644 



Prof. J. P. Kueiien on (Le 



The t^vo types are represented in the v-.r diagrams figs. 2 

 :jnd 3 ; a and h indicate tlie liquids and c the vapour. Let 

 ns now consider the behaviour of the mixtures under 

 isothermal compression and expansion ; suppose that the 



Fii 



Fvi. 3. 



liquid a is present in the tube with the vapour c, and let the 

 volume be changed ; this change may bring about the appear- 

 ance o£ the second liquid b, and the diagrams show under 

 what conditions. 1£ the mixture is o£ the first type (fig. 2), 

 the second liquid can only appear on compression, not on 

 expansion ; if the mixture belongs to the second type (fig. 3), 

 it can only appear on expansion. 



Now, with a mixture containing a comparatively small 

 amomit of methyl -alcohol, it was observed that by compression 

 the heavier liquid b (methyl-alcohol containing propane) 

 separated out in small drops from the lighter liquid a (propane 

 containing methyl alcohol) ; it follows that these mixtures 

 belong to the first type, and that the three-phase pressure 

 must be larger than the vapour- pressure of propane. 



On heating, an upper critical temperature of the liquids 

 was attained, where the two layers become identical; the 

 temperature lies at 21°'15; at this point the three-phase 

 equilibrium comes to an end. So far these mixtures resemble 

 mixtures of phenol and water, and also, as we shall see, those 

 of pentane and hexane with methyl- alcohol, but the influence 

 of pressure is different. The approach of the two liquids and 

 their meeting in a critical point may be brought about in two 

 perfectly distinct ways, viz. either by the withdrawal of the 

 fc^aturation-curve for the liquids inside the vapour-liquid curve 



