Critical Phenomena of Ether. 807 



appearance (v. Section E). The substance beneath the 

 disappearing meniscus quickly became densely opalescent ; 

 the top of the opalescent column slowly became less defined, 

 and the substance above it also grew opalescent till the 

 opalescence was uniform. The higher the temperature was 

 the more rapidly did the meniscus fade and the less marked 

 were the opalescent phenomena. In each case the final 

 appearance was that produced by slowly cooling the tube as 

 in 1 (a) to the same temperature. The height at which the 

 meniscus faded varied considerably with the rapidity with 

 which the temperature was raised to the desired temperature. 

 The more rapidly the temperature was raised the greater was 

 this height, which might be as much as 3' 5 cm. above the 

 plunger. 



(5) If the temperature was quickly raised as in (4) and 

 was then allowed to fall steadily before the liquid phase bad 

 become opalescent, an opalescent zone gradually appeared at 

 the level at which the meniscus was fading and became denser 

 as 0c was approached, till at length a meniscus appeared within 

 the zone and the opalescence then faded away. The pheno- 

 mena were practically a rapid repetition of those described 

 in 1 (a) (b) and (c), confined, however, to a very short length 

 of tube. The more promptly these operations were carried 

 out, the shallower and more definite was the zone, the upper 

 and lower limits of which sometimes had almost the sharpness 

 of a meniscus. 



In tubes VII. and XIII. the equilibrium phenomena were 

 similar to those of tube XIV. except that in tube XIII. the 

 meniscus was higher, the more nearly the temperature 

 approximated to 6 C . The variations in the transitory pheno- 

 mena are dealt with in later sections. 



D. Influence of Gravity. 



The tube described in Section A was designed for the 

 purpose of testing the extent to which the abnormal com- 

 pressibility at the critical volume predicted by Gouy from 

 Clausius's equation accounted for the observed phenomena. 

 The intention was to raise the bell to such a height that the 

 meniscus disappeared within it, giving place to a zone of 

 transition. The bell would then be gently lowered, carrying 

 with it the transition zone. In this way the pressure at that 

 zone would be increased by the hydrostatic pressure of the 

 column of ether through which it was lowered, and theoreti- 

 cally the zone should then rise in the bell. 



It was essential that the last traces of permanent gas 



