Continuing my great chemist series, my This Week in Science History (TWISH) post is on Thomas Graham. Graham was born in Glasgow Scotland, the son of a textile manufacturer, on December 21, 1805.  His father’s wish was for him to become a member of the clergy.  He defied his father and instead entered the University of Glasgow in 1819.  He was attracted to chemistry and stayed to receive his M.A. in 1826.

Graham is known for his work on diffusion.  His interest came from the work of chemist Johann Döbereiner who noticed that hydrogen gas escaped from a crack in a glass bottle quicker than the surrounding air diffused in to replace it.  In 1831, Graham was able to demonstrate experimentally that the rate of gas diffusion was inversely proportional to the square root of its molar mass and then describe this relationship mathematically (now known as Graham’s Law):

. . . where MW is the molecular weight of the gas.  This principle was used as the basis for the separation of ²³⁵U from ²³⁸U for the Manhattan Project.  Graham found similar behavior was obtained for liquids as well.  He discovered that some solutions are actually suspensions of particles and those particles can be too large to pass through a filter– otherwise known as colloids (milk is a good example).  Graham’s work on colloid separation served as the basis for the modern dialysis machine, which allows people in renal failure to live while awaiting a kidney transplant.