analysis and some tedious tests to determine whether it contained methyl
or ethyl groups, whether it was an aldehyde or an ester, whether the
carbon atoms were singly or doubly linked and whether it was an open
chain or closed. But let him get a whiff of it and he can give instantly
a pretty shrewd guess as to these points. His nose knows.

Although the chemist does not yet know enough to tell for certain from
looking at the structural formula what sort of odor the compound would
have or whether it would have any, yet we can divide odoriferous
substances into classes according to their constitution. What are
commonly known as "fruity" odors belong mostly to what the chemist calls
the fatty or aliphatic series. For instance, we may have in a ripe fruit
an alcohol (say ethyl or common alcohol) and an acid (say acetic or
vinegar) and a combination of these, the ester or organic salt (in this
case ethyl acetate), which is more odorous than either of its
components. These esters of the fatty acids give the characteristic
savor to many of our favorite fruits, candies and beverages. The pear
flavor, amyl acetate, is made from acetic acid and amyl alcohol--though
amyl alcohol (fusel oil) has a detestable smell. Pineapple is ethyl
butyrate--but the acid part of it (butyric acid) is what gives Limburger
cheese its aroma. These essential oils are easily made in the
laboratory, but cannot be extracted from the fruit for separate use.

If the carbon chain contains one or more double linkages we get the
"flowery" perfumes. For instance, here is the symbol of geraniol, the
chief ingredient of otto of roses:

(CH_{3})_{2}C = CHCH_{2}CH_{2}C(CH_{3})_{2} = CHCH_{2}OH

The rose would smell as sweet under another name, but it may be