GRAHAM, THOMAS (1805-69). An English chemist, born in Glasgow. Having studied at Glasgow and Edinburgh, he became, in 1830, pro fessor of chemistry at the Andersonian Univer sity, and continued in that office till 1837, when he succeeded Dr. Turner in the chemical chair of University College, London. In 1855 he was ap pointed master of the mint, and resigned his professorship. Graham is best known for his researches on the diffusion of gases and of sub stances in solution. His experiments, carried out with the aid of very simple apparatus, fur nished valuable data, which have proved of great importance in the development of the modern theory of solutions. In studying solutions, he found that the velocity of diffusion varies with the substance in solution, and depends to a great extent on the temperature at which the liquid is kept. He found that amorphous substances like albumen, gum arabic, silicic acid, ferric hydroxide, etc., which he designated by the term colloids, dif fuse very slowly, and are incapable of passing through parchment paper or animal membranes, while substances like sugar, the mineral acids and their salts, etc., which he termed crystalloids, dif fuse more or less rapidly and pass freely through membranes. He was thus led to the discovery of the analytical method known as dialysis. To separate by this method a crystalloid from a colloid, the solution containing both is placed in a suitable vessel, and is separated from a volume of pure water usually by parchment paper. Part
of the crystalloid then passes out of the solu tion into the pure water, while the colloid is stopped by the membrane. If the water, now containing some of the crystalloid, is replaced by a new quantity of pure water, some more of the crystalloid diffuses out of the solution con taining the mixture. By repeating the operation several times, a solution is finally obtained which contains practically nothing but the pure colloid. Graham carried out numerous other classical re searches in chemistry, including investigations of the acids of phosphorus, the constitution of sul phates and oxalates, etc. His researches were published in the form of original memoirs, com prising in all sixty-three papers on various sub jects. In addition to these memoirs, he brought out an excellent treatise on chemistry, which has passed through several editions, and was repub lished in this country and translated into Ger man. He also edited the Chemical Reports and Memoirs of the Cavendish Society in 1848. Graham was the first president of the Chemical and the Cavendish societies, was a fellow of the Royal Society, and an honorary member of many foreign scientific bodies. He was likewise fre quently placed by the British Government on important scientific commissions. See DIFFU SION; COLLOIDS; CHEMISTRY.