William Henry was born in Manchester, England on December 12, 1775. He was the son of Thomas Henry an apothecary and a founder of the Manchester Literary and Philosophical Society. Henry's early education took place at the Manchester Academy and he was apprenticed to Thomas Percival, a physician. As a boy he suffered an injury, caused by a beam falling on him, which left his growth stunted and caused pain. Because of the injury Henry would later abandon medical practice and instead devote his time to laboratory research. Dr. Percival had poor eyesight and was prone to headaches so he had Henry read to him. After a five year apprenticeship Henry went to Edinburgh University, where he studied medicine. While at Edinburgh he also attended the chemistry lectures of Joseph Black. He attained his M.D. in 1807.
While studying medicine Henry was also doing chemistry research. At the time it was believed that all acids contain oxygen and Henry attempted to remove oxygen from muriatic (hydrochloric) acid by electrocution. He was of course unsuccessful. When in 1810 Humphrey Davy proved that muriatic acid contained only hydrogen and chloride, Henry supported him, publishing a paper with further evidence in 1812. In 1802 he published an experiment where he measured the amount of dissolved gas in a liquid at different temperatures he showed that as the temperature drops the amount of dissolved gas increases.
He is most famous for discovering that the amount of a gas dissolved in a liquid is proportional to the partial pressure of the gas above the liquid. This is known as Henry's law. An example of how this law applies can be seen in canned or bottled carbonated soda. Before the can or bottle is opened the gas over the liquid is almost all carbon dioxide and the liquid contains dissolved carbon dioxide. When the can or bottle is opened the carbon dioxide over the drink is released and bubbles of carbon dioxide appear in the drink. As the partial pressure above the liquid is lowered (when the can or bottle is opened and exposed to the air) the dissolved carbon dioxide in the drink comes out of solution, producing bubbles. If the bottle or can is left to go to equilibrium almost all of the carbon dioxide will leave the liquid, and the soda will go flat.
Henry won the Copley Medal in 1808 and was elected a fellow of the Royal Society in 1809. In 1801 he published "An Epitome of Chemistry", later renamed "The Elements of Experimental Chemistry", which went through eleven editions and was last published in 1829.
He died on September 2, 1836.
"William Henry" in The Dictionary of National Biography; Leslie Stephen and Sidney Lee, Editors; Macmillian Compan; 1908
Thronber, Craig; "Thomas Henry, FRS and his son William Henry, MD, FRS, GS" at thronber.net
William Henry Wikipedia Entry