16 Mr. W. Sutherland on the 



We found that p c would have to be constant for the whole 

 family, as the last table shows that it nearly is for A, Kr, 

 and X at about 50 atmos. But p c for He is about 2*5 atmos. 

 It looks as if the assumption that critical volume is propor- 

 tional to limiting volume and also to T c / p c cannot be extended 

 to the extreme case of He in this family. The ratio of B 

 to 10- 6 (M 2 Z)5 in this family is constant, namely 4-0/0-4 = 10, 

 the same ratio for ordinary atoms in compounds having a 

 value about 10, and for the element gases H 2 , 2 , and N 2 a 

 value about 20. In this family then we have s = /ca 3 , as in 

 the other chief non-metals. The atomic weights of these 

 elements will be taken to be those given by their densities, 

 namely, He 3*968, Ne 19'96, A 39'96, Kr 83% and X 131, 

 though they could equally well be taken at the nearest whole 

 number. 



In the families of oxygen and nitrogen B can be obtained 

 for all but the first member of each from the density of the 

 solid element, with a small amount of uncertainty on account 

 of different allotropic forms. For oxygen the kinetic theory 

 gives B = 6'16, and for nitrogen 8'00. When we pass to the 

 carbon family we find that allotropy causes considerable uncer- 

 tainty in the case of carbon itself, for B==3'6 in the diamond, 

 and 5'58 in graphite, and about 8 in the compounds of carbon. 

 I shall take the smallest of these as the one to be used in 

 testing (8). The data and derived quantities are collected in 

 the following table leading to the values of (N' — 1) Vp 1 / 3 / 

 KB 2 % 2/3 in the last row, which by (8) is to be constant. It 

 is to be remembered that K is got from N' — 1 and B by the 

 relations (N'-1)V=(N-1)B and K=N 2 . 









Table V. 











He. 



Ne. 



A. 



Kr. 



X. 



u 





** 



1 



2 



3 



4 



{W 



-l)t 



0-8074 



1-537 



6369 



9-532 



15-45 



B 





4 



8 



12 



16 



20 



N 





1-202 



1192 



1-531 



1-597 



1-773 



K 





1-444 



1-421 



2-344 



2551 



3-144 



P 





0-992 

 •3511 



2-496 

 •3667 



3-331 



•4877 



5-200 

 •4903 



6-551 





•495. 









R 



CI. 



Br. 



I. 





u 





1 

 2-153 



2 

 8-614 



3 

 12-62 



4 





(N'-1)V . 





21-53 





B 





6-6 



13-2 



19-8 



26-4 





N 





1-326 



1-652 



1-637 



1-816 





K 





1-758 



2-729 



2-679 



3-298 





n 





2-879 

 •4953 



2-681 

 •4946 



4-040 

 •4926 



4-810 





r 





•4933 



