( G40 ) 



(for in the equation is put x s = 0) than the liquid. Or in other 

 words, as we said above, the points sought can only present them- 

 selves in the three phase line with the least volatile component as 

 solid substance 1 ). However, whether those points will occur, depends 



on the value which Urn ( — I will get. If this value may be put 



\JflJx — 



= infinite, we get for x = : 



dp _m — t] s 



dT vi — v s 



so equal to the slope of the melting-point curve. So we must have 

 both pressure and temperature maximum, at least when the solid 

 substance expands on melting. This was the purport of the above 

 cited remark of van der Waals about ether and anthraquinone; if 



however (--) may not be put infinite, this conclusion is no longer 



valid ; it then depends on the value which : 



V» — V s {VI — V s ) 



SB I 



assumes for x = whether there exists a temperature maximum 



,v 

 or not; if the difference in volatilitv, so — , should not be so large, 



sbi 



that this expression becomes negative at the limit, the maximum 



does not occur, even when v s ^> Vi . 



The question whether such a maximum will occur in many systems, 



cannot be answered with certainty for the present. For this many 



data would be required, which we have not at our disposal as yet ; 



it is, however, possible to show the probability that only in very 



extreme cases the volability of the components will be so diversified, 



that a temperature maximum is to be expected. For this maximum 



to be just present, viz. in the triple point of the solid component, it 



is evidently required that : 



Xo_ vi — v s __ 

 sb i v —v s 



Now the first datum w r e should want, would be the variation of 

 volume during melting. It seems, however, that only a few data have 

 been collected for this ; I have found some in Winkelmann's "Hand- 



*) If has of course been tacitly assumed here, that there is no maximum vapour 

 pressure; in that case the points in question could be found in both three phase 

 lines. 



