182 Messrs. J. P. Kuenen and W. G. Robson on 



have regard to the compositions of the two liquids which are in 

 equilibrium. The most important of these are by Guthrie *, 

 Alexejewf, and quite recently Rothmund J. The paper 

 of the last named, which appeared after the completion of our 

 experiments, contains a very full account of former experiments 

 on the same subject. By these investigations the following facts 

 have been established. The mutual solubility of two liquids 

 changes considerably with temperature. In the large majority 

 of cases, the mutual solubility increases with rise of tempera- 

 ture, the two phases approaching each other and finally 

 becoming identical. Above the temperature at which this 

 occurs the liquids are consolute, i. e. they mix in all proportions. 

 In some cases, this temperature was not reached, but the 

 changes in composition tended to show that a further rise of 

 temperature would have made them also consolute. In other 

 cases, ether and water for example (Klobbie §), the change 

 of composition of the liquids was so small that no definite 

 conclusion could be arrived at. In several cases the mutual 

 solubility, instead of increasing regularly with rise of tempera- 

 ture, began by diminishing, i.e. the composition of the phases 

 receded from each other, but beyond a certain point they 

 approached again, and ultimately the phases coincided. In one 

 case (water and secondary butyl alcohol, Alexejew) the phases 

 first approached, then receded, and finally approached again 

 and coincided. It is different with diethylamine and water 

 (Guthrie ||), triethylamine and water (Guthrie and Roth- 

 mund), /3-collidin and water (Rothmund H), and also 

 with the bases of the pyridin and chinolin series and water. 

 For these mixtures the mutual solubility increases on lowering 

 the temperature, until at a certain temperature the phases 

 become identical ; below this temperature they are consolute. 

 What happens to these mixtures on their temperature being- 

 raised has not as yet been settled. 



In order to represent the behaviour of liquids with respect 

 to their mutual solubility, the temperature-composition 

 diagram is used. The curve in this diagram, which we shall 

 call the solubility-curve, gives the compositions of the two 

 liquids which are in equilibrium at each temperature. 

 Orme Masson** approached the problem from the theoreti- 

 cal side ; he was one of the first to point out the resemblance 



* Guthrie, Phil. Mag. 5th ser. xviii. pp. 22, 495. 



t Alexejew, Wied. Ann. xlviii. p. 305. 



J Rothmund, Zeitschrift Phys. Chem. xxvi. p. 433. 



§ Klobbie, Zeitschrift Phys. Chem. xxiv. p. 615. 



|| Guthrie, I. c. % Rothmund, I. c. 



** Orme Massori, Zeitschrift Phys. Chem. s'\i. p. 500. 



