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weight (wat)

The product of the force of gravity, defined internationally as 9.80665 m/s2, times the mass of the body. [A.S. gewiht]
apothecaries' w. an obsolescent system of w.'s based upon the w. of a grain of wheat. Has been used for centuries in weighing medicines and precious metals (Troy measure). Some drugs which have been available for long periods are still often designated as grains (e.g., 5 grains of aspirin, 1/2 grain of codeine, 1/100 grain nitroglycerin). This w. system has been largely superseded by the metric system (based on grams). One grain is the equivalent of 64.8 milligrams. One scruple contains 20 grains; one dram contains 60 grains; one apothecary ounce contains 8 drams (480 grains); one apothecary pound contains 12 ounces (5760 grains).
atomic w. (at wt, AW) the mass in grams of 1 mol (6.02 x 1023, atoms) of an atomic species; the mass of an atom of a chemical element in relation to the mass of an atom of carbon-12 (12C), which is set equal to 12.000, thus a ratio and therefore dimensionless (although the actual mass, numerically the same, is sometimes expressed in daltons); not necessarily the w. of any individual atom of an element, since most elements are made up of several isotopes of different masses; e.g., the atomic w. of chlorine is 35.4527, because it is composed of 35Cl and 37Cl in proportions that give an average of 35.4527. See also molecular w.
birth w. in humans, the first w. of an infant obtained within less than the first 60 completed minutes after birth; a full-size infant is one weighing 2500 g or more; a low birth w. is less than 2500 g.
combining w. gram equivalent
dry w. the w. of material remaining after removing the water (e.g., after heating above 100°C).
equivalent w. gram equivalent
gram-atomic w. atomic w. expressed in grams. Cf. mole.
gram-molecular w. molecular w. expressed in grams. Cf. mole.
molecular w. (mol wt, MW) the sum of the atomic w.'s of all the atoms constituting a molecule; the mass of a molecule relative to the mass of a standard atom, now 12C (taken as 12.000). Relative molecular mass (Mr) is the mass relative to the dalton and has no units. See also atomic w.molecular mass, molecular weight ratio, relative molecular mass;


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