SN ee a ee a a eel er 
J. W. Gibbs—Equitibrium of Heterogeneous Substances, 448 
Equilibrium of masses in contact—The first problem to which 
the criterion is applied is the determination of the conditions 
of equilibrium for different masses in contact, when uninflu- 
enced by gravity, electricity, distortion of the solid masses, or 
capillary tensions. The statement of the result is facilitated 
by the following definition. : 
In addition to equality of temperature and pressure in the 
Masses in contact, it is necessary for equilibrium that the 
tential for every substance which is an independently varia- 
le component of any of the different masses shall have the 
imal variations in the composition and thermodynamic state 
of the different masses in contact. There are certain other 
Anything which restricts the free movement of the compo- 
nent substances, or of the masses as such, may diminish the 
number of conditions which are necessary for equilibrium. 
Equilibrium of osmotic forces.—I£ we suppose two fluid masses 
to be separated by a diaphragm which is permeable to some of 
the component substances and not to others, of the conditions 
of equilibrium which have just been mentioned, those will 
still subsist which relate to temperature and the potentials for 
€ substances to which the diaphragm is permeable, but those 
relating to the potentials for the substances to which the dia- 
phragm is impermeable will no longer be necessary. Whether 
the pressure must be the same in the two fluids will depend 
upon the rigidity of the diaphragm. Even when the dia- 
phragm is permeable to all the components without restriction, 
equality of pressure in the two fluids is not always necessary 
for equilibrium. : 
