some other Constants of the Inactive Gases. 803 



(b) From the coefficient b of van der Waals' equation. 



As this coefficient represents approximately four times the 

 volume of the molecules, we have 



whence 



_ 3/TT 



b can be calculated from the isothermals and also from the 

 critical constants, although the values thus obtained do not, 

 as a rule, agree very well with each other. For our purpose, 

 it will be sufficient to use the ^-values obtained from the 

 critical constants. The relation is 



b = 



T, 



8-273 p k 



(p/ c being in atmos and T* in degrees absolute). 



The following table gives the values of T k , p^ b and a for 

 all the gases except neon. Those for argon, krypton, and 

 xenon were determined by Ramsay and Xravers, those for 

 helium by Kamerlingh Onnes. 





T*. 



pk. 



b. 



<7. 



Helium 



About 5° 



•2 to 3 



0-0007 



2-3x10-3 cm. ! 



Neon 



9 



9 



-i 



? 



Argon 



155° r> 



52-9 



0-001347 



2-86x10-8 cm. ! 



Krypton 



210°-5 



54-3 



0001774 



314x10-8 cm. 



Xenon 



287° -75 



57-2 



0002304 



3-42x10-8 cm. 



(c) From the dielectric constant 

 rom the relation ., 



IX 



differ much from unity, 



From the relation K — . = -r No- 3 , we get, since K does not 

 ix -p & o 



K-1 = ^N<7 3 . 



For Helium K = 1-000074 ; hence <r=l-20x 10" s cm. 



