By means of these new metals armor plate has been made invulnerable—­except to projectiles pointed with similar material.  Flying has been made possible through engines weighing no more than two pounds per horse power.  The cylinders of combustion engines and the casing of cannon have been made to withstand the unprecedented pressure and corrosive action of the fiery gases evolved within.  Castings are made so hard that they cannot be cut—­save with tools of the same sort.  In the high-speed tools now used 20 or 30 per cent, of the iron is displaced by other ingredients; for example, tungsten from 14 to 25 per cent., chromium from 2 to 7 per cent., vanadium from 1/2 to 1-1/2 per cent., carbon from 6 to 8 per cent., with perhaps cobalt up to 4 per cent.  Molybdenum or uranium may replace part of the tungsten.

Some of the newer alloys for high-speed tools contain no iron at all.  That which bears the poetic name of star-stone, stellite, is composed of chromium, cobalt and tungsten in varying proportions.  Stellite keeps a hard cutting edge and gets tougher as it gets hotter.  It is very hard and as good for jewelry as platinum except that it is not so expensive.  Cooperite, its rival, is an alloy of nickel and zirconium, stronger, lighter and cheaper than stellite.

Before the war nearly half of the world’s supply of tungsten ore (wolframite) came from Burma.  But although Burma had belonged to the British for a hundred years they had not developed its mineral resources and the tungsten trade was monopolized by the Germans.  All the ore was shipped to Germany and the British Admiralty was content to buy from the Germans what tungsten was needed for armor plate and heavy guns.  When the war broke out the British had the ore supply, but were unable at first to work it because they were not familiar with the processes.  Germany, being short of tungsten, had to sneak over a little from Baltimore in the submarine Deutschland.  In the United States before the war tungsten ore was selling at $6.50 a unit, but by the beginning of 1916 it had jumped to $85 a unit.  A unit is 1 per cent. of tungsten trioxide to the ton, that is, twenty pounds.  Boulder County, Colorado, and San Bernardino, California, then had mining booms, reminding one of older times.  Between May and December, 1918, there was manufactured in the United States more than 45,500,000 pounds of tungsten steel containing some 8,000,000 pounds of tungsten.

If tungsten ores were more abundant and the metal more easily manipulated, it would displace steel for many purposes.  It is harder than steel or even quartz.  It never rusts and is insoluble in acids.  Its expansion by heat is one-third that of iron.  It is more than twice as heavy as iron and its melting point is twice as high.  Its electrical resistance is half that of iron and its tensile strength is a third greater than the strongest steel.  It can be worked into wire .0002 of an inch in diameter, almost too thin to be seen, but as strong as copper wire ten times the size.