enable the new struggling industries to exist, and
to permit of development of adequate home supplies. Such tariffs might
be beneficial to these particular domestic industries if wisely planned;
but also, in view of the limited amounts of these particular ores in
this country, their general low grade, and the high cost of mining,
tariffs might very probably hasten exhaustion of our limited supplies
and might handicap our metallurgical industries both in efficiency and
cost (see pp. 365-366, 393-394).

IRON ORES

ECONOMIC FEATURES

=Technical and commercial factors determining use of iron ore minerals.=
Popularly, an iron ore is an iron ore, and there is little realization
of its really great complexity of composition and the difficulty of
determining what is or is not a commercial ore. Percentage of iron is of
course an important factor; but an ore in which the iron is in the
mineral hematite is more valuable than one with an equivalent percentage
of iron which is in the form of magnetite. Substances present in the ore
in minor quantities, such as phosphorus, sulphur, and titanium, have a
tendency to make the iron product brittle, either when it is cold or
when it is being made, so that excessive amounts of these substances may
disqualify an ore. Excessive quantities of silica, lime, or magnesia may
make the ore undesirable. Where an acid substance, like silica, is
balanced by basic constituents like lime and magnesia, considerable
amounts of both may be used. Excessive moisture content may spoil an ore
because of the amount of heat necessary to eliminate it in smelting.

The metallurgical processes of the iron and steel industry are
essentially adapted to the principal grades of ore available. The
cheapest of the steel-making processes, called the acid Bessemer
process, requires a very low-phosphorus ore (usually below .050 per cent
in the United States and below .030 per cent in England.) The basic
open-hearth processes, making two-thirds of the steel in the United
States, allow higher percentages of phosphorus, but not unlimited
amounts. The basic Bessemer (Thomas) process, used for the "minette"
ores of western Europe and the Swedish magnetites, may use an ore with
any amount of phosphorus over 1.5 per cent. The phosphatic slag from
this process is used as fertilizer. The supply of low-phosphorus
Bessemer ore in the United States is at present limited as compared with
that of the non-Bessemer ores, with the