( 759 ) 



The stem b 4 (see PI, II Comm. N°. 69), on which the volume 

 U 4 is read, was 30 cm. long in order to enable us to determine 

 every time three points on (he isotherm which did not lie too near 

 each other 1 ). In others of our piezometers it was taken still longer. 



For the series II and III a piezometer of larger dimensions was used. 



The necessity of the use of a larger gas-volume for determinations 

 at densities higher than 120 times the normal has already been men- 

 tioned in § 19 of Comm. N°. 84. The volumenometer described there 

 was not used, but just as in Series I the normal-volume was deter- 

 mined in the piezometer itself. 



As in the preceding table the dimensions of the piezometer are 

 given here. 



In Series II the piezometer-reservoir had a volume of 10.343 cM 8 , 

 but for the rest it had the same dimensions as in Table III. 



To detect any escaping of gas during the measurements at high 

 pressure in consequence of leakages at the connections g t and g l 

 (see PI. II Comm. N°. 69), cylindric glass oil-trays were placed 

 round these couplings (see PI. I fig. 2) which enabled us to discover 

 immediately even the slightest leakage ; everywhere the oil-trays 

 rendered excellent services, but here they were of the greatest 

 importance for obtaining reliable results *). 



!) They may serve, inter alia, to give us information about the curvature and 

 the inclination of the isotherms at the middle point. 



2 ) Once the oil-trays near the couplings g x and g 2 rendered good services, 

 when before the determinations of Series III gas escaped in consequence of the 

 nut g 2 being imperfectly screwed on. From a determination of the normal-volume 

 made immediately afterwards, it proved to have changed so much that the previous 

 determinations had to be rejected. 



