Zsigmondy, Richard Adolf (1865–1929)

Austrian-born German chemist who devised and built an ultramicroscope in 1903. The microscope's illumination was placed at right angles to the axis. (In a conventional microscope the light source is placed parallel to the instrument's axis.) Zsigmondy's arrangement made it possible to observe particles with a diameter of one 10-millionth of a millimetre. He was awarded the Nobel Prize for Chemistry in 1925 for the elucidation of heterogeneity of colloids.

Zsigmondy was born in Vienna and studied at Munich. He stayed in Germany, becoming professor at Göttingen in 1908. Working at the Glass Manufacturing Company in Jena 1897–1900, Zsigmondy became concerned with coloured and turbid glasses and he invented a type of milk glass. This aroused his interest in colloids, because it is colloidal inclusions that give glass its colour or opacity. His belief that the suspended particles in gold sols are kept apart by electric charges was generally accepted, and the sols became model systems for much of his later work on colloids.

Using the ultramicroscope Zsigmondy was able to count the number of particles in a given volume and indirectly estimate their sizes. He showed that colour changes in sols reflect changes in particle size caused by coagulation when salts are added, and that the addition of agents such as gelatin stabilizes the colloid by inhibiting coagulation.