Critical Phenomena of Ether. 795 



Elaborate precautions were taken to secure the purity of 

 the ether, and especially to free it from the last traces of 

 permanent gas. The submersed bell described in Section A 

 proved a delicate means of detecting the slightest traces of 

 gaseous impurity, and showed the precautions taken to be 

 quite necessary for the attainment of the best results. It 

 was possible thereby not only to test the efficiency of the 

 means adopted for purifying the ether, but also to classify 

 the tubes prepared according to the relative amounts of 

 impurity contained. The observations made with these 

 tubes proved that extremely slight traces of gaseous impurity 

 might visibly modify the critical phenomena. 



By means of the bell above mentioned the part played by 

 hydrostatic pressure in the Cagniard-Latour phenomena was 

 tested, and found to be probably negligible. 



The effect produced by Yillard with ethylene was repro- 

 duced in the tubes of ether, and the density difference so 

 produced was carefully compared with that associated with 

 the Cagniard-Latour phenomena in the pure substance. The 

 conclusion arrived at was that these were essentially 

 identical. 



The opalescent phenomena were carefully examined, and 

 explanations are suggested of some of the peculiar opalescent 

 effects described by earlier investigators. Some account is 

 also given of preliminary observations which were made 

 with a view to determining the nature of the opalescent 

 particles. 



The investigation has led to the general conclusion that 

 the phenomena observed in the pure substance may readily 

 be explained in accordance with the theory of Andrews, 

 whilst the phenomena, both qualitative and quantitative, 

 which have been advanced as demonstrating most strongly 

 the insufficiency of that theory are to be observed only in 

 tubes which contain distinct traces of impurity. 



Before proceeding to the experimental work, I would like 

 to point out that if the differences of density can be 

 adequately accounted for, the various other phenomena 

 which have been held to invalidate the Classical Theory 

 need present no difficulty. Cailletet and Collar deau (4) 

 have shown that iodine dissolved in liquid C0 2 remains in 

 solution in the denser substance above 6 C , although the less 

 dense substance does not acquire the property of dissolving- 

 iodine. Hagenbach (5) found that the resistance of a very 

 dilute solution of sodium iodide or bromide in sulphur 

 dioxide remained less in the upper portion of the tube than 



3 G2 



