A number of ingenious devices are employed in determining the quality of rubber goods as well as that of raw rubber. The principal tests to which manufactured rubber is subjected are those for abrasion and for stretching. In abrasion tests the sample is brought in contact with a rotating wheel of definite composition for a certain time and with a certain pressure, and the loss in weight of the rubber is afterwards determined. For stretching tests special machines are used in order to cut perfect rings from sheet of uniform thickness. The ring is tested by passing it round two rollers, which rotate at an even speed whilst they are gradually moved further and further apart by a stretching force, the amount of which is recorded upon a dial. The force required in order to produce a certain elongation, or to break the ring, may thus be determined.
We have now followed the fortunes of rubber from the wild territories of the Amazon to the plantation, and from the plantation to the factory. Here we may take leave of it, conscious that the last word on the subject is far from being said. In fact, we shall probably be safe in asserting that the future history of the rubber industry will be at least as interesting and eventful as its past history. At every stage of its career, rubber still presents problems which the planter and the manufacturer must join hands in solving, with the help of their scientific advisers.