The New Student's Reference Work/Rubber Manufacture
Rub'ber Man'ufac'ture. In a number of different kinds of tropical trees is found a secretion that does not seem to be essential to the life of the tree, in which float minute globules of rubber. Many methods of securing this secretion, usually called rubber-milk, are employed; but the most common and economical way is to make incisions in the trunk of the tree. As the rubber-milk flows out, it is caught in a small cup of clay and at the end of each day emptied into a larger vessel, The old and still common way of separating the small globules of rubber from the rubber-milk is by evaporation. Where rubber-milk is collected in large quantities, however, a machine similar to a cream-separator is used. This collects the rubber on the top and drives the water and all impurities to the bottom. The manufacture of rubber began about 1820. The application of rubber to making waterproof cloth first gave commercial importance to rubber. The first to make this application of rubber was Charles McIntosh, who reduced it to a solution in naptha and spread it between two pieces of cloth. Waterproof coats still bear his name. Williams Chaffee developed a rubber-varnish for coating different materials to make them waterproof. The Roxbury Rubber Company was formed in 1833, and lor a time did a flourishing business, but it was soon found that the articles manufactured had a tendency to harden and crack in winter and become soft and sticky in summer. In the meantime Charles Goodyear was trying to overcome this defect by mixing pure rubber with various other substances. Nathaniel Hayward of Woburn, Mass., found that by mixing dry sulphur with pure rubber the stickiness was removed. Goodyear acquired Hayward's patent. By accident he dropped some of the mixture on a hot stove and found that it did not melt. He then placed it in extreme cold and found that its texture was not changed. Thus the art of vulcanizing rubber was discovered, for the process consists simply of mixing sulphur with pure rubber and then subjecting the mixture to moderate heat for a period of time. The mixture varies from soft to hard according to the amount of heat applied. Although sulphur is the only essential ingredient, others, as asphalt, carbonate of lead, magnesium, silicate or tar, are often added, each of which imparts a different quality to the product. Pure rubber is now used only to a limited extent in arts, but in its vulcanized state it is applied to an almost endless variety of purposes.