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216 Science and Human Welfare

Certain finite properties in steels are gained by the addi-
tion of the alloying elements. The effects of some have been
discussed. Vanadium imparts toughness to steel; selenium
gives free-cutting characteristics; nitrogen leads to grain re-
finement; thorium, titanium and Columbian inhibit carbon
precipitation; sulphur gives better machining properties and
zirconium is added to hold the sulphur.

Mercury, as fulminate in shells, touches off the thunder of
high explosives and the fury of incendiaries. It is used in the
anti-fouling paints to keep barnacles off of ships; in fluo-
rescent lighting; and for many other purposes. One General
Electric mercury boiler, supplying mercury vapor to drive a
20,000 kilowatt generator, carries 270,000 pounds of mercury
in its system. Sodium metal is added to the mercury to give
better heat transfer, and zirconium is added to retard the
solution of the boiler iron by the mercury. It should be in-
teresting to note that the mercury-vapor condensers are
really steam boilers, operating on a lower temperature plane.

Already concentration of low-grade ores has been men-
tioned. One ingenious process, flotation, has added many
so-called “worthless deposits” to our natural supplies. Flota-
tion is a process whereby the grains of one or more minerals,
or chemical compounds, in a pulp or slurry, are selectively
caused to rise to the surface by the action of bubbles of air.
The grains are caught in a froth, formed upon the surface of
the liquid, and are removed with the froth, while the grains
which do not rise remain in the slurry and are drawn off at
the bottom. Chemical collectors, frothers, depressers, and
deflocculating agents are added to increase the efficiency of
the separation.

In the Minnesota district a mixture of oleic acid with pine
oil, modified by sodium silicate with sodium carbonate as a
protector, suffices to give excellent concentration of man-

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