292 MOREY ART. G 



ones in that in each the hquicl phase hes inside the triangle formed 

 by the coexisting soUd phases, and hence they are both eutec- 

 tics. At Qsa the coexisting phases are V + L + K2O • 4Si02 • H2O 

 + K2O • 2Si02 + K2O • 4Si02, and the Uquid hes within the triangle, 

 K20-4Si02 - K20-4Si02-H20 - K2O -28102; and, similarly, at 

 Qsb the liquid lies within the triangle, K2O -48102 -1120 — 

 K2O • 48102 — 8102. 8ince the liquid is symmetrically placed with 

 regard to the three solid phases, the four univariant equilibria 

 containing liquid will be stable in the same direction from the 

 invariant point. 8ince V - K2O • 48102 - H2O - K2O- 48102 

 is a straight line, the p-t curves of the equilibria, V + L + 

 K2O- 48102 -HzO + K20- 48102 and V + K2O- 48102 •H2O + 

 K20- 28102 + K20- 48102, will coincide metastably with each 

 other, and will coincide with the binary equilibrium, V + 

 K2O - 48102 - H2O + K20- 48102, the dissociation-pressure curve 

 of K20- 48102 -HaO. Hence the p-t curve of V + L + 

 K2O • 48102 - H2O + K2O- 48102, and therefore of all those con- 

 taining liquid, will go to higher temperatures and pressures. 8ince 

 only a small change in liquid composition will make K2O - 28102 

 - L - K2O • 48102 • 520 a straight line, with V and K2O • 48102 on 

 opposite sides, the curves, V + L + K2O - 28102 + K2O - 48102 • H2O 

 and L + K2O -28102 + K2O- 48102 + K2O • 48102 • H2O (the 

 condensed system), will coincide stable to stable, and with a 

 continuous change in the same direction in the liquid composi- 

 tion the curves will cross. 8imilar reasoning applied to the 

 phases, liquid, K20- 48102, and K20- 48102 -1120, shows that the 

 curve, V + L + K2O -28102 + KaO- 48102 -HaO, must lie 

 between the curves, L + K20- 28102 + K2O - 48102 - H2O + 

 K20- 48102 and V + L + K2O - 48102 • H2O + K20- 48102,- and 

 the latter curve must coincide with the dissociation-pressure 

 curve of K2O - 48102 - H2O, the equilibrium, V + K2O - 48102 • H2O 

 H- KsO- 48102. 



8imilar reasoning will serve to place the sequence of p-t 

 curves around the other eutectic, the invariant point Q^h- 

 The noteworthy feature of the curves proceeding from Qsb is 

 the rapid rise in pressure in the univariant equilibrium, V + L -F 

 K20- 48102 •H2O + 8102. 



In the preceding discussion it has been shown how the funda- 



