Accelerator (of vulcanization) – Any substance, which hastens the vulcanization of rubber causing it to take place in shorter time or at a lower temperature. In earlier days basic oxides such as limes, litharge and magnesia were recognized as having this function. Nowadays the important accelerators are organic substances containing either nitrogen or sulfur or both. According to potency, or speed of action, accelerators are sometimes classified as slow, medium, rapid, semi-ultra and ultra-accelerators. Most accelerators enhance tensile properties, and many improve age resistance.