( •'^75 ) 



4. In tlie third place 1 will point out what I have already demon- 

 strated in a previous i)ablication '), that when the tension of a com- 

 pound is smaller at its melting point than that of the components, 

 a three phase curve may occur with a very peculiar shape, viz 

 with one minimum and two maxima. 



l^et us now consider the case that the melting point of this com- 

 pound lies above the critical temperatures of the components, tiien 

 the very peculiar phenomenon may present itself, that what occurred 

 once in the system ether and anthraquinone, is here to be realized 

 twice, and that the solubility curve which runs from one eutectic 

 point to the other, meets the plaitpoint curve four times, which 

 appears in the PT-projection tig. 3 as a four times repeated inter- 

 section of the three phase curve A,„B„-[-L-[-Gr and the continuous 

 plaitpoint curve bKLd in the points p, q, c[ and p' . 



It ai>jiears from the PT and TX-prqjections that for all possible 

 concentrations a range of temperature may be pointed out, within 

 which the solid compound can only coexist with a fluid phase. 

 When, however, which is conceivable, the portions cut out of the 

 three phase line have no range of temperature in common, the 

 temperature regions for solid -\- fluid, lie above each other, and so 

 we have no symmetrical phenomena for any temperature on both 

 sides of the line for A,„B„ in the PT-projection. 



The systems hydrogen-water and oxygen-water -belong to the type 

 ether-anthraquinone when the components are miscible in all propor- 

 tions. Each of these systems will then yield a point p and a point q. 

 Supposing, which is, however, highly improbable, that by the appli- 

 cation of a catalyser we could bring about equilibrium between 

 oxygen, hydrogen and water vapour at any temperature, we should 

 get a continuous three phase line for ice -J- L -]- G as is indicated 

 in fig. 3, and also one continuous plaitpoint curve. The equilibrium 

 with water, however, lying theoretically almost quite on the side of 

 water at lower temperatures, we should commit a practically un- 

 apjn'eciable error, when we tried to realize at these lower temperatures 

 the diagram drawn here b}' starting in one case from ice, reap, 

 water -\- hydrogen, and in another case from ice, resp. water -|- 

 oxygen. 



This example, however, is not suitable for illustration of the 

 assumed case, because for this purpose we require a compound 

 which appreciably dissociates at its melting point. I have only men- 

 tioned the system H^ — 0^ to show how remarkable this system is. 



It is very probable that systems are to be found, with which the 



') loc cit. 



40 



Proceedings Royal Acad. Amsterdam. Vol. VIII. 



