Prout, William (1785–1850)

British physician and chemist. In 1815 Prout published his hypothesis that the relative atomic mass of every atom is an exact and integral multiple of the mass of the hydrogen atom. The discovery of isotopes (atoms of the same element that have different masses) in the 20th century bore out his idea.

In 1827, Prout became the first scientist to classify the components of food into the three major divisions of carbohydrates, fats, and proteins.

Prout was born in Gloucestershire and studied medicine at Edinburgh. He set up a medical practice in London and established a private chemical laboratory. From 1813 he wrote about and gave lectures in ‘animal chemistry’.

Studying various natural secretions and products, Prout became convinced that they derive from the chemical breakdown of body tissues. In 1818, he isolated urea and uric acid for the first time, and six years later he found hydrochloric acid in digestive juices from the stomach.

In his anonymous paper of 1815, Prout concluded, from the determinations of atomic weights that had been made, that hydrogen was the basic building block of matter. In 1920 Ernest Rutherford named the proton – the hydrogen nucleus, which is a constituent of every atomic nucleus – after Prout.

Prout also studied the gases of the atmosphere and in 1832 made accurate measurements of the density of air. The Royal Society adopted his design for a barometer as the national standard.