( S3 ) 



Physics. — TIte composition and the volume of the coexisting vapour- 

 and liquid-phases of mixtures of Meihijlchloride and Carbonic 

 acid. By Ch. M. A. Hartüak {Communication N''. 43 from the 

 Physical Lahoratory at Leiden^ by Prof.H. Kajieulingh Onnes). 



§ 1. Vax der Waals' theory of mixtures has already given rise 

 to numerous observations. Kuexex f. i. has determined the isother- 

 mal lines for three different mixtures of methylchloride and carbonic 

 acid in the gaseous phase in order to construct the «/^-surface up to 

 the border-curve for different temperatures and to obtain data about 

 the values of 01,2 and ^1,3. 'J'he phenomena in the neighbourhood 

 of the plaitpoint have also been investigated by him for different 

 substances. Through this the shape of the connodal lines in the 

 neighbourhood of the plaitpoints has become fairly well known. 



It was very desirable that now also a first plait crossing the ip- 

 surface from one side to the other should be traced experimentally 

 with special indication of the coexisting phases. If at a given 

 temperature the composition and the density of these phases are 

 known we may draw the projection of the connodal line in the x-v 

 plane and in this figure we may draw the projections of the tangents 

 which unite the coexisting phases on the surface. 



To obtain the data required for this has been the purpose of this 

 investigation. I have chosen methylchloride and carbonic acid for 

 substances because many data about the mixtures of these two have 

 already been gathered by Kuexen. 



§ 2. Fig. 1 may serve to explain the principle of 

 the method of investigation that has been followed. 



The coexisting phases are contained in a wide reser- 

 voir B. At the upper end of the reservoir we may 

 isolate a definite volume of the vapour- phase by 

 shutting the cock ^i and draw it off by means of the 

 cock i?2 and receive this above mercury in a common 

 gas tube. The quantity of this is found by measuring 

 the volume, pressure and temperature of the gas and 

 the composition is found by having the carbonic acid 

 absorbed by potash. 



In the same way we may isolate a definite volume 

 of the liquid-phase at the lower end of the reservoir. 

 The volumes of the liquid-space A and of the 

 vapour-space B have been determined by measuring 

 the volume of oxygen which they can contain at high 

 pressure. 



6 

 Proceedinors Roval Acad. Amsterdam. Vol. I 



51 



