Hydrochloric Acid and Methjletlicr. 59o 



Friedel and myself far below 100° may be ascribed to pure 

 mixing, or whether these too are influenced by the same 

 forces. I believe these doubts to be unfounded. Whatever 

 we may think the molecular condition of the mixtures to be — ■ 

 whether we assume the formation of double molecules or not — 

 the essential difference between the progressive chemical 

 reaction which gradually changes the condition and the 

 character of the mixtures on the one side, and the forces 

 which bring about the immediate equilibrium on the other, 

 caunot be denied. An equally distinct contrast exists between 

 formation of liquid in a single substance, even with association 

 of molecules, and irreversible polymerization. At the same 

 time it is possible that there may be some connexion between 

 the strong affinity at low and the action at high temperatures. 



The chief results arrived at are the following : — 



1°. The mixtures have a minimum vapour-pressure in 

 accordance with what could be derived from Friedel's experi- 

 ments. This minimum exists up to the critical condition. 



2°. Addition of hydrochloric acid raises the critical tem- 

 perature of methylether. For the reasons explained above, 

 the complete relation between critical temperature and pres- 

 sure could not be obtained. 



The results are represented in the figure, page 596. The 

 curves were completed in the part of the diagram where 

 observations were impossible by hypothetical pieces. The 

 general character of the diagram seems beyond doubt. It 

 shows how the mixtures as expected combine a maximum 

 critical temperature (at^L) with the minimum vapour-pressure 

 and in what manner the minimum curve meets the plaitpoint 

 curve at B. As was proved by van der Waals*, the two 

 curves touch each other at B, and the plaitpoint curve is 

 continuous at A. According to principles laid down by me 

 beforefthe mixtures will have retrograde condensation of the 

 first kind between C x and B, of the second kind between B 

 and A, and of the first kind between A and C 2 - 



The diagram agrees generally with one obtained a priori 

 for a mixture with minimum vapour-pressure by Hartman J. 

 It bears to a high degree the internal evidence of correctness, 

 and it can hardly be doubted will be confirmed when a 

 different representative of the type without chemical action 

 is examined: 



Another peculiarity of the figure worth noticing is the 



* Van der Waals, Kon. Ah. Amsterdam, Mei 25, 1895. 

 f Kuenen, Communications, Leiden, no. xiii. 1894; Phil. Mag 1 , xl. 

 p. 189. 



\ Hartman, Dissertatie, Leiden, 1899. 



! 



