325 



210 

 205 

 200 

 195 

 190 



165 



5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 

 Hexane Molproc. 



85 90 95 



Nitrobenzene 



the type of the vapour pressure (resp. boiling) curves does change; 



with regard hereto the increasing difference in voiatiHty of the 



two substances is of dominating importance. 



It need not be argued that a fortiori no maximum pressure 



occurs in systems witli the lower members of the series, e.g. pentane 



and butane ^); these too will belong to the type retrogression. This 



is the more remarkable, because now the type: splitting up of the 



. dt 

 plait with a negative value of — , which was already considered 



dp 



rare on theoretical grounds, loses the greater part of its few 

 representatives. *) Kohnstamm's earlier opinion that this type would 

 hardly ever occur seems therefore to be right, in spite of his later 

 experiments which made him withdraw his statement. 



Inorganic Chemical Laboratory 

 university of Amsterdam. 



1) As has been found, indeed, for isopentane by Konowalow. 

 -) Gf. e.g. NiEUWKAMP's review, dissertation Amsterdam 1915. 



