85 



Considering, instead of the saturatioiK'nrvcs tlie boiling- point 

 curves, the same applies to these in general. Wo nin«t then replace 

 on the fonrpliase-cnrve the point of maximninten)[)eratnre by the 

 point of maximum pressure. In tig. 3 besides the point of maximum- 

 temperature H, also the point of maximum-pressure Q is drawn. 

 We imagine further that the saturationcurves are replaced in the 

 diagrams by boilingpointcurves. We then refind the rules 1, 2, and 

 3, with this difference, however, that increase of pressure must be 

 replaced by decrease of the boilingpoint and decrease of pressure by 

 increase of the boilingpoint. 



From each point of the four-phase curve proceed two saturation- 

 curves and two boilingpointcurves. When this solution is to be 

 considered as rich in water or as poor in water with respect to the 

 saturationcurves, it is also the same with respect to the boiling- 

 pointcurves. Only the solutions between the point of maximum- 

 [)ressure and the point of maximumtemperature make an exception; 

 these are rich in water when we consider the saturationcurves, 

 poor in water when we consider the boilingpointcurves. Now we 

 find : from a solution saturated with two solid substances the vapour- 

 pressure (along one of the saturationcurves) and the boilingpoint 

 (along the corresponding boilingpointcurve) change generally in 

 opposite direction. When, however, this solution is situated between 

 the point of maximum pressure and the point of maximumtemperature, 

 vapourpressure and boilingpoint change in the same direction. 



{To he continued). 



Physics. — ''On the thermodynamic potential as a kinetic quantity". 

 (First part). By Dr. H. Hulshof. (Communicated by Prof. 

 J. D. VAN DER Waals). 



(Communicated iu the meeting of April i24, 1914). 



In a communication published in These Proc. II p. 389 of Jan. 

 27 1900 ^) it has been set forth by me that in the capillary layer 

 the molecular pressure must have a different xalue in different 

 directions as a direct consequence of the attraction of the particles, 

 whereas the thermic pressure (the sum of the molecular and the 



1) I expressly call attention to this date, because some time after, this subject 

 was treated in the same way by a writer who had informed me of his own 

 accord that he was going to publish an article on this subject in the Zeitschrift 

 fur phys. Chemie, and that he should of course, cite my paper there, but who 

 has failed to do so. 



