Rubber and Rubber Products.—"Caoutchouc" is approximately the name given by Indians of the Amazon forests to a substance that had also been found in India. Some of it was brought to Europe from the Amazon region as early as 1736, and for nearly one hundred years no general purpose was discovered for which it could be used, except to erase lead-pencil marks—hence the name india-rubber, which has held ever since.
Common rubber is the prepared juice of a dozen or more shrubs and trees, all of which grow in tropical regions.[37] The belt of rubber-producing plants extends around the world and includes such well-known species as the fig, the manihot (or manioc), and the oleander; indeed, it is a condition of sap rather than a definite species of plant that produces rubber, and the latter is a manufactured rather than a natural product. The process of preparing the juice is practically the same in every part of the world.
The rubber-gatherer of the Amazon, who is practically a slave, wades into the swamp, makes several incisions in the bark of the tree, fashions a rough trough of clay under it, and waits till the sap fills the clay vessel. When the sap has been gathered he makes a fire of the nuts of the urucuri palm and places an inverted funnel over it to concentrate the smoke. He first dips the end of a wooden spindle into the juice and then holds it in the smoke until the juice coagulates; this process is repeated until there has formed a ball of rubber weighing from five to ten pounds. The smoke of the palm-nuts is a chemical agent that converts the juice into the crude rubber of commerce.
Crude gum, however, is lacking both in strength and elasticity. The process that makes it a finished product is known as vulcanization. The crude rubber, having been exported to the manufacturer in the United States or Europe, is shredded, washed, and cleansed, and partly fused with varying proportions of sulphur. For a very soft product, such as the inner surface of tires, only a small proportion is used; where the wear is considerable, a larger proportion is employed.[38] White clay is sometimes added to give body to the product; coloring matter is also sometimes added.
By far the greater part of the crude rubber comes from the Amazon forests. Brazil produces about one-half, but a considerable quantity is obtained in Acré, the territory formed where the borders of Brazil, Bolivia, and Peru meet, and now ceded to Brazil. Nearly all this product, that of the Ceará region excepted, is marketed at Pará and is known as Pará rubber. It is the best produced. The African product, mainly from the forests of the Kongo, and Madagascar, and nearly all the East Indian product is sent to Europe.
REGIONS YIELDING RUBBER
The world's product is about one hundred and thirty-three million pounds of crude rubber. Of this product the United States takes nearly one-half. The greater part is used in the manufacture of pneumatic tires, hose, and overshoes. A large part is used for making water-proof cloth,[39] and considerable is made into the small elastic bands for which there is a growing use.
Gutta-Percha.—Gutta-percha is obtained from the juices of several plants (chiefly Dichopsis gutta and Supota mülleri) both of which abound in the Malay peninsula and the East Indies. It is prepared in a manner somewhat similar to that employed in making crude rubber; it is also easily vulcanized by heating with sulphur. It is used to a limited extent in the manufacture of golf-balls, but mainly as the insulating cover of copper wires used in ocean telegraph cables. For this purpose it has no known substitute, and its essential merit is the fact that it is not altered by salt water. Nearly all the product is shipped from Singapore to England.