Potassium

a bright, silvery metal lighter than water. At ordinary temperature it may be cut with a knife, but at the freezing temperature of water it becomes brittle. Its affinity for moisture is so strong that if a bit be laid on water it decomposes the water; part of the potassium unites with the oxygen, part unites with the hydrogen, burning with a characteristic blue flame. Potassium cannot be kept in the open air, but is protected usually in bottles and is covered with oil. Potassium forms many compounds. One of the best known is potash, a solution of which, obtained usually from wood ashes, is called lye. Another well known compound is saltpeter, the potassium nitrate used in making gunpowder. Potassium has too great an affinity for other elements to be found free in nature. It is widely distributed. It forms a part of many rocks and, by their disintegration, enters into the composition of most soils. It is stored up by plants and becomes a part of the bodies of animals. The eke or oil exuded by the body of the sheep and found on wool is strong with potassium. Metallic potassium is prepared by a process of distillation. Pearlash is heated with charcoal in a red-hot iron retort--a process not without danger. The pearlash, or carbonate of potassium, was obtained formerly from wood ashes, but the greasy products of wool and a residuum obtained in the manufacture of beet sugar now yield the greater part of the pearlash from which the potassium of the arts is prepared. In a compound form potassium enters into the makeup of saltpeter, gunpowder, potash, soap, alum, cream of tartar, and "caustic."