Prout, William, 1785–1850, English chemist and physician. Prout's hypothesis, advanced in 1815–16, suggested that atomic weights of elements are multiples of that of hydrogen and that elements are formed by a condensation or grouping of hydrogen atoms. Later work on the determination of atomic weights showed that part of the hypothesis does, in general, apply. Prout won contemporary renown for his demonstration (1823) of the presence of free hydrochloric acid in the gastric juice of the stomach. He wrote many papers on the chemistry of the blood and urine.