Avogadro constant Avogadro constant In chemistry and physics, the Avogadro constant, named after scientist Amedeo Avogadro, is the number of constituent particles, usually atoms or molecules, that are contained in the amount of substance given by one mole. Thus, it is the proportionality factor that relates the molar mass of a substance to the mass of a sample. The Avogadro constant, often designated with the symbol "N" or "L", has the value in the International System of Units (SI). (The parentheses there represent the degree of uncertainty.) Previous definitions of chemical quantity involved the Avogadro number, a historical term closely related to
Grain (unit) cod. gr. ss tablets" (using the medical abbreviations ASA for aspirin, c̄ for "with", and cod. for codeine). The apothecaries' system has gradually been replaced by the metric system, and the use of the grain in prescriptions is now rare. Particulate emission levels, used to monitor and regulate pollution, are commonly measured in grains per cubic foot. This is the same unit commonly used to measure the amount of moisture in the air, also known as the absolute humidity. The SI unit used to measure particulate emissions and absolute humidity is mg/m. One grain per cubic foot is approximately .