﻿Opalescence of Gases in the Critical State. Ill 



various ways* by aid of Maxwell's well-known condition. 

 Developing all variables in series in the neighbourhood of 

 the critical point we get the reduced specific volumes in the 

 liquid and gaseous state as functions of the absolute value 

 At of the distance from the critical temperature 



^ = 1-2 VAt+^At, 



1 Q 



<£ 2 =l-f2 \/At+~At. 



Thus the apparent critical temperature, when the meniscus 

 appears at the lower or higher end of the Natterer tube 

 according as A<£:$0, is less than the true critical temperature 



by At=~-t--, and the opalescence in this state will be 



inversely proportional to the value 



being thus slightly greater for negative than for positive 

 values of A<£. 



For higher temperatures (the one-phase state) we can 

 replace (7) approximately by 



g = -6g[AS + 2A T ],. . . . (10) 



if AS denotes the excess of the actual temperature over the 

 apparent critical temperature. But if the temperature falls 

 below the point of separation by AS we must put 



!^ = _6^T2AS + 2At1 (11) 



dv Vc L J 



Thus we see : 1. For a given temperature the opalescence 

 is smaller, if the specific volume is greater or less than the 

 critical volume (in accordance with former observations). 



2. The opalescence of the two coexisting, liquid and 

 gaseous, phases is roughly equal; by taking into account 

 higher terms it is found to be smaller for the gaseous state. 



3. The opalescence diminishes more slowly (twice a> slow 

 if A0 = O), when the temperature rises above the point of 

 separation than when it falls below it. 



The same conclusions remain substantially valid it' we 

 * See/, i. Kuenen, Zustandsglekhung (Vieweg, Braunschweig), p. 92. 



