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.  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 scheme might be devised in which the elements could be filed away in the order of their atomic weights so that one could see just how a certain element, known or unknown, would behave from merely observing its position in the series.  Mendeleef, a Russian chemist, devised the most ingenious of such systems called the “periodic law” and gave proof that there was something