lving the
nitrate question. We gave the Government $20,000,000 to experiment on
the production of nitrates from the air and the results will serve for
fields as well as firearms. But the question of an independent supply of
cheap potash is still unsolved.

IV

COAL-TAR COLORS

If you put a bit of soft coal into a test tube (or, if you haven't a
test tube, into a clay tobacco pipe and lute it over with clay) and heat
it you will find a gas coming out of the end of the tube that will burn
with a yellow smoky flame. After all the gas comes off you will find in
the bottom of the test tube a chunk of dry, porous coke. These, then,
are the two main products of the destructive distillation of coal. But
if you are an unusually observant person, that is, if you are a born
chemist with an eye to by-products, you will notice along in the middle
of the tube where it is neither too hot nor too cold some dirty drops of
water and some black sticky stuff. If you are just an ordinary person,
you won't pay any attention to this because there is only a little of it
and because what you are after is the coke and gas. You regard the
nasty, smelly mess that comes in between as merely a nuisance because it
clogs up and spoils your nice, clean tube.

Now that is the way the gas-makers and coke-makers--being for the most
part ordinary persons and not born chemists--used to regard the water
and tar that got into their pipes. They washed it out so as to have the
gas clean and then ran it into the creek. But the neighbors--especially
those who fished in the stream below the gas-works--made a fuss about
spoiling the water, so the gas-men gave away the tar to the boys for use
in celebrating the Fourth of July and election night or sold it for
roofing.

[Illustration: THE PRODUCTION OF COAL TAR

A battery of Koppers by-product coke-ovens at the plant of the Bethlehem
Steel Company, Sparrows Point, Maryland. The coke is being pushed out of
one of the ovens into the waiting car. The vapors given off from the
coal contain ammonia and the benzene compound used to make dyes and
explosives]

[Illustration: IN THESE MIXING VATS AT THE BUFFALO WORKS, ANILINE DYES
ARE PREPARED]

But this same tar, which for a hundred years was thrown away and nearly
half of which is thrown away yet in the United States, turns out to be
one of the most useful things in the world. It is one of the strategic
points in war and commerce. It wounds and heals. It