( 609 ) 



observations of Young of isopoiitaiie Proc IMiys. Soc. LoihIoh 181)4/95, 

 p. 613, liowGvci', a deviation as foimd ahove for carlxni dioxide 

 cannot he derived. 



It maj' be that some connection exists between the above men- 

 tioned disturbance in the saturation pressure in the immediate neigh- 

 bouihood (»f the critical point of carbon dioxide and a disturbance 

 in the observations of Comm. N". 88 of the densities of saturated 

 liquid and vapour of carbon dioxide. Plate I represents these densities 



dii,j and (leap, expressed in the theoretical normal density. ^ {(luq-\- dvap) 



is also represented. The straight line is the line which was drawn 

 for the determination of the critical volume after the method of the 

 rectilinear diameter of Caillktct and Matihas in Comm. N". 88 

 (comp. Comm. N". 88 p. 574). The middle of the chord belonging 

 to 30.' 8 lies clearly below this line. If for the determination of the 

 rectilinear diameter only the three points at lower temperature are 

 nsed, the ditference is much larger. If this deviation cannot be 

 ascribed to an error of observation, it would follow hence that the 

 diameter of Caillktkt and Mathias for carbon dioxide shows a 

 curvature in the immediate neighbourhood of the critical point ^). 

 7^)8 indicates the critical density which in Comm. N". 98 (Kamerlingh 

 Onnes and Fabus) was derived from determinations less than 0.°002 

 deg. below the critical temperature. If we might assume that the 

 carbon dioxide of Comm. N". 98 and that of N". 88 possessed the 

 same degree of purity, an assumption to which the agreement between 

 the critical temperatures entitles, and also tliat the ditference in the 

 methods of density determination has not gi\en rise to a systematic 

 dilfe-i'ence, then the situation of the ytoiui /v^s would contirm the 

 curvature of the diameter in the neighboui'hood of the critical point. 

 A similar disturbance as we remarked above for the saturation 

 volumes of carbon dioxide in the immediate neigbourhood of the 

 critical point, cannot be derived either from Young's observations of 

 iso|)entane (comp. Proc. Phys. Öoc. London 1894/95 p. 636) or from 

 tliose of normal pentane (Trans. Chem. Soc. 71 (1897) p. 455), 



1) This cutvature is in another sense than tlie curvature found by Kuenen and 

 RoBsoN, (Phil. Mag. (G) 3 p. (1902) p. 624) at lower temperatures in the diameter 

 for carbon dioxide and which agrees witli the general rule given by Young (Phil. 

 Mag. (5) 50 (1900) p. 291) about this curvalure^at lower temperatures in con- 



nection with tlie vahie of and tlie slope of the diameter as compared with 



Phv 



the temperature axis. 



