y compound that he can analyze. He
cannot only imitate the manufacturing processes of the plants and
animals, but he can often beat them at their own game.

When coal is heated in the open air it is burned up and nothing but the
ashes is left. But heat the coal in an enclosed vessel, say a big
fireclay retort, and it cannot burn up because the oxygen of the air
cannot get to it. So it breaks up. All parts of it that can be volatized
at a high heat pass off through the outlet pipe and nothing is left in
the retort but coke, that is carbon with the ash it contains. When the
escaping vapors reach a cool part of the outlet pipe the oily and tarry
matter condenses out. Then the gas is passed up through a tower down
which water spray is falling and thus is washed free from ammonia and
everything else that is soluble in water.

This process is called "destructive distillation." What products come
off depends not only upon the composition of the particular variety of
coal used, but upon the heat, pressure and rapidity of distillation. The
way you run it depends upon what you are most anxious to have. If you
want illuminating gas you will leave in it the benzene. If you are after
the greatest yield of tar products, you impoverish the gas by taking out
the benzene and get a blue instead of a bright yellow flame. If all you
are after is cheap coke, you do not bother about the by-products, but
let them escape and burn as they please. The tourist passing across the
coal region at night could see through his car window the flames of
hundreds of old-fashioned bee-hive coke-ovens and if he were of
economical mind he might reflect that this display of fireworks was
costing the country $75,000,000 a year besides consuming the
irreplaceable fuel supply of the future. But since the gas was not
needed outside of the cities and since the coal tar, if it could be sold
at all, brought only a cent or two a gallon, how could the coke-makers
be expected to throw out their old bee-hive ovens and put in the
expensive retorts and towers necessary to the recovery of the
by-products? But within the last ten years the by-product ovens have
come into use and now nearly half our coke is made in them.

Although the products of destructive distillation vary within wide
limits, yet the following table may serve to give an approximate idea of
what may be got from a ton of soft coal:

1 ton of coal may give
Gas, 12,000 cubic feet
Liquor (Wa