THE USES OF RUBBER.Rubber is used in flooring, auto mobile tires, belts, and machine foundations. In electrical science, it is used as an insulating material; while its value as a waterproofing agent is of fundamental importance. It also enters into hose, surgical goods, sporting goods, cements and other groups of articles and compounds. For many purposes satis factory substitutes for rubber do not exist.
Synthetic rubber is the result of a purely chemical process. In composition and in properties it is equivalent to, or the same as, natural rubber. Thus far synthetic rubber is a scientific truth rather than a practical success. The fact that artificial rubber can be prepared in laboratories, and that such rubber is practi cally identical with that obtained from trees, is beyond question; but the cost of such rubber is yet so high that very little of it is manufactured.
The ultimate value of synthetic rubber must obviously depend upon its cost and quality. Assuming the quality to be satisfac tory, methods will have to be devised whereby parent substances can be prepared in larger quantities and more cheaply than at present. The problem is complicated by the fact that, with present knowledge, it seems necessary that parent substances should be particularly pure.
It has long been known that an intimate relationship exists between indiarubber and a group of substances, of which isoprene and butadiene are at present the most notable. In 1860, Williams isolated what is now known as isoprene, from products obtained from the destructive distillation of rubber. In 1875, Bouchardat suggested that under cer tain conditions isoprene might be converted back again into rubber. In 1892, Tilden discovered that some old specimens of isoprene obtained from turpentine had converted themselves into rubber without assist ance; and, in 1909, Hofmann and others suggested the methods that are now employed.
Isoprene is obtained in several ways, as from fusil oil, and by condens ing vapors of turpentine over iron at temperatures of from 55° degrees C. to 600 degrees C. (English patent 27908 of 1909). Butadiene is also obtained in several ways, as from products obtained by fermenting the dried pulp of potatoes (Detoeuf, Nature, 1912, p. 306). Of the two parent substances mentioned, isoprene is a colorless liquid-hydrocarbon in which the hydrogen and carbon exist in the same proportions as in ordinary rubber. The transformation of isoprene to rubber is obtained by placing isoprene, selected for its purity, under pressure, and then heating it, with or without the intervention of other substances. Or else, it is transformed by the influence of small quantities of other sub stances, as metallic sodium.