e of
iron, particularly because it is susceptible of magnetic separation, a
process which as yet is only in its infancy. Containing, as it does, a
larger percentage of iron than any other source from which the metal
is commercially extracted, its employment as an ore results in great
economy of fuel, as well as a reduction in the proportionate costs of
transport. When ores of iron require to be brought from oversea
places, it is obvious that those which will concentrate to the purest
product possible, and which are in other respects specially applicable
to the production of grades of steel of exceptional tensile strength,
will have the preference.

Magnetic concentration, or the separation of an ore from the waste
gangue by the attraction of powerful electro-magnets, must therefore
occupy a much more prominent place in the metallurgy of the future
than it has in that of the past. Not only may ironstone containing
magnetite be separated from other material, but several important
minerals acquire the property of becoming magnetic when subjected to
the operation of roasting, sometimes through a sulphide being
converted into a magnetic oxide.

By the use of powerful electro-magnets, the poles of which are brought
to a point or to a nearly sharp knife-edge, the intensity of the
magnetic field can be so enormously increased that even minerals which
are only feebly magnetic can readily be separated by being lifted away
from the non-magnetic material. In some systems the crushed ore is
simply permitted to fall in a continuous stream through a strong
magnetic field, and the magnetic particles are diverted out of the
vertical in their descent by the operation of the magnets.

Nor is it only those minerals that actually become themselves magnetic
on being roasted which can be so differentiated from the material with
which they are associated as to be amenable to magnetic separation.
Even differences in hygroscopic properties--that is to say, in the
degree of avidity with which a mineral takes up moisture from the
atmosphere--may be made available for the purpose of effecting a
commercially valuable separation. This is especially the case with
some complex ores in which one constituent, on being roasted, acquires
a much greater hygroscopic power than the others, the grains of the
crushed and roasted ore becoming damp and sticky while those of the
other minerals remain comparatively dry. By mixing with an ore of this
kind--after