The gumshoes or galoshes
that he was then enabled to make still go by the name of "rubbers" in
this country, although we do not use them for pencil erasers.
Goodyear found that he could vary this "vulcanized rubber" at will. By
adding a little more sulfur he got a hard substance which, however,
could be softened by heat so as to be molded into any form wanted. Out
of this "hard rubber" "vulcanite" or "ebonite" were made combs,
hairpins, penholders and the like, and it has not yet been superseded
for some purposes by any of its recent rivals, the synthetic resins.
The new form of rubber made by the Germans, methyl rubber, is said to be
a superior substitute for the hard variety but not satisfactory for the
soft. The electrical resistance of the synthetic product is 20 per cent,
higher than the natural, so it is excellent for insulation, but it is
inferior in elasticity. In the latter part of the war the methyl rubber
was manufactured at the rate of 165 tons a month.
The first pneumatic tires, known then as "patent aerial wheels," were
invented by Robert William Thomson of London in 1846.
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