594 Prof. J. P. Kuenen on Mixtures of 



substances in question have the comparatively rare peculiarity 

 of a maximum in their boiling-points, and therefore a 

 minimum in their vapour-pressures. The object of the 

 investigation described in this paper was to trace this 

 minimum up to the critical region and to obtain a complete 

 pressure-temperature diagram for these mixtures. The theory 

 of mixtures developed by van der Waals* makes it very 

 probable that mixtures with a minimum vapour-pressure 

 combine this with a maximum in the critical temperatures. 

 They belong therefore to a type which so far has not been fully 

 investigated. 



It was of first importance during the investigation to keep 

 in view the possibility of irreversible chemical action, as this 

 would naturally entirely alter the character of the mixtures. 

 Friedel had not observed chemical action, but this did not. 

 give any warrant with regard to the behaviour of the mix- 

 tures at higher temperatures. 



In the course of the work it was found that even below 

 100° C. a chemical action takes place which increases in 

 rapidity as the temperature rises. The chief products of the 

 action are methylchloride and water. As the critical tem- 

 peratures of the majority of the mixtures lie above 100° an 

 important part of the research became impossible, and it 

 appeared that the combination of methylether and hydrochloric 

 acid is unsuitable for the purpose of exploring the complete 

 diagram for the type to which it belongs. At the same time 

 there are so very few representatives of this type which lend 

 themselves to an investigation in the critical region, that one 

 cannot afford to reject the combination altogether. It is pro- 

 posed shortly to undertake the investigation of mixtures of 

 acetone and chloroform. 



At first no chemical action had been noticed: it is possible 

 that the action depends upon the presence of moisture or other 

 impurities which happened to be present in smaller quantity 

 in the first experiments than in the later ones. It is more 

 probable, however, that the difference is due to the first 

 mixtures containing little acid, the later mixtures gradually 

 more and more. The velocity of the chemical action must 

 have been correspondingly smaller, and the results above 100° 

 obtained with these mixtures need not therefore be com- 

 pletely rejected, although no great value must be attached to 

 the actual numbers. It is possible that the existence of 

 chemical action at high temperatures may give rise to 

 some doubts as to whether the phenomena observed by 



* Kuenen, Phil. Mag. xliv. p. 199. 



