270 Science and Human Welfare
Two of the most useful of all the metals exist on the earth
in fantastic abundance—aluminum in the clay underfoot
and magnesium in sea water. But so complicated is the job
of extraction that we have known these metals in quantity
for only a generation. Today, in airplanes and bombs of war,
these lightweights shake the world. Aluminum, about one-
third as heavy as iron, and magnesium, less than one-fourth
of iron’s weight, are chiefly responsible for the wonderfully
low ratio of weight to power in the airplane engines.
Aluminum owes its origin, in its pure form, to the per-
sistence and genius of a young American named Charles
Martin Hall who, in 1886, discovered that when aluminum,
purified from bauxite, was dissolved in a molten bath of
cryolite, aluminum could be obtained by the electrolysis of
this fused mass. Strategically our chief concern was the sup-
ply of cryolite and the production capacity of alumina
plants. Fortunately, for this program, President Wilson was
farsighted in pushing construction of enormous water power
projects along the Tennessee and Columbia rivers. The
aluminum industry is now using artificial cryolite. Aluminum
can be extracted from alunite and this is now being done by
a newly developed process.
Some twenty years ago a German scientist discovered that
if aluminum were mixed with about four per cent of copper,
one-half of a per cent each of magnesium and manganese,
and if the resulting alloy were heated, quenched, and then
allowed to age for several days—this light and relatively
soft, weak metal increased its strength fourfold. This alloy
is “Duralumin.” New alloys, typified by 25S and 24S, have
been developed which combine easy forgeability with good
strength. Many of the alloys are quite vulnerable to corro-
sion. Pure aluminum, on the other hand, is highly resistant
to corrosion since it immediately acquires a virtually invis-