Molecular weight is the sum of the atomic weights of all the atoms in molecule. It is an integral multiple of the empirical formula weight found by chemical analysis, and of the equivalent weight. Molecular weights may be found directly by mass spectrometry, or deduced from related physical properties including gas density; effusion; osmotic pressure (see osmosis, and effects on solvents: lowering of vapor pressure and freezing point, and raising of boiling point; for large molecules the ultracentrifuge is used. See also mole.