directly from turpentine so we may be independent of Formosa
and Borneo.

When we have a six carbon ring without double linkings (cyclo-aliphatic)
or with one or two such, we get soft and delicate perfumes like the
violet (ionone and irone). But when these pass into the benzene ring
with its three double linkages the odor becomes more powerful and so
characteristic that the name "aromatic compound" has been extended to
the entire class of benzene derivatives, although many of them are
odorless. The essential oils of jasmine, orange blossoms, musk,
heliotrope, tuberose, ylang ylang, etc., consist mostly of this class
and can be made from the common source of aromatic compounds, coal tar.

The synthetic flavors and perfumes are made in the same way as the dyes
by starting with some coal-tar product or other crude material and
building up the molecule to the desired complexity. For instance, let us
start with phenol, the ill-smelling and poisonous carbolic acid of
disagreeable associations and evil fame. Treat this to soda-water and it
is transformed into salicylic acid, a white odorless powder, used as a
preservative and as a rheumatism remedy. Add to this methyl alcohol
which is obtained by the destructive distillation of wood and is much
more poisonous than ordinary ethyl alcohol. The alcohol and the acid
heated together will unite with the aid of a little sulfuric acid and we
get what the chemist calls methyl salicylate and other people call oil
of wintergreen, the same as is found in wintergreen berries and birch
bark. We have inherited a taste for this from our pioneer ancestors and
we use it extensively to flavor our soft drinks, gum, tooth paste and
candy, but the Europeans have not yet found out how nice it is.

But, starting with phenol again, let us heat it with caustic alkali and
chloroform. This gives us two new compounds of the same composition, but
differing a little in the order of the atoms. If you refer back to the
diagram of the benzene ring which I gave in the last chapter, you will
see that there are six hydrogen atoms attached to it. Now any or all
these hydrogen atoms may be replaced by other elements or groups and
what the product is depends not only on what the new elements are, but
where they are put. It is like spelling words. The three letters _t_,
_r_ and _a_ mean very different things according to whether they are put
together as _art_, _tar_ or _rat_. Or, to take a more apposite
illustrati