( 1«3 ) 



pressure of 100 atm., as the equation is not sufficiently approxima- 

 tive, and because Mr. Amagat himself comes to the conclusion, 

 that the deviation found does not exceed the possible errors of 

 observation. It were desirable that similar experiments were made 

 with equal volumes of substances which differ much in physical 

 properties. In testing, the equation (4) should be replaced by another 

 which would hold with a higher degree of approximation. If 

 the volumes j^, , i\^ and v show a marked difference, the term 

 a, 4- «3 — 2 «J ^ should be replaced by : 



v.v. 





9 ~1 2 



1 2 



an expression, which at a feeble density may be considered as equal 

 to a^ |- a„ — 2aj„, but which approaches 





if the density increases. 



We have no right to expect, that the value of Ay will remain 

 perfectly constant at various degrees of density (which would follow 

 from the approximative equation), and at any rate the reservation 

 is to be made, that always either two gas-phases or two liquid- 

 phases are to be mixed. We may however expect, that the value 

 of Lo will keep within certain finite limits, and that therefore, that 

 which may seem large as compared to two small volumes (liquid 

 volumes), may be neglected if compared with very large gas volumes. 



Mr. KuENEN (Dissertation 1892, Leyden) has made observations 

 from which the quantity Au may be determined for mixtures of 

 of CO, and CH3 CI and has found it positive. It is to be regretted 

 that he has not tried to determine the value of Ay, but that he 

 gives the increase of pressure, which is to be applied, in order to 

 reduce the volume of the mixture to the sum of the volumes of 

 the componeuts. Intricate calculations are necessary for findinf our 

 result confirmed, namely that Au is not 0, but that it has a value 

 of the same order of greatness all tiirough the course of the isotherme. 

 If he had restricted himself to the determination of Ay, he would 

 undoubtedly have come to the conclusion, that Ay is quasi-constant 

 and he might have given an approximative rule, which I now feel 

 obliged to ascribe to Mr. Amagat, though Amagat's rule Ay = 

 must be replaced by Ay is nearly constant. 



13 



Proceediugs Rovnl Acad. Auiaterdaui. Vol. I, 



