A Modified Phase Rule Equation

Abstract

I AM obliged to Mr. Copley for pointing out what appears to be an ambiguity in the use of the expression concentration in the definition of the restriction term of the modified phase rule. Naturally, in the case of unary systems, the restriction term refers to identity of the phases and for a system at the triple point, r = 0, since the phases are not identical. Accordingly, we have P + F + R = C + 2 r 3 + F + 0 = 1 + 2 0, which is correct. I made no reference to this simple example in my first communication because it is easily solved by means of the ordinary Gibbs equation.