After research on the thermal expansion of air and unsaturated water vapor, Volta devoted himself between 1792 and 1796 to research on the density and tension of saturated vapors and their dependence on temperature. These results, obtained when the scientist was particularly engaged in the debate with Galvani over the alleged animal electricity, were also not sufficiently publicized, and he was not given credit for some important findings subsequently obtained by other scientists.
In the postscript to a letter to Vassalli dated October 27, 1795, published in Br. Ann., Vol. XI, 1796, p. 127, and in Ant. Coll., Vol. III, p. 381, the results obtained up to that point were summarized. These same results were obtained by Dalton in 1801 and are now reported in texts under his name.
VOLTA
DALTON
As can be seen, they are identical; moreover, with regard to the second law, we observe, as Polvani has clearly pointed out, ‘that while Volta’s law concerns both vapour pressure and density, Dalton’s law concerns only pressure: furthermore, while the former comes from a theoretical interpretation of the increase in tension, and leads to separating the effect due to the increase in density from that due to the increase in elastic stress, Dalton’s law consists purely of a statement of experimental facts’.
