Between these two temperatures an
isothermal compression yields a quantity of liquid which increases,
then reaches a maximum, diminishes, and disappears. This is the
phenomenon of retrograde condensation. We may say that the properties
of the critical point of a homogeneous substance are, in a way,
divided, when it is a question of a binary mixture, between the two
points mentioned.
Calculation has enabled M. Van der Waals, by the application of his
kinetic theories, and M. Duhem, by means of thermodynamics, to foresee
most of the results which have since been verified by experiment. All
these facts have been admirably set forth and systematically
co-ordinated by M. Mathias, who, by his own researches, moreover, has
made contributions of the highest value to the study of questions
regarding the continuity of the liquid and gaseous states.
The further knowledge of critical elements has allowed the laws of
corresponding states to be more closely examined in the case of
homogeneous substances. It has shown that, as I have already said,
bodies must be arranged in groups, and this fact clearly proves that
the properties of a given fluid are not determined by its critical
constants alone, and that it is necessary to add to them some other
specific parameters; M.
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