( 222 ) 



and, as the slope increased still more, an important erosion. Bj 

 this erosion the Me use conld excavate a broad valley through the 

 Rhine-diluvium and deej) in the Upper Pliocene clay, in which, the 

 slope having somewhat decreased, probably already in the second 

 or great Pleistocene Glacial Epoch, there accumulated a mighty 

 deposit of gravel. 



Physics. — Contributions to the hioinlechje of van der Waals' if> 

 surface. IX. The conditions of coexistence of binary mixtures 

 of normal substances according to the law of corresponding 

 states. By Dr. H. Kamerlingh Onnes and Dr. C. Zakrzewski. 

 Supplement N". 8 to the communications from the Physical 

 Laboratory at Leiden. 



(GommuDicated in the meeting of February 27, 1904). 



1. The qraphical treatment of the conditions of coexistence. In this 

 paper where the theory of mixtures of van der Waals is illustrated, 

 as in the former contributions we have placed in the foreground 

 the law of corresponding states. 



The data required calculating van der Waals' ip-surfaces for all 

 temperatures may be defined in the following way from the point 

 of view of this law: 



1°. An equation of state agreeing with reality, must be given for 

 one normal substance over the whole range of temperatures and 

 pressures to be obtained, (comp. § 2). 



2°. For the different mixtures of the two substances considered, as 

 well as for these substances themselves, the deviations from the law 

 of corresponding states must be known (comp. ^ 3). 



3". We must know the critical temperature T.,h and pressure 

 Wrt of each mixture taken as homogeneous ^) with the molecular 

 proportion x of one of the components, derived from tlie law of cor- 

 responding states, as functions of those of the simple substances and 

 of X (comp. § 4). 



With these data at our disposal van der Waals' theory will teach 

 us all possible cases of coexisting phases of those substances if we 

 roll tangent planes over the if>surfaces of each pair of substances for 

 different temperatures. 



In the treatment of the problems concerning conditions of coexistence 



1) Whenever we speak of critical temperature, a maximum vapour tension etc. 

 of a mixture without more, we always mean "taken as homogeneous". 



