RECTILINEAR DIAMETER 29 



data on p. 26, a corresponding departure from the rule is 

 to be expected, as is shown by the following table : 



(liquid) ^ = V t sat ' ra *0 A (5 + V 



7 T k "0! V *"*-'-' 2 ~ v 



^7 



III 



0-928 1-863 0-216 1. 1 



0-822 2-231 0.054 2 



0-733 2.457 0-015 2.1 



0-656 2.628 O-004 2-1 



0-605 2-730 I'9 



The deviation thus appears at the beginning, near the 

 critical temperature ; at low temperatures the density of 

 the vapour, which also is abnormal, is of little consequence, 

 so that the normal value 1*9 reappears. 



5. Volume at the Absolute Zero *. 



Whilst in dealing with volume relations we keep as 

 closely as possible to experimentally accessible quantities, 

 we must now consider what is the least possible volume 

 a given mass of substance can take up, i. e. the volume at 

 the absolute zero. This quantity is, of course, not completely 

 accessible to experiment, but with the means of reaching 

 low temperatures now available it ought soon to be possible 

 to arrive at the volume at the absolute zero by means of 

 a reasonable extrapolation. 



Making use, therefore, of the law of the rectilinear dia- 

 meter, we will calculate the ratio between the density at 

 the absolute zero (D ) and the critical density (D k ) by means 

 of the value at the freezing point (Z>), since for the sub- 

 stance in question the density of the vapour at that 

 temperature may be neglected. Then if t k is the critical 

 temperature in centigrade degrees we have : 



u- 

 la that way the following table is obtained : 



1 Guldberg, Chem. Centr. Bl. 1898 ; 2. 1042. 



