Potassium oxide hydroxide. It is deliquescent and will absorb water from the atmosphere, initiating this vigorous reaction. The chemical formula KO (or simply 'K') is used in several industrial contexts: the N-P-K numbers for fertilizers, in cement formulas, and in glassmaking formulas. Potassium oxide is often not used directly in these products, but the amount of potassium is reported in terms of the KO equivalent for whatever type of potash was used, such as potassium carbonate. For example, potassium oxide is about 83% potassium by weight, while potassium chloride is only 52%. Potassium chloride provides less potassium than an equal amount of
Chemical element plants, the calcium in mollusc shells, or the iron in the hemoglobin in vertebrate animals' red blood cells. The concept of an "element" as an undivisible substance has developed through three major historical phases: Classical definitions (such as those of the ancient Greeks), chemical definitions, and atomic definitions. Ancient philosophy posited a set of classical elements to explain observed patterns in nature. These "elements" originally referred to "earth", "water", "air" and "fire" rather than the chemical elements of modern science. The term 'elements' ("stoicheia") was first used by the Greek philosopher Plato in about 360 BCE in his dialogue Timaeus,