the Mutual Solubility of Liquids . 



195 



the pressure increases — here from the alcohol towards the 

 ethane on both sides of the vapour-liquid plait. The pressure 

 for mixtures containing so much alcohol that no second 

 liquid layer is formed must therefore be lower than the three- 

 phase pressure at the same temperature. The pressure of the 

 first mixture at 14°*95 C is 33*62 atmospheres (which would 

 have been 33*74 at 15°*1 C), and thus indeed slightly lower 

 than the corresponding pressure of the three phases at the 

 end of the condensation of mixture II. The pressure at 

 31° 95 C, on the other hand, is much higher than the corre- 

 sponding three-phase pressure. The explanation of this 

 divergence from theory is probably simply this : that near 

 the end of the condensation a second layer, which escaped 

 our notice, had actually been formed, and the high pressure 

 required was really a pressure on the two-liquid plait, and 

 not on the vapour-liquid plait. 



With rise of temperature the points b and c approach each 

 other. At 32°* 16 C., the critical temperature of ethane, a 

 plait-point appears on the surface on the ethane side. This 

 plait-point approaches cb, and at 35°'37 C. the two phases 

 become identical, and the plait-point disappears. Above 

 35°*37 there is only one plait left, the plait-point of which in 

 the case of methyl alcohol could not be reached, as the 

 pressure and temperature became too high. We will defer 

 further consideration of the phenomena above the critical 

 point to the cases of propyl and butyl alcohol, where the 

 second plait-point belonging to the liquid plait was thoroughly 

 investigated. 



The next three higher alcohols differed from methyl alcohol 

 in having a lower critical point. Ethane and ethyl alcohol, for 

 instance, at the ordinary temperature mix in all proportions. 

 At 31°*9 C. (Table V.) the liquid, after showing the charac- 



Table V.— Ethane and Ethyl Alcohol (I.). 



t. 



Vb- 





14-97 



32-97 

 P- 



Two phases. 



3190 



C. 46-25 



Three phases. 



31-95 



4634 





32-15 



46-49 





32-55 



46-90 





3485 



49-05 





3915 



53-23 





4067 



C. 5490 



" 



