shings) 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 chemistry--provided they retain
their childish liking for puzzles. It is really much like putting
together the old six-block Chinese puzzle. The chemist can work better
if he has a picture of what he is working with. Now his unit is the
molecule, which is too small even to analyze with the microscope, no
matter how high powered. So he makes up a sort of diagram of the
molecule, and since he knows the number of atoms and that they are
somehow attached to one another, he re