Na I ge i a. hin ee lee: 
a eC. ae 
PO a Tam a a Banh ha tt a a tS i hte ka 
J. W. Gibbs—Equilibrium of Heterogeneous Substances. 447 
nents is maintained constant, the pressure is in general a maxi- 
mum or minimum when the composition of one of the phases 
is such as can be produced by combining the other two. If 
the pressure is maintaitied constant, the temperature is in gen- 
eral a maximum or minimum when the same condition in 
regard to the composition of the phases is fulfilled. 
Stability of fluids.—A criterion of the stability of a homoge- 
neous fluid, or of a system of coéxistent fluid phases, is afforded 
by the expression 
e—tntpvo—pum—p/m, . . . —U,'m, (14) 
in which the values of the accented letters are to be determined 
by the phase or system of phases of which the stability is in 
question, and the values of the unaccented letters by any other 
phase of the same components, the possible formation of which 
is in question. We may call the former constants, and the lat- 
of change, and unstable with respect to the latter. In this case, 
It may be capable of continued existence in virtue of proper- 
