Mixed fluids may first of all be regarded as composed of a large
number of invariable particles. In this particularly simple case M.
Van der Waals has established a characteristic equation of the
mixtures which is founded on mechanical considerations. Various
verifications of this formula have been effected, and it has, in
particular, been the object of very important remarks by M. Daniel
Berthelot.
It is interesting to note that thermodynamics seems powerless to
determine this equation, for it does not trouble itself about the
nature of the bodies obedient to its laws; but, on the other hand, it
intervenes to determine the properties of coexisting phases. If we
examine the conditions of equilibrium of a mixture which is not
subjected to external forces, it will be demonstrated that the
distribution must come back to a juxtaposition of homogeneous phases;
in a given volume, matter ought so to arrange itself that the total
sum of free energy has a minimum value. Thus, in order to elucidate
all questions relating to the number and qualities of the phases into
which the substance divides itself, we are led to regard the
geometrical surface which for a given temperature represents the free
energy.
Pages:
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162