Thomas Andrews, (born December 19, 1813, Belfast, Ireland—died November 26, 1885, Belfast), Irish chemist and physicist who established the concepts of critical temperature and pressure and showed that a gas will pass into the liquid state, and vice versa, without any discontinuity, or abrupt change in physical properties. He also proved that ozone is a form of oxygen.
Following studies in Britain and Paris, he received a medical degree from the University of Edinburgh (1835). He was appointed vice president of Northern College in Belfast in 1845 and helped to prepare it for its reorganization as Queen’s College, Belfast (1849). He was professor of chemistry there from 1849 to 1879.