the volatile colorless liquid he had put into it.

Twenty years before the discovery would have been useless, for sodium
was then a rare and costly metal, a little of it in a sealed glass tube
being passed around the chemistry class once a year as a curiosity, or a
tiny bit cut off and dropped in water to see what a fuss it made. But
nowadays metallic sodium is cheaply produced by the aid of electricity.
The difficulty lay rather in the cost of the raw material, isoprene. In
industrial chemistry it is not sufficient that a thing can be made; it
must be made to pay. Isoprene could be obtained from turpentine, but
this was too expensive and limited in supply. It would merely mean the
destruction of pine forests instead of rubber forests. Starch was
finally decided upon as the best material, since this can be obtained
for about a cent a pound from potatoes, corn and many other sources.
Here, however, the chemist came to the end of his rope and had to call
the bacteriologist to his aid. The splitting of the starch molecule is
too big a job for man; only the lower organisms, the yeast plant, for
example, know enough to do that. Owing perhaps to the _entente cordiale_
a French biologist was called into the combination, Professor Fernbach,
of the Pasteur Institute, and after eighteen months' hard work he
discovered a process of fermentation by which a large amount of fusel
oil can be obtained from any starchy stuff. Hitherto the aim in
fermentation and distillation had been to obtain as small a proportion
of fusel as possible, for fusel oil is a mixture of the heavier
alcohols, all of them more poisonous and malodorous than common alcohol.
But here, as has often happened in the history of industrial chemistry,
the by-product turned out to be more valuable than the product. From
fusel oil by the use of chlorine isoprene can be prepared, so the chain
was complete.