HETEROGENEOUS EQUILIBRIUM 



273 



the value of the numerator only. As the Uquid follows the 

 curve Q2Q1 the value of the last two terms of the numerator 

 soon becomes equal to the value of the first term. The numer- 

 ator then becomes zero, dp/dt becomes zero, and the curve 

 has a horizontal* tangent. It will be observed that such a 

 point of maxunum pressure is found on many of the p-t curves 



Fig. 8. The ternary system, H20-K20-Si02-Si02. A diagrammatic 

 representation of the p-l curves shown in Fig. 7; the numbers on the 

 curves are the same in Figs. 6, 7, and 8. The invariant points Q^a. 

 and Qih are shown as point Qs, and the curves 11 and 12 are not shown. 



representing univariant equilibrium between two soUds, liquid 

 and vapor in the system. It is most pronounced in the uni- 

 variant equilibrium, K2O • 4Si02 • H2O + SiOa + L -1- V. 

 On further increase in temperature the numerator becomes 



* Cf. footnote, page 257: -— takes the place of -7- of analytical 



at dx 



geometry. 



