Graham , Thomas

(1805–1869) Scottish chemist

Graham was the son of a prosperous Glaswegian manufacturer. He entered Glasgow University at the age of 14 and attended the classes of the chemist Thomas Thomson. Graham's father was determined that he should enter the ministry and on Graham's persistence with his scientific studies his father withdrew his financial support. To continue in chemistry Graham made his living through teaching and writing. In 1829 he became a lecturer at the Mechanics Institution and in 1830 he was elected to the chair of chemistry at Glasgow University. In 1837 he was appointed professor in the recently founded University College, London. He was the first president of the Chemical Society of London, and of the Cavendish Society, which he founded. In 1854 he was made master of the mint.

In 1829 Graham published a paper on the diffusion of gases. Observations on this subject had been made by Joseph Priestley and Johann Döbereiner, but it was Graham who formulated the law of diffusion. He compared the rates at which various gases diffused through porous pots, and also the rate of effusion through a small aperture, and concluded that the rate of diffusion (or effusion) of a gas at constant pressure and temperature is inversely proportional to the square root of its density.

In 1860 Graham examined liquids. He noticed that a colored solution of sugar placed at the bottom of a glass of water gradually extends its color upwards. He called this spontaneous process diffusion. He also noticed that substances such as glue, gelatin, albumen, and starch diffuse very slowly. He classified substances into two types: colloids (from Greek kolla, glue), which diffuse only slowly, and crystalloids, which diffuse quickly. He also found that substances of the two types differ markedly in their ability to pass through a membrane, such as parchment, and he developed the method of dialysis to separate them. Graham is regarded as the father of modern colloid science, and many terms that he invented, such as sol, gel, peptization, and syneresis, are still in use. Other work done by Graham includes research into phosphorous acids, the water of crystallization in hydrated salts, and the absorption of hydrogen by palladium. Graham was an excellent and successful teacher.