Graham’s law states that the diffusion rates of two gases through the same duct, at the same conditions of temperature and pressure, are inversely proportional to the square roots of their respective molecular weights. Chloridic acid and ammonia, the two gases employed in this experiment, pour into the center of a duct. When contact occurs they react and form white ammonium chloride fumes. In this way it is possible to determine the path taken by the two gases and their ratio used to estimate their density and molecular mass.
THEORETICAL – EXPERIMENTAL HANDBOOK