quicker than they can be cut. What is more, the artificial
abrasives do not injure the lungs of the operatives like sandstone. The
output of artificial abrasives in the United States and Canada for 1917
was:

Tons Value
Silicon carbide 8,323 $1,074,152
Aluminum oxide 48,463 6,969,387

A new use for carborundum was found during the war when Uncle Sam
assumed the role of Jove as "cloud-compeller." Acting on carborundum
with chlorine--also, you remember, a product of electrical
dissolution--the chlorine displaces the carbon, forming silicon
tetra-chloride (SiCl_{4}), a colorless liquid resembling chloroform.
When this comes in contact with moist air it gives off thick, white
fumes, for water decomposes it, giving a white powder (silicon
hydroxide) and hydrochloric acid. If ammonia is present the acid will
unite with it, giving further white fumes of the salt, ammonium
chloride. So a mixture of two parts of silicon chloride with one part of
dry ammonia was used in the war to produce smoke-screens for the
concealment of the movements of troops, batteries and vessels or put in
shells so the outlook could see where they burst and so get the range.
Titanium tetra-chloride, a similar substance, proved 50 per cent. better
than silicon, but phosphorus--which also we get from the electric
furnace--was the most effective mistifier of all.

Before the introduction of the artificial abrasives fine grinding was
mostly done by emery, which is an impure form of aluminum oxide found in
nature. A purer form is made from the mineral bauxite by driving off its
combined water. Bauxite is the ore from which is made the pure aluminum
oxide used in the electric furnace for the production of metallic
aluminum. Formerly we imported a large part of our bauxite from France,
but when the war shut off this source we developed our domestic fields
in Arkansas, Alabama and Georgia, and these are now producing half a
million tons a year. Bauxite simply fused in the electric furnace makes
a better abrasive than the natural emery or corundum, and it is sold for
this purpose under the name of "aloxite," "alundum," "exolon," "lionite"
or "coralox." When the fused bauxite is worked up with a bonding
material into crucibles or muffles and baked in a kiln it forms the
alundum refractory ware. Since alundum is porous and not attacked by
acids it is used for filtering hot and corrosive liquids that w