Density of Liquids and Refractive Index of Liquids. 451 



while the corrected readings fit the curve almost perfectly, 

 the uncorrected readings corresponding to curve A differ 

 from the theoretical values by amounts which vary greatly, 

 especially for the first fifteen seconds. The curves A and B 

 diverge in the position corresponding to the time when the 

 observations ended ; this is perfectly consistent with the 

 theory, though the curves would of course meet ultimately 

 at t = co . 



Physical Laboratory, 



The University of Sheffield, 



May 29, 1912. 



XLI. Density of Liquids and Refractive Index of Liquids in 

 Contact. By A. L. Clark, Ph.D., Prof, of Physics, Queen's 

 University, Kingston, Ontario *. 



WHILE experimenting with various pairs of liquids which 

 remain sufficiently insoluble to maintain a meniscus 

 of separation, I came across the phenomenon described below. 

 Chloroform, which is nearly insoluble in water and possesses 

 a density of about 1*4 at ordinary temperature, has a 

 critical density of about *5. The density of water at 260°, 

 the critical temperature of chloroform, is about '66, so that as 

 the temperature rises, the density of chloroform falls oft 

 more rapidly than that of water, and at one temperature 

 they are equal. I placed chloroform and water together in a 

 Natterer's tube and heated in a paraffin bath. At a few 

 degrees below the critical temperature of chloroform the 

 equilibrium becomes unstable and the system overturns, 

 the chloroform rising to the top. As it cools down again 

 the chloroform sinks again to the bottom t. 



The temperature at which the phenomenon occurs is 

 higher than was expected from the study of liquid density 

 curves of other liquids (that for chloroform seems never to 

 have been investigated). This is due no doubt to the solution 

 of chloroform in the water and water in the chloroform 

 tending to equalize the densities. With pure chloroform and 

 water, however, the upset is certain. The phenomenon is 

 very interesting to watch, particularly when the system is 

 cooled. The chloroform settles down into the water stretching 

 the surface film more and more, and finally breaks through. 



Another very interesting phenomenon discovered in the 



* Communicated by the Author. 



t The same phenomena may be seen with aniline and water. 



