t 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. Nowhere except in
the Urals is it found in quantity, and since it seems indispensable in
chemical and electrical appliances, the price has continually gone up.
Russia collapsed into chaos just when the war work made the heaviest
demand for platinum, so the governments had to put a stop to its use for
jewelry and photography. The "gold brick" scheme would now have to be
reversed, for gold is used as a cheaper metal to "adulterate" platinum.
All the members of the platinum family, formerly ignored, were pressed
into service, palladium, rhodium, osmium, iridium, and these, alloyed
with gold or silver, were employed more or less satisfactorily by the
dentist, chemist and electrician as substitutes for the platinum of
which they had been deprived. One of these alloys, composed of 20 per
cent. palladium and 80 per cent. gold, and bearing the telescoped name
of "palau" (palladium au-rum) makes very acceptable crucibles for the
laboratory and only costs half as much as platinum. "Rhotanium" is a
similar alloy recently introduced. The points of our gold pens are
tipped with an osmium-iridium alloy. It is a pity that this family of
noble metals is so restricted, for they are unsurpassed in tenacity and
incorruptibility. They could be of great service to the world in war and
peace. As the "Bad Child" says in his "Book of Beasts":

I shoot the hippopotamus with bullets made of platinum,
Because if I use leaden ones, his hide is sure to flatten 'em.

Along in the latter half of the last century chemists had begun to
perceive certain regularities and relationships among the various
elements, so they conceived the idea that some sort of a pigeon-hole
sc