A metal of a bright silver-white color, derived in 1807 by Sir Humphrey Davy from potash. It is prepared by heating together potash and carbon to a high temperature in an iron retort. It is lighter than water, brittle at 320 Fahrenheit, malleable at a little higher temperature, melts at 620, and when heated to a temperature below red heat it yields a fine green-colored vapor. It has a strong affinity for oxygen, taking fire when thrown upon water or ice, and oxidizes so readily that to be preserved it must be kept in substances which contain no oxygen, as naphtha or kerosene. Its com pounds are very important, being used in-glass and soap making, in artificial manures, and in many drugs and chemicals. The most important of the salts of potassium are potash, nitre or saltpetre, chlorate of potash, and cream of tartar.