, can be made in just the same way as isoprene from isoamyl alcohol. Butadiene is the next lower homologue of isoprene, and when it is treated with sodium it produces a substance very like rubber which is called nor-caoutchouc. It is said that its quality is even superior to that of ordinary rubber. As there are a number of alcohols homologous to butyl and isoamyl alcohol, a number of substances similar to isoprene and butadiene can be made from them, and from these by the action of sodium a series of rubbers. It is said that the rubber produced by the action of acetic acid on isoprene is identical with natural rubber, and that the rubber made by the action of sodium is slightly different in its chemical reactions. It may be that all natural rubbers are not identical and that the difference between Para rubber and plantation rubber may depend upon some slight differences in the caoutchouc itself and that what the chemist does with extreme difficulty when he changes starch into rubber, nature does with ease, and, as the chemist may get slightly different products by pursuing different methods, so nature may get different products under different circumstances. It was said at the beginning of this paper that rubber has the empirical formula . It seems that the formula is more correctly written and that the name 1.5 dimethyl cyclooctadiene 1.5 represents the structure of Para rubber, while the rubber produced by the action of sodium on isoprene is
1.5 dimethyl cyclooctadiene 1.3
or 1.5 dimethyl cyclooctadiene 1.7
Dr. Duisberg, of Elberfeld, stated in his address to the Congress of Applied Chemistry at New York in 1912 that he had for some time used tires of artificial rubber on an automobile. The German Emperor has also received a present of similar tires. The rubber can be made, but it is still far too expensive to compete with natural rubber.
Closely connected with the history of the rubber industry are the Congo atrocities. Congo rubber is not so good for most purposes and commands a lower price, though, being softer, it is said to be better as a filling for driving belts and for other uses. It is obtained from Landolphia vines, which are not usually tapped, but cut off, the latex being extracted all at once. This fact may be partly responsible for the atrocities, since, the more accessible sources of supply having been depleted, the natives have been obliged to go farther and farther in order to obtain the rubber demanded of them.
In the sixties and seventies of the last century, central Africa became known to Europe, and the commercial interests of the various nations led to what is termed the "Scramble for Africa." Stanley's discovery of the Upper Congo induced King Leopold to form the "International African Association" and he sent several investigating expeditions at
