and the Properties of Liquids. 585 



obtained from the preceding expressions very nearly obey this 

 law. Thus the values of the intrinsic pressures in atmo- 

 spheres for ether at the temperatures 273° and 373°, given by 

 the expression L^, are 2664 and 1546, while the value at the 

 critical point is 235'8. The ratio of these values to the 

 corresponding values of p* are 4916, 4148, and 3472, 

 respectively, and thus approximately constant. Thus although 

 matter consists of molecules, a liquid behaves approximately 

 as if the matter were evenly distributed in space, and the 

 attraction independent of the temperature. 



Since the density of a liquid at the absolute zero is about 

 4 times that at the critical temperature, the intrinsic pressure 

 in the former case. is about 16 times that in the latter. 



It is of interest that the intrinsic pressure term in Van der 

 Waals' equation of state is of the same form as the above, and 

 thus corresponds to an even distribution of matter in space. 



A better agreement of the above expression with the facts 

 is obtained by writing p 2 ' 33 instead of p 2 . Since the intrinsic 

 pressure is for all liquids at corresponding states the same 

 multiple of the critical pressures, its general equation must 

 take the form 



••=<) 



The value of A when V n is expressed in atmospheres is 

 6-52. 



Since L^WKp! in the case of a liquid, we have 

 L 2 = WKp 2 in the case of its saturated vapour, and therefore 



From Clapeyron's equation we have 



Pt 



and hence 



L .-M T »-)(H> 



since the ratio j~ from these equations is the same as that 



2 



given by the above equation. These equations must hold if 



matter is evenly distributed in space ; from what has gone 

 before we would expect them to agree approximately with 

 the facts. 



They afford a test sometimes whether matter is evenly 

 distributed in space. For example, the values of p 2 and p 

 for the vapour of water at zero are the same as for the 



