Since the monazite contains more cerium than thorium and the mantles made from it contain more thorium than cerium, there is a superfluity of cerium.  The manufacturers give away a pound of cerium salts with every purchase of a hundred pounds of thorium salts.  It annoyed Welsbach to see the cerium residues thrown away and accumulating around his mantle factory, so he set out to find some use for it.  He reduced the mixed earths to a metallic form and found that it gave off a shower of sparks when scratched.  An alloy of cerium with 30 or 35 per cent. of iron proved the best and was put on the market in the form of automatic lighters.  A big business was soon built up in Austria on the basis of this obscure chemical element rescued from the dump-heap.  The sale of the cerite lighters in France threatened to upset the finances of the republic, which derived large revenue from its monopoly of match-making, so the French Government imposed a tax upon every man who carried one.  American tourists who bought these lighters in Germany used to be much annoyed at being held up on the French frontier and compelled to take out a license.  During the war the cerium sparklers were much used in the trenches for lighting cigarettes, but—­as those who have seen “The Better ’Ole” will know—­they sometimes fail to strike fire.  Auer-metal or cerium-iron alloy was used in munitions to ignite hand grenades and to blazon the flight of trailer shells.  There are many other pyrophoric (light-producing) alloys, including steel, which our ancestors used with flint before matches and percussion caps were invented.

There are more than fifty metals known and not half of them have come into common use, so there is still plenty of room for the expansion of the science of metallurgy.  If the reader has not forgotten his arithmetic of permutations he can calculate how many different alloys may be formed by varying the combinations and proportions of these fifty.  We have seen how quickly elements formerly known only to chemists—­and to some of them known only by name—­have become indispensable in our daily life.  Any one of those still unutilized may be found to have peculiar properties that fit it for filling a long unfelt want in modern civilization.

Who, for instance, will find a use for gallium, the metal of France?  It was described in 1869 by Mendeleef in advance of its advent and has been known in person since 1875, but has not yet been set to work.  It is such a remarkable metal that it must be good for something.  If you saw it in a museum case on a cold day you might take it to be a piece of aluminum, but if the curator let you hold it in your hand—­which he won’t—­it would melt and run over the floor like mercury.  The melting point is 87 deg.  Fahr.  It might be used in thermometers for measuring temperatures above the boiling point of mercury were it not for the peculiar fact that gallium wets glass so it sticks to the side of the tube instead of forming a clear convex curve on top like mercury.