Constant

CONSTANT, a value that characterizes certain physical properties of a given substance and is constant for it under given conditions. For example, by C. one can understand the value of the specific resistance of copper, which represents the resistance of a copper rod having 1 cm² cross-sectional area and 1 cm length. The thermal conductivity of a substance, its specific heat, its hardness, its coefficient of elasticity, etc., are C.s characterizing the given substance. In order to be able to conveniently use physical C.s, there are a number of collections of C.s. The most well-known of these is the collection formerly published by Landolt in Germany and now issued in many editions. The French Physical-Chemical Society, under the direction and editorship of Marie, publishes an excellent collection of 'Physical Constants'. Similar publications exist in England and America. In our country, a similar reference work is published by the 'Technical Encyclopedia'.-The physical and chemical constants of a given substance, which allow determining its identity (identity) and chemical purity, are widely used for practical purposes in establishing standard requirements for all kinds of products. The collection of standards for pharmaceutical preparations is the pharmacopoeia, which gives C.s and indicates the methods and conditions for their determination. C.s of the pharmacopoeia: specific gravity, solubility, sublimation, melting point, solidification point, boiling point, rotation of the plane of polarization, value of refraction, viscosity, and many others. Since a huge number of medications are not chemically individual substances, these C.s are of decisive importance in determining the quality of medications. Chemical C.s in testing medications are: acetyl number, ester number, acid number, saponification number, Reichert-Meissl number, Polenske number, bromine number, iodine number, concentration of hydrogen ions, and many others.