This illuminated the ground on the darkest night sufficiently for the
airman to aim his bombs or to take photographs.
The addition of 5 or 10 per cent. of magnesium to aluminum gives an
alloy (magnalium) that is almost as light as aluminum and almost as
strong as steel. An alloy of 90 per cent. aluminum and 10 per cent.
calcium is lighter and harder than aluminum and more resistant to
corrosion. The latest German airplane, the "Junker," was made entirely
of duralumin. Even the wings were formed of corrugated sheets of this
alloy instead of the usual doped cotton-cloth. Duralumin is composed of
about 85 per cent. of aluminum, 5 per cent. of copper, 5 per cent. of
zinc and 2 per cent. of tin.
When platinum was first discovered it was so cheap that ingots of it
were gilded and sold as gold bricks to unwary purchasers. The Russian
Government used it as we use nickel, for making small coins. But this is
an exception to the rule that the demand creates the supply. Platinum is
really a "rare metal," not merely an unfamiliar one.
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