ould eat
up filter-paper. Carborundum or crystolon is also made up into
refractory ware for high temperature work. When the fused mass of the
carborundum furnace is broken up there is found surrounding the
carborundum core a similar substance though not quite so hard and
infusible, known as "carborundum sand" or "siloxicon." This is mixed
with fireclay and used for furnace linings.

Many new forms of refractories have come into use to meet the demands of
the new high temperature work. The essentials are that it should not
melt or crumble at high heat and should not expand and contract greatly
under changes of temperature (low coefficient of thermal expansion).
Whether it is desirable that it should heat through readily or slowly
(coefficient of thermal conductivity) depends on whether it is wanted as
a crucible or as a furnace lining. Lime (calcium oxide) fuses only at
the highest heat of the electric furnace, but it breaks down into dust.
Magnesia (magnesium oxide) is better and is most extensively employed.
For every ton of steel produced five pounds of magnesite is needed.
Formerly we imported 90 per cent. of our supply from Austria, but now we
get it from California and Washington. In 1913 the American production
of magnesite was only 9600 tons. In 1918 it was 225,000. Zirconia
(zirconium oxide) is still more refractory and in spite of its greater
cost zirkite is coming into use as a lining for electric furnaces.

Silicon is next to oxygen the commonest element in the world. It forms a
quarter of the earth's crust, yet it is unfamiliar to most of us. That
is because it is always found combined with oxygen in the form of silica
as quartz crystal or sand. This used to be considered too refractory to
be blown but is found to be easily manipulable at the high temperatures
now at the command of the glass-blower. So the chemist rejoices in
flasks that he can heat red hot in the Bunsen burner and then plunge
into ice water without breaking, and the cook can bake and serve in a
dish of "pyrex," which is 80 per cent. silica.

At the beginning of the twentieth century minute specimens of silicon
were sold as laboratory curiosities at the price of $100 an ounce. Two
years later it was turned out by the barrelful at Niagara as an
accidental by-product and could not find a market at ten cents a pound.
Silicon from the electric furnace appears in the form of hard,
glittering metallic crystals.

An alloy of iron and silicon, f