Critical Phenomena of Ether. 821 



density of filling was only 0*285 (density of ether at 0° C. 

 being taken as 07362). If, however, sufficient traces of per- 

 manent gas or other impurities were present the task would 

 be simple — it is quite probable that in tube XIII. the reluc- 

 tance of the meniscus to ascend to the top was due to the 

 trace of permanent gas known from the tests of Section A to 

 be present — but in this case the results would no longer 

 necessarily apply to the pure substance. 



The slight difference in C for the tubes XIII. and XIV. 

 is not to be taken as Lending support to Battelli's results. 

 The values given in Table 1. are for the appearance of the 

 meniscus with fall of temperature. If the ordinates, or lines 

 of constant volume, are traced on Andrews's diagram for 

 various values of v in the neighbourhood of V c , it becomes 

 evident that since the separation into two phases can only 

 occur when the given ordinate reaches the saturation curve, 

 the meniscus should appear at temperatures varying with the 

 specific volume and diminishing as the specific volume differs 

 more from V c . Since in tubes XIII. and XIV. the meniscus 

 appeared invariably at the upper and lower extremities of the 

 respective tubes, V c evidently lay between the two specific 

 volumes, and if it lay nearer to the specific volume of tube XIV. 

 the slight difference of temperature might be predicted from 

 Andrews's theory. It was difficult to determine the exact 

 temperature of disappearance on raising the temperature, 

 partly because of the gradual nature of the change, partly 

 because of the opalescent effects which rendered observation 

 difficult, but in general the temperature of disappearance in 

 both tubes seemed slightly higher than that of appearance, 

 and was certainly not lower for tube XIII. than for 

 tube XIV. 



Other observers, like Battelli, have observed remarkable 

 differences of density at C or slightly above. Since the differ- 

 ence in the mean densities of tubes XIII. and XLV. is about 

 11 per cent, and the menisci disappeared practically at the 

 top and bottom of the respective tubes (given a sufficiently 

 gradual rise in temperature), it follows that at the tempera- 

 ture of disappearance the difference of density could not 

 have exceeded that amount. 



Mathias (19) shows, however, in his analysis of the liquido- 

 genic theories that it is quite possible to frame a theory 

 which will coincide with the classical theory of Andrews in 

 its predictions concerning the final states of equilibrium, 

 whilst it will also account for the transitory differences of 

 density which have been held to show the insufficiency of 

 that theory. It is the theory according to which the ratios 



