rify the metal and thus to increase its tensile
strength. Like titanium, it is added chiefly for its curative effect
rather than as a useful ingredient. On an average 4 pounds of 50 to 55
per cent ferrosilicon are used in the United States for each ton of
steel produced. A higher grade of ferrosilicon (80 to 85 per cent) is
used for certain special steels, and during the war considerable
quantities were used in making hydrogen gas for balloons. Lower grades
(10 to 15 per cent silicon) are practically a high silicon pig iron.

Silica has an important use in the form of silica brick or "ganister"
for lining furnaces and converters in which acid slags are formed. For
this purpose siliceous rocks, chiefly quartzites and sandstones, are
ground up, mixed with lime as a binder, and fused and pressed into
bricks and shapes. For the most satisfactory results the rock should
contain 96 per cent or more of silica, and very little of the alkali
materials, which increase the fusibility.

In addition to its applications to the iron and steel industry, silica
finds an almost universal use in a wide variety of structural and
manufacturing operations. The extensive use of sand and gravel--composed
chiefly of silica--for road materials and railway ballast is well known.
In construction work silica is used in the form of stone, sand-lime
brick, cement, mortar, concrete, etc. Large quantities of sand, or
silica, are used for molds in foundries, for abrasives, for the
manufacture of glass, for filters, and for a great variety of other
purposes which readily suggest themselves (see pp. 84, 267).

For most uses of silica there are local supplies available. For certain
purposes requiring material of a particular chemical composition or
texture, however, satisfactory deposits are known in only a few places.
For example, the material for silica refractories is obtained in the
United States chiefly from certain regions in Pennsylvania, Missouri,
and Wisconsin. The United States has ample domestic supplies of silica
for practically all requirements.

Ferrosilicon of the higher grades is manufactured principally in
electric furnaces at Niagara Falls. The capacity is ample to meet all
demands, but cheap ferrosilicon from Canada also enters United States
markets.

GEOLOGIC FEATURES

Silicon and oxygen, making up the compound silica, are the two most
abundant elements in the earth's crust, and quartz (SiO_2) is a very
abundant mineral. The pr