( 233 ) 



tions ail 

 suited to illustrate this part of the theory of van der Waals. 



The considerations, constructions and ligures given seem therefore 



RT 



is in the case of carbon dioxide and methylchloride a curve slightly 

 bent downwards. Fig. 5 shows how the liquid branch of the binodal 



If? 



line (the rim curve of the liquid part) — — - (comp. also the other 



It 



ligures) follows from tiie curve — ^^ and the curve ^oa-. 



As to the calculation of (f 'i[ it should be remarked that \>,nax 

 as function of t is known through the vapour tension law, and 

 hence also from the empirical equation of state i\.r?^, and that 



n n 



I )fdo =: j p(/o -|- p„,a.,. (i\,„^ — i\i^). Especially if i^/^ is small and 



IV/7 'Cvap 



B 

 hence ry„n large, (so that at the utmost — comes into consideration 



V 



for the deviation from the ideal gas laws) this, when at the same 



time neglecting t)/,-^, leads to an important shortening of the calculations. 



Neglecting entirely tlie deviation of the vapour phases from the ideal 



gaseous state and accepting for a simple substance % p»*'^^ = — / 



we return to the developments given by van der Waals in his theory 

 of the ternary mixtures ^) in which theory many problems about 

 the binary mixtures are developed more in detail. 



Physics. — ''Tlie determination of the conditions 0/ coexistence of 

 vapour and liquid phases of mixtures of gases at loiv tempe. 

 ratures." By Dr. H. Kamerlingh Onnes and Dr. C. Zakrzewskl 

 Communication N". 92 from the Physical Laboratory of Leiden 

 by Prof. H. Kamerlingh Onnes. 



(Communicated iu the meeting of June "2^, 1904), 



§ 1. Introduction. The two methods for the determination of the 

 molecular coexistence compositions ,vi and x^ of the liquid and vapour 

 phases of substances which are gaseous in normal conditions, it is 

 known, can be described as follows. Following the first method we 

 separate small (piautities from the two phases at a series of coexistence 



1) Proceedings, May 31, 1902, p. 1, sqq. 



