172 Journal of the Mitchell Society. {Dec. 



of the molecules, fx is the absolute attraction at unit 

 distance. 



It is a common text book idea that at the critical tempera- 

 ture the kinetic energy of the molecules of a liquid (gas) 

 under the critical pressure just balances the attraction. 

 The idea rests on the diminution and final disappearance of 

 surface tension at the critical temperature, and the fact that 

 a liquid at its critical temperature may be changed to a gas 

 without the addition of external energy, i. e., by an infinitesi- 

 mal change in pressure, the heat of vaporization being zero. 

 It must then be at this point that equation 23 will hold good. 

 Putting therefore for the molecular velocity, V, its value at 



this point / (derived as usual, Re being 83,250,000) 



and for R its value cv -^-, the constant c being unknown, 

 but equal for all for all substances, we get finally, 



[24] /i = d 



T /m 



m 



s/ 



In this equation T and d denote respectively the critical 

 temperature and density, and d is the same for all substances. 

 Using the values for the critical constants as given in Table 



24 we obtain for — T the values given in Table 25. 



Now if our ideas are correct and the absolute attraction ^, 

 given in equations 22 and 24 are the same, and correctly 

 measured, we have a right to combine these equations and 

 get: 



t_ L — K 



C tf d — ty D 

 = constant = m ■}= — , or, 



fi 1 / m 



d m ty d 



iv*.-t m\k ^~d~ 



[25] — S^ = constant, 



