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 the linoleic acid to oleic and then the oleic into stearic.  If you figured up the weights from the symbols given above you would find that it takes about one pound of hydrogen to convert a hundred pounds of olein to stearin and the cost is only about one cent a pound.  The nickel is unchanged and is easily separated.  A trace of nickel may remain in the product, but as it is very much less than the amount dissolved when food is cooked in nickel-plated vessels it cannot be regarded as harmful.

Even more unsaturated fats may be hydrogenated.  Fish oil has hitherto been almost unusable because of its powerful and persistent odor.  This is chiefly due to a fatty acid which properly bears the uneuphonious name of clupanodonic acid and has the composition of C_{18}H_{28}O_{2}.  By comparing this with the symbol of the odorless stearic acid, C_{18}H_{36}O_{2}, you will see that all the rank fish oil lacks to make it respectable is eight hydrogen atoms.  A Japanese chemist, Tsujimoto, has discovered how to add them and now the reformed fish oil under the names of “talgol” and “candelite” serves for lubricant and even enters higher circles as a soap or food.

This process of hardening fats by hydrogenation resulted from the experiments of a French chemist, Professor Sabatier of Toulouse, in the last years of the last century, but, as in many other cases, the Germans were the first to take it up and profit by it.  Before the war the copra or coconut oil from the British Asiatic colonies of India, Ceylon and Malaya went to Germany at the rate of $15,000,000 a year.  The palm kernels grown in British West Africa were shipped, not to Liverpool, but to Hamburg, $19,000,000 worth annually.  Here the oil was pressed out and used for margarin and the residual cake used for feeding cows produced butter or for feeding hogs produced lard.  Half of the copra raised in the British possessions was sent to Germany and half of the oil from it was resold to the British margarin candle and soap makers at a handsome profit.  The British chemists were not blind to this, but they could do nothing, first because the English politician was wedded to free trade, second, because the English farmer would not use oil cake for his stock.  France was in a similar situation.  Marseilles produced 15,500,000 gallons of oil from peanuts grown largely in the French African colonies—­but shipped the oil-cake on to Hamburg.  Meanwhile the Germans, in pursuit of their policy of attaining economic independence,