In the
case of homogeneous bodies the critical elements have a simple, clear,
and precise sense; the critical temperature is that of the single
isothermal line which presents a point of inflexion at a horizontal
tangent; the critical pressure and the critical volume are the two
co-ordinates of this point of inflexion.
The three critical constants may be determined, as Mr S. Young and M.
Amagat have shown, by a direct method based on the consideration of
the saturated states. Results, perhaps more precise, may also be
obtained if one keeps to two constants or even to a single one--
temperature, for example--by employing various special methods. Many
others, MM. Cailletet and Colardeau, M. Young, M.J. Chappuis, etc.,
have proceeded thus.
The case of mixtures is much more complicated. A binary mixture has a
critical space instead of a critical point. This space is comprised
between two extreme temperatures, the lower corresponding to what is
called the folding point, the higher to that which we call the point
of contact of the mixture.
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