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 (Washings) ammonium sulfate (7-25 pounds)
      Tar (120 pounds) benzene (10-20 pounds)
                        toluene (3 pounds)
                        xylene (1-1/2 pounds)
                        phenol (1/2 pound)
                        naphthalene (3/8 pound)
                        anthracene (1/4 pound)
                        pitch (80 pounds)
      Coke (1200-1500 pounds)

When the tar is redistilled we get, among other things, the ten “crudes” which are fundamental material for making dyes.  Their names are:  benzene, toluene, xylene, phenol, cresol, naphthalene, anthracene, methyl anthracene, phenanthrene and carbazol.

There!  I had to introduce you to the whole receiving line, but now that that ceremony is over we are at liberty to do as we do at a reception, meet our old friends, get acquainted with one or two more and turn our backs on the rest.  Two of them, I am sure, you’ve met before, phenol, which is common carbolic acid, and naphthalene, which we use for mothballs.  But notice one thing in passing, that not one of them is a dye.  They are all colorless liquids or white solids.  Also they all have an indescribable odor—­all odors that you don’t know are indescribable—­which gives them and their progeny, even when odorless, the name of “aromatic compounds.”

[Illustration:  Fig. 8.  Diagram of the products obtained from coal and some of their uses.]

The most important of the ten because he is the father of the family is benzene, otherwise called benzol, but must not be confused with “benzine” spelled with an i which we used to burn and clean our clothes with.  “Benzine” is a kind of gasoline, but benzene alias benzol has quite another constitution, although it looks and burns the same.  Now the search for the constitution of benzene is one of the most exciting chapters in chemistry; also one of the most intricate chapters, but, in spite of that, I believe I can make the main point of it clear even to those who have never studied