Definition of Graham's law in US English:

Graham's law

  • A law stating that the rates of diffusion and effusion of a gas are inversely proportional to the square root of the density of the gas.

    • ‘Since the rate of diffusion is determined by the average molecular velocity, Graham's law for diffusion could be understood in terms of the molecular kinetic energies being equal at the same temperature.’
    • ‘Based on his experiments with density he formulated Graham's law of effusion or diffusion which states that the rate of effusion or diffusion of gases at the same temperature and pressure are inversely proportional to their densities.’
    • ‘The law governing the rates of effusion of two gases is called Graham's law.’


Mid 19th century: named after T. Graham (see Graham, Thomas).