Rubber From America

Left, Latex being collected from a tapped rubber tree, Cameroon.
Center, A woman in Sri Lanka harvesting rubber, c. 1920.
Right, Compression molded (cured) rubber boots before the flashes are removed.

        To the natives of tropical America must be given the credit for the first utilization of the latex from which rubber is made. Latex is a milky juice exuding from certain plants. It is said that when Columbus made his second visit to the New World he found the natives playing with balls made of crude rubber. The Europeans were amazed at the elasticity of the substance and the manner in which the balls bounced when dropped. So really the first use of rubber, as far as we know, was for balls.
       John Priestly, the English chemist, used the strange substance for rubbing out pencil marks, and thereafter it was known as rubber. Practically worthless a hundred years ago, rubber now ranks as a commodity of prime importance. Although rubber-producing trees have been cultivated only during the past fifty years the use of rubber in modern industry has increased constantly, until today it is regarded as one of the principal forest products of tropical regions.
       A large portion of rubber is used for tires and inner tubes in the United States and it could not have reached its present usefulness had it not been for the work of Charles Goodyear, who in 1839 successfully vulcanized it. Vulcanization is a process in which other materials, usually including sulphur, are combined with the rubber; the final product is harder and more durable. Vulcanized rubber can be used for many more purposes than untreated rubber.
       Almost all of the world’s rubber is obtained from a Brazilian tree, the Para rubber tree, a native of the dense forests flanking the Amazon River. To the botanist this tree is known as Hevea brasiliensis, a member of the Spurge family. Only a small quantity of rubber is now gathered from trees growing wild on the Amazon. The bulk of the world’s supply is produced on plantations in the East Indies and Malay Peninsula where the Hevea tree has been introduced and flourishes as well as in its native habitat. In the early 1940s is was also planted on the Tapajoz River, in the lower Brazilian Amazon.
       Many plants yield latex that dries as an elastic substance, but the product of most of them is of little or no use. Rubber from various sources differs greatly in its properties so that it cannot all be utilized for the same purposes. Latex, a plant sap, flows through minute tubes or elongated vessels which lie in the soft inner bark close to the vital wood layers. Unless great caution is taken when cutting the bark the tree may easily be permanently injured. Incisions made in the bark open these tiny vessels and the latex oozes out and drips into a cup which has been fastened at the base of the tree.
       Smoke from fire built of palm nuts produces a good cure for the rubber. A paddle is dipped in the liquid rubber and a layer of latex is picked up which is hardened by exposing it to the smoke of the fire. The heat drives off the water and layers of rubber accumulate on the paddle to form a large ball. Crude rubber balls ready for export may weigh from twenty to one hundred pounds. Plantation rubber is coagulated with chemicals.
       There are other rubber-producing plants of some note in the new world, besides the Pard rubber tree. The Andean rubber tree, Sapium, yields an inferior product. Castilla or Mexican rubber, commonly found in Central America, was once cultivated on a fairly considerable scale. Its latex is greatly inferior to the Pard rubber. Consequently the plantations established in the past have been abandoned.
       Ceard rubber, a close relative of the cassava plant from which tapioca is produced, is furnished by a plant growing in the arid regions of northeastern Brazil.
       A North American rubber plant which is not a tree but a small shrub is of interest as a good source of rubber for lead pencil erasers. “Guayule” grows wild in the arid regions of northern Mexico and southwestern United States. The rubber is scattered throughout the entire shrub and, to remove the rubber, the plant is macerated and washed in water.
       Balata of northern South America is the source of a non-elastic substance used for machine belting. Another latex commonly known as chicle is the base of chewing gum, while the latex of the so-called “cow-tree” of Venezuela is much esteemed by the Indians for caulking canoes. Marie B. Pabst

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