Thomas Andrews FRS FRSE (19 December 1813 – 26 November 1885) was an Irish chemist and physicist who did important work on phase transitions between gases and liquids.

[1] Andrews began a successful medical practice in his native Belfast in 1835, also giving instruction in chemistry at the Academical Institution.

Another important investigation, undertaken in collaboration with Peter Guthrie Tait, was devoted to ozone.

In the 1860s he carried out a very complete inquiry into the gas laws—expressing the relations of pressure, temperature, and volume in carbon dioxide.

[1][4][5] He concluded that... the gaseous and liquid states are only distant stages of the same condition of matter, and are capable of passing into one another by a process of continuous change.In Andrews' experiments on phase transitions, he showed that carbon dioxide may be carried from any of the states we usually call liquid to any of those we usually call gas, without losing homogeneity.