88 



Mr. J. Kam on Molecular Attraction and 



larger than p expansion is impossible, and the substance 

 is bound to lose this characteristic of a gas (vapour). 



Now if we heat a liquid in a closed vessel the density of 

 its vapour must increase ; its own density must decrease as 

 long as there is a difference between them and until they are 

 equal, which point is reached at the critical state. 



Consequently at the critical state the inward pressure of 

 the liquid p lL becomes equal to the inward pressure p x of the 

 gas or vapour, for both converge in opposite sense towards 

 the same value, the inward pressure of the critical fluid, and 

 the same applies to the thermic pressures pi and p g . 



Thus the critical state appears to be the limit which either 

 of the two must reach before turning into the other, and we 

 may consequently write the following equations : 



(i.e. The minimum value of the "Inward"^ 

 Pressure" p n is for a liquid equal to the 

 thermic pressure pi. ! 



e. The maximum value of the " Inward 

 Pressure " p ]g is for a gas equal to the 

 C thermic pressure p g . 

 At the critical state, however, 



Pn^Pi- 



Ph=Pa 



(27) 



thermic 



Pu = Pig* 

 Pi = Pg> 

 and it follows inevitably that at the critical state 



Pn = P^ = Pi= Pgi • • 



The " critical inward pressure " 

 substance is equal to the critical 

 pressure p c ) i.e., 



Pic = P°> 



~ttc-pi c = Pc+pi c i 



n c = 3p c = 3p lc 



The " critical Intrinsic Pressure " is 

 the critical pressure or three times 

 pressure. 



We thus arrive at the same results along an entirely 

 different line of argument. 



The exactitude of these rules, supported as they are by 

 the substantial experimental proof already recorded and by 

 that to follow presently, appears to be well established. The 

 critical state is the only state at which we can directly measure 

 the Inward Pressure. 



equal to three times 

 the critical inward 



