Page:The New International Encyclopædia 1st ed. v. 17.djvu/362

* KUBBER. 330 ETJBBER. Tlic liist record of imlia-ruljljci- was made in aceouiits of Columbus's second voyage to America, where it is related that he fouml the inhabitants of Uispaniola (Haiti) amusing themselves with rubber balls. In a book publislied in iladrid in 1015, Juan- de Toniuemada mentions the tree whieli yields rubber in Mexico, describes the mode of collecting the gum, and states that it is made into shoes; also that the Spaniards use it for waxing their canvas cloaks to make them resist water. It was at first known by the name of ilastic giiiii. and received that of india-rubber from the discovery of its use for rubbing out lead-pencil marks. It is stated that the first rubber «as brought into the United States in 1800, the very year in which was born Charles Goodyear (q.v. ), a man whose inventions made possible the modern rubber industry. India-rubber is obtained from the milky juice of the rubber tree. This is not the true sap, but a secretion which does not seem to be essential to the life of the plant. In this juice float minute globules of rubber which, when the juice is al- lowed to stand, rise to the top, like cream. Vari- ous methods are employed for collecting the sap, the future character of the rubber depending much upon how this is done and the separation of the caoutchouc from the aqueous liquid is ef- fected. The annual yield of a single tree is from 2 or 3 to 16 or 17 pounds. The rubber is some- times collected by simply cutting the trees down, but this wasteful method has been in most eases abandoned, and it is customary to make incisions in the trunk through which the milk oozes out. The trees are tapped at sunrise, as the milk is supposed to flow more freelj' during the morning hours. The first row of incisions is often made in a circle surrounding the tree about six feet from the ground, the next morning a row somewhat lower down is made, and so on, each succeeding morning till the ground is reached. In each in- cision a little clay cup, molded by the workman and holding about a gill, is placed, and its eon- tents emptied daily into a larger vessel, in which it is allowed to smolder over a slow fire until the water is evaporated and the rubber shaped into cakes is ready for export. This is the almost universal method of collecting Para rubber. Re- cently, however, in regions where the rubber milk is collected in large amounts, a more scientific means has been adopted for obtaining the caout- chouc by using a machine similar to a cream separator which collects the rubber on the top quite as efi'ectuall_v, and causes the water and all impurities to be driven to the bottom. A favorite but wasteful way of collecting rub- ber is followed by the natives of Central America and Assam, who allow the milk to run into a hole in the ground and after the water is ab- .sorbed a spongy mass is left, mixed with dust and leaves. In Africa and New Guinea the natives smear their bodies with the milk, and after this has evaporated scrape off the layer of caoutchouc which has dried on the skin and mold it into little slabs or cubes. In Fiji the milk is taken into the mouth and the small pellets thus formed arc heaped and molded into balls. In Borneo. Africa, and some parts of Brazil, salt water is used to form the clot. The Pernanihuco rubber of commerce is produced in this way. Sometimes the milk is simply allowed to trickle down the tree and dry in tears as it flows. These scraps and strings are collected and molded into balls. The Vi:uru rulibcr, a dry elastic rubber, free from stickiness, is i)rc)duced in this way. At the clo.se of the nineteenth century the world's aiuuuil production of rubber was about 57,500 tons, of which 21,000 tons are consumed in the United States and Canada and as much more in Great Britain, Of this amount the chief producers were: the Amazon district, 25,000 tons; the rest of South America, 3,500 tons : Java and Borneo, 1000 tons; East and West Africa, 24,000 tons; India, Burma, and Ceylon, 500 tons. The manufacture of rubber did not begin till about 1S20. The application of rubber to the making of waterproof cloth first gave it commer- cial importance, although it had been previously made into flexible tubes, for the use of surgeons and chemists, and into bottles. Waterproof clofh was first made by Charles ISIcIntosh, a Scotch chemist, who reduced the rubljcr to a solution in naphtha and spread it between two layers of cloth. Waterproof coats still bear his name. In 1852 a Boston sea-captain imported into America 500 iiairs of rubber boots which had been made by the natives of Brazil. These were readily sold for from $3 to .$5 per pair, and a great demand for them was created. During the next 15 years probably more than 1,000,000 pairs were sold. In the meantime William Chaffee had developed a rubber varnish for coating difl'erent materials to make them waterproof. In 1833 the Eoxbury India Rubber Company was formed and for a time the new enterprise flourished. But it was soon found that these waterproofed articles had an unfortunate tendency to grow hard and crack in the winter and to become soft and sticky in the summer. The demand for them ceased and their manvifacture was given up, Charles Goodyear, an unsuccessful merchant, in the meantime had turned his attention to the manufacture of rubber goods and was striving to find some process which would obviate the defects of pure rubber and render it less susceptible to the influence of heat and cold. He tried mixing it with magnesium, with quicklime and water, and with nitric acid. It had already been discovered by Leu- dersdorf, a German chemist, and also by Xathaniel Ha.^^vard of Woburn, JIass,, that by mixing dry sulphur with rubber its stickiness was removed, Hayward's patent and process were acquired by Goodyear, who, by accident, dropped upon a hot stove some of the mixture, and found to his as- tonishment that the high heat did not melt it. He next placed it in extreme cold and its texture still remained unchanged. Thus after years of patient experimenting, the art of vulcniiizing was accidentally discovered. Goodyear immediately developed the process and placed it upon a com- mercial basis. Vulcanizing is simply the process of mixing sulphur with rubber and then subjecting the mi.x- ture to moderate heat (say 300° F. ) for six or more hours. Its effect is to render rubber elas- tic, impervious, and unchangeable in texture under all ordinary conditions. The product varies from soft to hard, according to the amount of sulphur and heat applied. Although sulphur is the only essential ingredient, other materials are often added at the same time, as silicate of magnesium, carbonate of lead, asphalt, and tar, each of which imparts a different quality to the product. Commercial rubber is a tough fibrous sub- stance, possessing elastic properties in the highest