Laws of Molecular Force. 237 



In the first place, we see from what has gone before that 

 the same law cannot apply to both elements and compounds, 

 nor can the alcohols and water follow the same law as regular 

 compounds. 



In the case of the elements and methane we have the critical 

 volume, pressure, and temperature given in terms of R, Z, and 

 k by three relations (see end of Section 2), 



_QZ./0 _11 T- 16 l 



Whence, in the supracritical equation replacing R, /, and k by 

 their values in terms of v c , p c , T c , we get 



which shows that when the critical values are made the units 

 in the measurements of the variables, one and the same law 

 holds for the elements above the critical volume. 

 Below the critical volume we have 



p.v, 16 T. v j3 



We have seen that b is nearly the same for these bodies and 

 that /3/v c is approximately constant, so that below the critical 

 volume the elements and methane all follow approximately 

 the same law. 



In the case of compounds, we have (see Section 4, at the 

 beginning) 



-ma -Hi t- 120 ! 

 ».-'*/<>> Po- 4 o9£2> ^~409RF 



with which, eliminating R, k, and I from the supracritical 

 equation, we get 



^_20T/ 2 \ 409 1_ 



A~* TA i + 7 !L + 1> ) 42 7 L+1 ' 



pv 



6 v ' 6« 



Hence, above the critical volume the compounds follow the 

 same law among themselves. 



In the same way, below the critical volume we get for 

 compounds: — 



