RUBBER 136 RUBBER the product is yielded from the stems of trees of Hevea, Manihot, Ficus, Castilloa and Funtumia, from the guayale plant Parthenium, and from the climbers, roots and leaves of other trees. These trees and plants grow in equatorial regions, some of them requiring a stony soil with an occasional rainfall and others a moist alluvial soil. Rubber is found in a solid state in the fiber of the Parthenium, and extraction from this shrub is easy. In the case of the other plants and trees the extraction of the product is more complicated. The calls of industry and commerce have used up enormous sup- plies of rubber in recent years, but heavy as the demand has been, the sources have shown no signs of exhaustion. In Ceylon and Malaya, Sumatra, Brazil, Bolivia, Peru, and in other areas of South Amer- ica, and the E., the cultivation of rubber has continually extended. Until recently the product harvested in the State of Para in Brazil was looked upon as the best in quality and the standard by which other grades of rubber were judged, but more recently the product from the East has improved both in quantity and quality. In 1900 very little plantation rubber could be found in the markets, yet in 1915 the amount exported from Ceylon and Malaya alone was nearly 100,000 tons. The United States is the largest importer and consumer of rubber among the nations. In 1904, 59,016,000 pounds were imported, and in 1915, 172,068,428 pounds. The use of rubber goes back almost to the period of the voyages of Columbus, for according to the accounts of that time, Columbus brought back to Spain rubber balls from Haiti; and in 1615 Juan de Torquemada talks of rubber trees, and of the use of the gum in the making of shoes and waterproofing of canvas. The name of India rubber seems to have come into vogue about the middle of the eigh- teenth century, when the product began to be attached to the end of pencils to rub out pencil marks. From that time onward rubber gradually came into use for one purpose or another all over the civilized world. Rubber in its crude state is obtained from the juice of the rubber tree, ranging from the Hevea brasiliensis, flourishing in the Amazon valley, to the tropical African variety which gives the rubber of commerce associated with that region. It is a fortunate fact that the milky juice of the tree which is the essence of rubber does not appear to be an element in its sap nor essential to its life, so that even unskillful harvesting is not fatal to the tree itself. The juice or latex is in its nature a secretion in which float small globules of rubber which when the juice is permitted to stand for a given time comes to the top like cream. A tree may in the course of the year yield up to 17 pounds. Before the scientific cultivation of rubber had been developed it was cus- tomary to cut the trees and saplings down and in that way procure the caout- chouc wholesale, but the method now in vogue, having in view the prolongation of the life of the tree, eliminates waste- fulness. The modern method is to make incisions in the trunk through which the rubber is drawn into clay cups held by the workers. The contents of the cups are later emptied into a large vessel, which is heated moderately so that the water may evaporate and the rubber harden into cakes ready for shipping. This is the method in vogue in the plan- tations where the best rubber of com- merce is drawn. In recent years botany and the allied sciences have lent their aid In the develop- ment of rubber cultivation. Waste has now been reduced to a minimum and even where the trees have been cut down methods of transplantation have been evolved. The method of collection is usu- ally through an incision made to resemble a herringbone, with a vertical channel toward which a series of oblique cuts have been made with the cup at the base to receive the fluid as it descends. The many uses to which natural rubber showed itself capable of being put natur- ally turned the thoughts of those who used it to the possibility of manufactur- ing rubber and experiments in that line were made from the beginning. One of the first uses to which rubber was put in manufacture was in waterproof cloth, and as flexible tubes and containers. Rub- ber boots were imported in 1852 into Boston from Brazil. A little before 1844 Charles Goodyear discovered the art of vulcanizing and this, with the discovery of Hayward that by mixing dry sulphur with rubber its stickiness was removed, added greatly to the commercial possibili- ties of the product. New methods of vulcanizing rubber were gradually per- fected, so that it became unchangeable under all ordinary conditions whether of heat, cold or moisture. When hardened by cold it does not become brittle. When subjected to heat or put in boiling water it does not dissolve but becomes more elastic. When kept stretched to many times its original length, it can be cut into elastic threads to be used in garters, gloves, etc. In a semi-liquid state it may be used as a cement, and combined with shellac and coal tar^ it forms a tenacious variety of glue. It is used as an element in varnish, and in many lubricating liquids. Apart from the making of tires, footwear, clothing, belting, surgical and
