The method of vulcanisation, which ranks among the most important of all industrial discoveries, was first found out in America by Goodyear. In England, Hancock shortly afterwards arrived at the same method independently. The following facts will help the reader to realise the far-reaching importance of vulcanisation.
Raw rubber becomes soft and sticky when heated, and when cooled beyond a certain point it becomes stiff and almost horny in consistency. Vulcanised rubber retains its physical properties almost unaltered over a range of temperatures extending from the freezing point to the boiling point of water. After prolonged immersion in water, raw rubber absorbs as much as 25 per cent, of its own weight of moisture. On the other hand, "The water absorption of vulcanised rubber is extremely small certainly not large enough to appreciably affect the insulation of a rubber cable after five years' continuous immersion" (Weber). From these facts the enormous increase in the durability and general usefulness of vulcanised rubber at once becomes apparent. Moreover, according to the proportion of sulphur which has entered into combination with the rubber, the physical properties of the finished product can be made to vary from those of the softest elastic up to those of the hardest vulcanite.