Searching for a name: the development of the concept of the critical point (1822-1869)/A la recherche d'un nom : le développement du concept de point critique (1822-1869)

Abstract

SUMMARY. — The origins of the concept of the critical point can be traced back to the work of baron Charles Cagniard de Latour who in 1822 had shown that there was necessarily a limit to the dilatation of a volatile fluid beyond which it would become a vapour, notwithstanding the pressure. It seems that Faraday was actually the only researcher before Andrews who had realized the full meaning of Cagniard de Latour's experimental results. Indeed, the careful study of his diary and of his correspondence with Whewell brings to the surface evidence that "Cagniard de Latour's point " was, for him, not just a point of "destruction " of the liquid state, but a point "at which the fluid and its vapour become one according to a law of continuity. " It was Andrews, however, who was able to show, in 1869, for the first time 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. Thus, the concept of the critical point, in a span of fourty-seven years, was gradually transformed from a concept that presupposed the discontinuity of the gaseous and liquid states, to a concept that implied the continuity of those states.