( 389 ) 



pressure-curve. In this case point D^ which lies on that branch of 

 the plaint-curve that originates in B above C, is the last of the 

 plait-poinls thnt may be realized if the phenomena of retardation 

 are excluded. From this follows, that howe\er much we may lower 

 the temperature, the pressure of the three phases will continue to 

 exist. The points between C and D^ marked on the curve, indicate 

 plait-points of such values of x, at which they lie above the derived 

 surface, resting on the connodal line which encloses the two separate 

 branches of the spinodal line. From the phrase of Kuenen and 

 RoBSON, p. 357 : "Oberhalb 35,37° ist nur eine Falte vorhanden, deren 

 Faltenpuukt wir bei Methylalcohol nicht erreichen konnten, well Druck 

 und Tempemtur zu hoch waren" seems to follow, that point D of 

 our figure 2 must not lie above C, but that it would have to be 

 taken more to the side of B. As there remain so many uncertain- 

 ties, it is to be regretted, that in the case of methylalcohol they 

 have not been able to carry out their investigation. We must not 

 attach greater value to fig. 2 than that it has led to the supposition 

 that the cause of the difference in behaviour for mixtures of ethane 

 and methylalcohol must be found in the smallne&s of the methyl 

 molecules ^). 



I shall avail myself of this opportunity to make the following 

 remark about what is really properly to be called "longitudinal plait." 



In a mixture of normal substances a relation may exist between 

 the quantities aj, «,3, oj' ^n ^'n and i-a, of such a nature that there 

 actually exist two plaits, each of which possesses a connodal curve 

 of its own. At a same temperature both may be proved experi- 

 mentally. Then the principal direction of the transverse plait is 

 // u-axis and the principal direction of the longitudinal plait is 

 // .r-axis. But in this case the plaitpoint of the longitudinal plait 

 lies on the side of the large volumes. This has been proved 

 theoretically by Prof. Korteweg in the special case of sym- 

 metry and a similar case has been worked out experimentally bv 

 Mr. VAN DER Lee. (Proc. Rdyal Acad. 1898). Theory has not yet 

 been able to decide whether this plait may be again closed if the 

 volumes are much smaller still, or whether it continues to diverge, 

 even when the limiting volumes are reached. If the latter should 



tip (Jp- 



1) The n-eometrical locus of the roiiits, for which — aud — is equal to 0, cannot 



dr> dü- 



teach anytbing about the plaitpoiuts of the real longitudinal plait. Moreover I do 



not share Mr. Kuenen's expectation that also for methylalcohol the plait is the same 



as for the following alcohols. I expect that the course of the plaitpoint-curve of a 



mixture of methylalcohol and ethane shows great resemblance to tliat of a mixture 



of water and ether. 



