscope there appeared to be a small
proportion of very small crystals like diamond; these burnt in oxygen.
When the bulky residue was placed in a test tube with the double
nitrate of silver and thallium, and the density adjusted so that a
diamond floated midway between the top and bottom, there collected into
its immediate neighbourhood after a time an amount of the small
crystals which was estimated to be about 5 per cent, of the total
residue.
One
prolonged treatment of hydrofluoric acid had no apparent effect on the
bulky residue, and it required so many treatments to destroy it that we
failed to isolate the very small particles whose size did not exceed
1/20 mm.; they were probably lost by flotation. These experiments were
repeated many times with the same result, but they merit further
investigation, with steam under high pressure and conditions
favourable to the formation of larger crystals.
Note. Marsden observed in silver the association of black diamond with crystalline alumina, silicide of carbon, etc., Roy. Soc. Proc. 1880.
Experiments in vacuo
The
presence of diamond in some meteorites suggested a series of
experiments under various degrees of vacuum up to the highest
obtainable.*
It
is probable that some meteoric matter may have been melted by collision
or ejected into space in a molten state and cooled by radiation, and
that under such conditions the absence, or diminution, of occluded
gases might be a factor conducive to the crystallisation of carbon.
One of the 4-inch diameter pressure moulds (Fig. 10) was used in a
* Also an impression suggested itself in 1907 that hydrogen had an adverse effect on the formation of diamond.
