Graham, Thomas (1805-1869), a Scottish chemist. He was a pioneer in the study of the mixtures called solutions, and originated the branch of chemistry that deals with colloidal solutions. In 1834 he formulated Graham's Law, which states that the relative speeds of the diffusion of gases are inversely proportional to the square roots of their densities. Graham attended the universities of Glasgow and Edinburgh. He was a professor at the University of London, 1837-55, and was appointed master of the mint in 1855.