The New Student's Reference Work/India-Rubber

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India-Rub′ber or Gum Elas′tic is a substance found in the milky juice of certain plants in tropical and subtropical countries.  The principal tree from which it is obtained is tall and graceful.  Its appearance is well-known, and the glossy leaves have been seen on small trees grown in pots as ornamental plants.  Some of the properties of india-rubber must have been known in America at a very early period, for it is related by travelers as early as Columbus’ second voyage that the Haitians made balls of the “gum of a tree,” which bounced better than the wind-balls of Spain.  India-rubber was first imported for rubbing out from paper marks made with black lead (1770), whence its name.  In 1820 it began to be used in the many useful ways in which we find it to-day.  It is gathered by making cuts in the trunks of the trees.  In a few hours the juice fills the clay basins placed to receive it.  A good tree will yield four ounces of juice daily and twenty gallons in a season.  A gallon will produce two pounds of good rubber.  It is made solid by drying in the sun or in other ways.  To purify the raw material, it is boiled and pressed through powerful machines, rolled out into thin plates and then dried the second time.  One pound of rubber will make 32,000 yards of thread.  Pure rubber is very little used now, but in its vulcanized state the uses to which it is put are innumerable.  The process of vulcanizing rubber, which has made it available for many purposes, was discovered by Goodyear (q. v.), and consists in heating the pure rubber with sulphur, which hardens it.  It is used in making shoes, cloth, belting, tires, hose, washers, tobacco-pouches, combs, chains, bracelets, paper-knives, furniture, rails and paving.  There have been many efforts to obtain a substitute for India-rubber, as the raw material is expensive, but so far without success.