glycerin compounds of these acids (known as olein, stearin, etc.), as
well as various others of a similar sort. If you will set a bottle of
salad oil in the ice-box you will see it separate into two parts. The
white, crystalline solid that separates out is largely stearin. The part
that remains liquid is largely olein. You might separate them by
filtering it cold and if then you tried to sell the two products you
would find that the hard fat would bring a higher price than the oil,
either for food or soap. If you tried to keep them you would find that
the hard fat kept neutral and "sweet" longer than the other. You may
remember that the perfumes (as well as their odorous opposites) were
mostly unsaturated compounds. So we find that it is the free and
unsaturated fatty acids that cause butter and oil to become rank and
rancid.

Obviously, then, we could make money if we could turn soft, unsaturated
fats like olein into hard, saturated fats like stearin. Referring to the
symbols we see that all that is needed to effect the change is to get
the former to unite with hydrogen. This requires a little coaxing. The
coaxer is called a catalyst. A catalyst, as I have previously explained,
is a substance that by its mere presence causes the union of two other
substances that might otherwise remain separate. For that reason the
catalyst is referred to as "a chemical parson." Finely divided metals
have a strong catalytic action. Platinum sponge is excellent but too
expensive. So in this case nickel is used. A nickel salt mixed with
charcoal or pumice is reduced to the metallic state by heating in a
current of hydrogen. Then it is dropped into the tank of oil and
hydrogen gas is blown through. The hydrogen may be obtained by splitting
water into its two components, hydrogen and oxygen, by means of the
electrical current, or by passing steam over spongy iron which takes out
the oxygen. The stream of hydrogen blown through the hot oil converts