Systems, poly variant, indifferent states

We met these theorems in studying the properties of states of uniform composition (chap. XVIII, 6) we shall now examine them in a more general form as a property of all static indifferent states in a poly variant system. 

We have already seen that all the states of a mono variant system are indifferent states. On the other hand, if a poly variant system is in an indifferent state, then its properties are in many ways analogous to those of mono variant systems. 

In the same way, for an indifferent state of a closed poly variant system, the temperature is sufficient to determine p and the composition of the phases, but not the masses of the individual phases. Furthermore, as we have seen, the law governing the variations hp and hT along an indifferent line, are of just the same form as the law which relates Sp and ST along the equilibrium states of a monovariant system. However, a profound difference is apparent between monovariant systems, and indifferent states of a pol3rvariant system when we consider the possibility of a closed system moving along the line of indifference. A closed mono variant system can clearly traverse its indifferent line, for this is simply its equilibrium line on the other hand, for a polyvariant closed system the ability to move along the indifferent line is exceptional as we shall now proceed to show. 

Case 2 w>2. A poly variant closed system of the second category cannot in general achieve an indifferent state although it may reach an indifferent point if the initial masses instead of being taken at random, are chosen correctly. 

---