saturated with oil, soft crystals of graphite exuded from specimens that had been kept for some weeks.
No.
2. Pure hydrated alumina, carbonate and oxide of magnesia, and lime all
rapidly destroyed the carbon rod by combining with it, the hydrated
alumina forming large volumes of gas of which it appeared to be a
constituent. On account of the great diminution of bulk, no analysis
was made; the gas issued from the mould explosively at from 10 to 12
tons per square inch. The alumina was found in a crystalline crust,
like sugar, around where the rod had been. Hardness that of corundum,
almost translucent.
No.
3. The following is the most interesting experiment of the series: On
the bottom of the mould was a layer of slaked lime about 1/4 inch
thick, over this silver sand 2 inches, then another layer of lime of
the same thickness as the former, finally a layer of coke dust, and
then the plunger. With a pressure of from 5 to 30 tons per square inch
in the mould, and the carbon of from 1/4 to 5/16 inch diameter, currents of from 200 to 300 amperes were passed.
In
from 10 to 30 minutes the current was generally interrupted by the
breaking or fusing of the rod, or by the action of the lime in
dissolving it at the top or bottom. On opening the mould when it had
cooled a little, the silica usually appeared to have melted to an
egg-shaped mass, and mixed somewhat at the ends with the lime; the
surface of the carbon appeared acted on, and sometimes pitted and
crystalline in places; silica adhered to the surface, and beneath, when
viewed under the microscope, appeared a globular cauliflower-like
formation of a yellowish colour, resembling some specimens of "bort"'.*
After
several days' immersion in concentrated hydrofluoric acid, this
formation remained partly adherent to the carbon; on the surface of the
carbon was a layer or skin about 1/64 of an inch thick of great
hardness, on the outside grey, the fracture greyer than the carbon, but
having a shining coke-like appearance under the microscope.
The
powder scraped off the surface of the rod has great hardness, and will
cut rock crystal when applied with a piece of metal faster than emery
powder. It has, under the microscope, the appearance of bort, the
minute particles seem to cling together; they are not transparent as a
rule, and though some such particles are found among them, it is not
clear that such are hard.
When
a piece of the skin has been rubbed against a diamond or other hard
body, the projecting or hard portions have a glossy coke-like
appearance.
A
piece of the skin will continue to scratch rock crystal for some time
without losing its edge. It will scratch ruby, and when rubbed for some
* The bort-like powder is not acted on by hydrofluoric and nitric acids mixed.
