Attraction of Mass, and some New Gas Equations. 93 



It will be seen (Table IV. ) that x is indeed constant 

 for substances widely different in chemical and physical 

 properties. 



The values of p c and v c have been borrowed from ( Phy- 

 sikalische Tabellen/ Landolt-Bornstein, Berlin, pp. 181-186 ; 

 those marked (*) from ' Handbuch der Physik,' A. Winkel- 

 mann, vol. iii. Leipzig, 1906, pp. 859-868. As small changes 

 of p c cause large changes of v c> care has been taken to select 

 corresponding values of p c and v c , as will be noticed. 



Adopting as the mean value of x, 



x — 3 . 10~ 6 P , or about 3 dynes, . . (45)^ 



we find for the critical pressure p G or the critical Inward 

 Pressure p lc , 



^ = ^ = iS- 3 - 10 " 6 ' if p » =1; • • < 46 ) 



and for the critical volume, 



CM 2 Ol 



and the values thus calculated for p c and v c appear to be well 

 within the margin of observational error. 



The equations deduced in Section II. afford some more 

 relations that are of interest. 



Substituting 2p c ■ v c = 1 (v. eq. 20), we find for equa- 

 tion (44) 



*=3.10-«= 2^ 2 (48) 



The table shows also in this case great constancy. 



We now possess "two independent methods of fixing the 

 value of c , the constant of molecular attraction at 0°, v = l, 

 and 760 mm. 



According to equation (17) we have for gases with 

 T c >273, 



C — 2 Vc > 



whereas equation (40) gave 

 hence 



c = -± .3.10" 6 (x- 3.10" 6 ) 

 4 



M 2 

 c =± Vc =»± 3.10- 6 (49> 



