CAFFEINE, the stimulant principle in coffee, was discovered by Runge in 1820. He obtained it by precipitating a cold infusion of coffee by acetate of lead, and throwing down the lead by sulphuretted hydrogen. It was obtained in colourless acicular crystals. It contains 21.6 per cent. of nitrogen, a larger quantity of that gas than is yielded by any other organic compound except urea and uric acid. Caffeine is identical in composition with theine. See CHEMISTRY.