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 supplies munitions and medicines.  It is like the magic purse of Fortunatus from which anything wished for could be drawn.  The chemist puts his hand into the black mass and draws out all the colors of the rainbow.  This evil-smelling substance beats the rose in the production of perfume and surpasses the honey-comb in sweetness.

Bishop Berkeley, after having proved that all matter was in your mind, wrote a book to prove that wood tar would cure all diseases.  Nobody reads it now.  The name is enough to frighten them off:  “Siris:  A Chain of Philosophical Reflections and Inquiries Concerning the Virtues of Tar Water.”  He had a sort of mystical idea that tar contained the quintessence of the forest, the purified spirit of the trees, which could somehow revive the spirit of man.  People said he was crazy on the subject, and doubtless he was, but the interesting thing about it is that not even his active and ingenious imagination could begin to suggest all of the strange things that can be got out of tar, whether wood or coal.