Section III., 1915 [43] Trans. R.S.C. 



Viscosity of Ethyl Ether near the Critical Temperature. 

 By A. L. Clark, B.Sc, Ph.D., F.R.S.C. 



(Read May Meeting, 1915). 



The problem of the critical point has been discussed for a number of 

 years, but cannot be said to have been settled definitely. The problem 

 may be put thus: Is the critical temperature the true upper limit of 

 temperature for which a substance may exist in the liquid state, or does 

 the liquid state persist above this temperature, even though the sub- 

 stance appears to be perfectly homogeneous. The classical definition of 

 Andrews as the temperature above which the liquid may not exist, or the 

 upper limit of the liquid state, has seemed insufficient to many experi- 

 menters. The following experiments^ may be cited as some of those 

 which have given rise to the objections to the classical theory. 



While according to Andrews' theory there is only one volume of 

 filling of a tube, viz., the critical volume, that should allow the meniscus 

 to be observed as it disappears at the critical temperature, it was 

 found by Cagniard de la Tour that there was considerable latitude 

 to the initial volume of liquid in the tube for the meniscus to disappear 

 in the body of the tube. Galitzine^ found that with ethyl ether 

 these limits were • 28 and • 48 of the volume of the tube, while the critical 

 volume is approximately half way between them. It has been pointed 

 out that the temperature of the disappearance of the meniscus is not 

 identical with the true critical temperature as defined by Andrews 

 and as shown by the point where the isothermal has a horizontal 

 inflexional tangent. Then, too, it has been found that differences 

 in density in different parts of the tube persist after the meniscus has 

 disappeared. It has also been shown that after heating above the 

 critical temperature and cooHng again, the position of the meniscus 

 depends on the amount and duration of the heating above the critical 

 temperature. Finally, if two non-miscible liquids are placed in an 

 0-shaped tube and the tube is heated above the critical temperature 

 the manometric heavier hquid does not reach the same level in the 



1 See Mathias, Le Point Critique des Corps Pur for a very comprehensive 

 discussion of the various abnormalities observed near the critical point. Also Kuenen, 

 Die Zustandsgleichung der Case und Flussigkeiten und die Kontinuitatstheorie 

 for an account of these experiments and the objections to the conclusions drawn 

 from them. 



2 Galitzine. Wied. Ann 50, 521, 1893. 



