Pfeffer, Wilhelm Friedrich Philipp (1845–1920)

Apparatus for demostrating osmosis. In 1877 German physicist Wilhelm Pfeffer used a similar apparatus to make the first ever measurement of osmotic pressure and show that osmotic pressure varies according to temperature and the strength of the solute (dissolved substance).

German physiological botanist who was the first to measure osmotic pressure, in 1877. He also showed that osmotic pressure varies according to the temperature and concentration of the solute.

Pfeffer was born in Grebenstein, near Kassel, and studied at Göttingen. His first professorship was at Bonn 1873, and from 1887 he was at Leipzig.

Pfeffer made the first ever quantitative determinations of osmotic pressure, using a semipermeable container of sugar solution immersed in a vessel of water. He connected a mercury-filled manometer to the top of the semipermeable container. Pfeffer's work on osmosis was of fundamental importance in the study of cells, because semipermeable membranes surround all cells and play a large part in controlling their internal environment.

Pfeffer also studied respiration, photosynthesis, protein metabolism, and transport in plants. His Handbuch der Pflanzenphysiologie/Physiology of Plants 1881 was an important text for many years.