16 



THE TKUE VALUE OF a OF TAN DER WAALS' 



of Lj{L — E) close to, or but a short distance from, the critical 

 temperature, for 25 substances of Young's of very different kinds. 

 1 have not been able to compute it close to the critical temperature 

 in all cases, but as a rule it has been calculated at from 5° to 10° 

 from the critical. In some cases I have been unable to find data 

 close to the critical and have had to compute the ratio 20 — 60° 

 below the critical. The value of the ratio does not vary more than 

 one or two per cent for a considerable distance, 40°- — -50°, below 

 the critical. At low temperatures, however, the value of the ratio 

 will be lower than close to the critical. One cannot usually employ 

 the values closer than 3° — 5° of the critical, for the reason that 

 the pressure as computed by Biot's formula is slightly high close 

 to the critical temperature, as Mills has shown. The result will 

 be that the ratio will be too high close to the critical temperature, 

 as L — E will be too low. To show the general trend of the 

 ratio of L\{L — E) I have computed methyl acetate, SnCl A and 

 benzene for several temperatures. There is a slow advance in the 

 constant as is to be expected up to the critical temperature. 





Methyl 



acetate 





t 



L 



L — E 



L/(L- 



100 



88.39 





1.114 



200 



50.56 





' 1.152 



220 



34.87 





1.157 



230 



20.99 





1.159 



233 



11.70 





1 .163 



233.7 













Benzene 





80 



95 .45 



86.70 



1.101 



140 



S2.82 



73.4 



1. 128 



220 



62.24 



53.8 



1 .157 



200 



43.82 



37.56 



1.166 



280 



27.43 



23.45 



1.170 



288.5 















SnCl A 





100 



31.76 



29.1 



1 .092 



200 



24.57 



21.59 



1.138 



240 



20 . 8-6 



IS. 15 



1 .149 



260 



18.50 



16.02 



1. 155 



280 



15.60 



13.45 



1.160 



318.7 













E) 



