884 



V. Determination oj the po'mta of Ix'jjlnnimj condensation. 



1. Apparatus. 



The apparatus used for this purpose was arranged in tlie manner 

 of a constant volume gas-tliermometer. Its vessel liad a volume of 

 about 142 cc. and was provided at tlie lower end with a small 

 appendix 8 mms. long in wliieli the liquid gas collected. In order 

 to make sure that equilibrium was attained the liquid could be 

 stirred by means of a small steel ball, which on closing a current 

 was drawn up in the field of a small electro-magnet with pole- 

 pieces cut at 45°. In calculating the changes of volume of the vessel 

 the coefficient of expansion was taken as O.ÜOÜ02J2, the mean of 

 the results obtained by Travers, Skntf.r and .Iaquerod ^) and bj 

 Kamerlinüh Onnes and Heuse ') for Thiiringen-glass between 0° and 

 —190°. 



The measurement was conducted as follows : a measured quantity 

 of gas was transferred to the vessel and the pressure read at a 

 definite temperature; a second quantity of gas was then measured 

 and transferred to the vessel, and the pressure was read again, 

 etc. etc. until condensation set in. The vapour-pressm-e was then 

 measured at increasing densities of the vapour. 



For a convenient measurement of the quantities of gas which were 

 added, the manometer-tube on the vessel-side was provided with a 

 scale-division and had been accurately calibrated. For the reading 

 of the pressures a cathetometer was sometimes used, sometimes a 

 vertical comparator with steel measuring-rod. In the latter case the 

 accuracy' is smaller, but not smaller than about 0,1 mm. 



2. The measurements. 



pv 

 For each mixture at three difiereni temperatures was now 



determined as a function of the pressure, where p is the pressure 

 of the mixture in mms. and v the volume of the gas in the vessel, 

 divided by the theoretical normal volume of the same quantity. ') 

 The point, where this curve shows a discontinuity, is the point of 

 beginning condensation in question. 



For each quantity of gas which was added the normal volume 

 was each time calculated ; this volume was diminished by the quantity 

 contained in the dead space and the capillary in order to obtain 

 the quantity of gas in the vessel. 



1) Travers, Senter and Jaquekod. Phil. Trans. A 200. p. 138. 

 -) H. Kamerlingh Onnes and W. Heuse. Coram. Leiden No. 85. 

 3) H. Kamerlingh Onnes and W. H. Keesom. Enc. d. Math. Wiss. Gomin. 

 Leiden Suppl. 23. 



