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Graham, Thomas

gas diffusion glasgow metal

(1805–69) British physical chemist; studied passage of gases, and dissolved substances in solution, through porous barriers.

Son of a Glasgow manufacturer, Graham studied science in Glasgow and Edinburgh, despite his forceful father’s desire that he should enter the church. He held professorships in Glasgow and London, and became a founder of physical chemistry, and first president of the Chemical Society of London (the first national chemical society). One part of his work deals with the mixing of gases separated by a porous barrier (diffusion) or allowed to mix by passing through a small hole (effusion). Graham’s Law (1833) states that the rate of diffusion (or effusion) of a gas is inversely proportional to the square root of its density.

The density of a gas is directly proportional to its relative molecular mass, M . So if the rate of diffusion of one gas is k A and its density d A , and that of a second gas k B and d B , it follows that: Diffusion methods were used in 1868 to show that ozone must have the formula O3 ; and more recently were used to separate gaseous isotopes.

Graham studied phosphorus and its oxyacids (which led to the recognition of polybasic acids, in which more than one hydrogen atom can be replaced by a metal); and he examined the behaviour of hydrogen gas with metals of the iron group. He found that H2 will pass readily through hot palladium metal and that large volumes of the gas can be held by the cold metal.

His work on dialysis began the effective study of colloid chemistry. He found that easily crystallizable compounds when dissolved would readily pass through membranes such as parchment, whereas compounds of a kind which at that time had never been crystallized (in fact, of high relative molecular mass, such as proteins) would not dialyse in this way. This gives a method (today using polymers such as Cellophane rather than parchment) for separating large, colloidal molecules from similar compounds; this is useful in biochemistry, and in renal dialysis, where the blood of a patient with kidney failure is purified in this way.

Graves, Earl G. - Overview, Personal Life, Career Details, Social and Economic Impact, Chronology: Earl G. Graves [next] [back] Graham, Katherine - Overview, Personal Life, Career Details, Chronology: Katherine Graham, Social and Economic Impact

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