276 



which reduces to 



MOREY 



ART, G 



iA'R' - A"R" - A"'R"') 



dp 



dt 



mi" rrii" m" 

 m{" m^" m,'" 



IV IV IV 



mi Mi W3 



(A'V'-A"V"-A"'V"') 



mi" m-l' m" 

 m{" mr mz"' 



IV IV IV 



mi m2 mz 



or 



^ A'R' - A"R" - A"'R"' 

 dt ~ A'V - A"V" - A"'V"' ' 



Similarly, the relation between the variations of p and t in the 

 second of the above univariant equilibria, P' + P" + P"' + 

 P^, reduces to the same expression. It will be observed that the 

 coefficients A', A", A"' are those that occur in the reaction 

 equation 



A'P' = A"P" + A"'P"'. 



Hence we see that whenever three phases lie on a straight line 

 in the composition diagram, the p-t curves of all ternary 

 equilibria containing these three phases coincide with each other 

 and with the p-t curve of the univariant binary equihbrium 

 between the three phases alone. 



27. Equilibrium, K20-2Si02-H20 + KiO-SSiO^ + Solution + 

 Vapor. We will now consider the application of our equation 

 to a different type of equilibrium between two soUds, liquid and 

 vapor. Consider the equilibrium, K2O • 2Si02 • H2O + K2O • 2Si02 

 + L + V (curve 76 + 7c). In the concentration diagram 

 the course of this equilibrium is the curve Q2Q4, the boundary 

 curve between the fields of K2O -28102 and K2O -28102 -1120. 

 Since the two solid phases and vapor lie on a straight line, the 

 equation becomes 



dp^ _ Aivi iv' - v") - Aui (v" - 77") 

 dt ~ A2VI W - 2;") - Am {v" - v")' 



in which P' and P" represent K20-2Si02 and K2O -28102 •H2O, 

 respectively. This is the equation of the dissociation-pressure 



