132 Mr. W. Sutherland on t he 



at points remote from that the agreement is good : thus, at 

 volume '002053 Amagat's experimental pressure is 320 metres 

 of mercury, while the equation gives 338. The difference 

 between the two results is seen to be negligible if we look at 

 it in another light. Thus, for a pressure of 320 metres of 

 mercury the equation gives a volume '002073, which differs by 

 only 1 per cent, from Amagat's measurement for the same 

 pressure — a difference quite within the present limits of expe- 

 rimental error in the measurement of small volumes at high 

 pressures. 



Let us now proceed to the important question of the true 

 critical temperature of C0 2 . The critical temperature, volume, 

 and pressure are determined by the characteristic equation, 

 and the two equations 



|P = and |^=0, 



v do 



which may be written 



aT -\ cT-Z 

 F= _-^T. + __ (1) 



«T/\ , h x -^ „cT-Z 



4b 

 v VT 

 Eliminating the exponential factor from (2) and (3), we get 



Considering that \X must be taken with a positive sign, 

 only the positive root of this equation for — -= is permissible, 

 and we have at the critical state 



VT 2 J J 



and eliminating v between this and (2) we get 



0=-«J/l+ * V"*-*^, ... (2) 



0^( 2 + 4_ + ^)^ +6 ^. . . (3) 

 v \ v v 7 T v*l/ it v 7 



oT — 7 



... =2/f +«VT(l+/K-2/i, 



