Charles Cagniard de la Tour

Baron Charles Cagniard de la Tour (31 March 1777 – 5 July 1859) was a French engineer and physicist. Charles Cagniard was born in Paris, and after attending the École Polytechnique became one of the ingénieurs géographiques. He examined the mechanism of voice-production, invented a blowing machine and contributed to acoustics by inventing an improved siren. He also studied yeast.

In 1822, he discovered the critical point of a substance in his gun barrel experiments. He sealed a flint ball in a sealed gun barrel filled with fluids at various temperatures, and rotated it to hear the splashing sound as it hit the liquid surface. He observed that above a certain temperature, there is no splashing sound. Above this temperature, the densities of the liquid and gas phases become equal and the distinction between them disappears, resulting in a single supercritical fluid phase. After this discovery, he performed quantitative measurements of the critical point of several substances such as water, alcohol, ether and carbon bisulphide.

He was made a baron in 1818, and died in Paris. Despite several claims to the contrary, no portraits of Baron Cagniard de la Tour exist.