For other men withy the same name, see: Wiliam Henry (disambiguation).

William Henry (December 12, 1775—September 2, 1836) was an English chemist.

Henry was the son of Thomas Henry (1734-1816), an apothecary and writer on chemistry, was born at Manchester. He began to study medicine at Edinburgh in 1795, taking his doctor's degree in 1807, but ill-health interrupted his practice as a physician, and he devoted his time mainly to chemical research, especially in regard to gases. One of his best-known papers (Phil. Trans., 1803) describes experiments on the quantity of gases absorbed by water at different temperatures and under different pressures, the conclusion he reached (Henry's law) being that water takes up of gas condensed by one, two or more additional atmospheres, a quantity which, ordinarily compressed, would be equal to twice, thrice, &c. the volume absorbed under the common pressure of the atmosphere. Others of his papers deal with gas-analysis, fire-damp, illuminating gas, the composition of hydrochloric acid and of ammonia, urinary and other morbid concretions, and the disinfecting powers of heat. His Elements of Experimental Chemistry (1799) enjoyed considerable vogue in its day, going through xi editions in 30 years. He died at Pendlebury, near Manchester.