The process of hardening rubber by adding sulphur and heating the mixture is vulcanisation. Vulcanisation was discovered by Charles Goodyear. Raw rubber is sticky. It hardens when the temperature is low and softens when it is high. Charles Goodyear discovered that by combining raw rubber with sulphur and by heating it, the rubber becomes stronger and elastic and also resistant to solvents. Today almost all rubber, whether natural or synthetic is vulcanized.   _{Your Comment}