THEORETICAL AND CRITICAL VOLUME 23 



The values in question are therefore moderately constant, 

 averaging 22, but differ considerably from the expected 

 | R, as e.g. oxygen at o and i atm. gives 



- -- - . 



T 273x0-00143 



3 I 22 I 



Instead of ~ = we find --=--, i.e. the theoretical 



8 2-7 ^82 3.7 



number divided by about \/2. 



This rule in the first place an empirical one due to 

 Young and Thomas, may be expressed in another way. 

 The relation 



P k V k _ J^ 

 T k ' ' 3'7 



states that the critical volume is times that calculated 



3-7 



from the usual equation to a gas, or that the critical density 

 Bk is 3- 7 times the theoretical density. 



At the same time a third condition for the characteristic 

 equation is thus arrived at, and at least a point of depar- 

 ture for judging of the molecular weight in the critical 

 condition. Let us apply the result to gases. 



Thus to determine the molecular weight of carbon tetra- 

 chloride and acetic acid in the critical state we have : 



CC1 4 .... 0-556 44-9 273 + 283 



C 2 H 4 2 . . . 0-407 57-1 273 + 322 



