Joseph Black

Joseph Black was born in Bordeaux in 1728 to a Scottish-Irish wine merchant and educated in Belfast, Glasgow, and Edinburgh. He became professor of medicine and chemistry at Glasgow and later at Edinburgh, where he was a central figure of the Scottish Enlightenment and a renowned, meticulous lecturer.

Black's earliest fame came from his chemical work on 'fixed air' (carbon dioxide), which he showed was produced by combustion, respiration, and the action of acids on carbonates, and which behaved as a distinct gas — among the first demonstrations that air is not a single substance. This work helped open the path to modern pneumatic chemistry.

His enduring contribution to thermodynamics was the discovery, in the 1760s, of two distinct quantities. He recognised that different substances have different capacities for heat — what we now call specific heat capacity — by observing that equal masses given equal heat reach different temperatures. And he discovered latent heat: ice absorbs heat while melting without any rise in temperature, and water absorbs still more on boiling. He founded the method of mixtures, the calorimetric technique that turned heat into a measurable quantity.

Black's ideas had immediate practical consequence. He was a friend and mentor to James Watt, and his understanding of latent heat informed Watt's analysis of the steam engine's efficiency. Black died in Edinburgh in 1799, his careful experimental style having shaped a generation of chemists.