The Phase Rule and Its Applications

The Phase Rule and Its Applications is by Alexander Findlay. The text gives as a chief criterion that the same condition of equilibrium is reached from whichever side it is approached, and says that in this case water and vapour are in real equilibrium. For a solution, if the temperature is maintained constant, the same concentration will be obtained, no matter whether one starts with an unsaturated solution to which more solid is added, or with a supersaturated solution from which solid is allowed to crystallize out.

The text calls water in contact with hydrogen and oxygen at the ordinary temperature a case only of apparent equilibrium. The text says the mixed crystals which were thus obtained, and which van't Hoff called dilute solid solutions, showed great resemblance in their behaviour to ordinary liquid solutions, and obeyed the laws applicable to these. The text adds that these laws, however, can no longer be applied in the case of the concentrated solid solutions formed by the crystallization together of isomorphous substances, and known as isomorphous mixtures.