certain Dilute Aqueous Solutions. 371 



solution-air and the solution-glass surfaces change with the 

 concentration of the solution, so that the results obtained 

 involve two changes which cannot be separated. This renders 

 the interpretation of the results very difficult. 



Jager used a method depending on the relation between 

 the diameter of a capillary tube and the distance it must be 

 immersed in the liquid in order that the same air-pressure 

 may cause steady streams of bubbles of the same size 

 to issue from it and from another tube of known diameter, 

 immersed to a fixed depth. He determined this relation 

 empirically from experiments on water ; and he accepted the 

 results of Brunner and of Wolf as correct. 



Quincke's work on flat bubbles has been discussed in several 

 papers, and seems to be not very satisfactory. From this we 

 see that, excepting the work done by Sentis and by Klupathy, 

 the determinations of the surface-tensions of solutions are not 

 all that can be desired. 



Sentis employed an entirely different method, and one that 

 appears to be very free from objections. He draws the liquid 

 up into a capillary tube ; then removes the tube from the liquid, 

 and allows the liquid to run out so as to form a drop around the 

 end of the tube. This drop supports a liquid column of a certain 

 length in the tube. He then measures the maximum diameter 

 of the drop, focusses a microscope on the meniscus in the tube, 

 and slowly raises below the tube a beaker of the liquid. When 

 the liquid in the beaker reaches the drop, the column in the tube 

 falls ; the position of the beaker is now noted, and it is then 

 again slowly raised until the meniscus in the tube has come 

 back to its previous position, and the position of the beaker is 

 again noted. The vertical distance between these two positions 

 of the beaker is (after certain corrections are made) the height 

 the liquid will rise in a tube for which the contact-angle is 

 zero, and whose radius is equal to that of the drop. His 

 individual determinations may differ by one-half of a per 

 cent., but generally they agree very well. 



In the present work it was desired to use a method entirely 

 independent of the mutual action between the liquid and 

 a solid ; and the only methods so far devised that completely 

 satisfy this condition are Lenard's* method of vibrating falling- 

 drops, the method of Eotvosf, that employed by Sentis, and 

 the method of ripples which was first successfully used by 

 Lord Rayleigh|. Sentis's method, as described in his first 

 paper §, did not seem very satisfactory; and of the others 



* Wied. Ann. xxx. p. 209 (1887). 

 t Ibid, xxvii. p. 448 (1886). 



t Phil. Mag-. [5] xxx. p. 386 (1890) ; Theory of Sound, vol. ii. p. 344. 

 § Journ. de Phys. [2] vi. p. 571 (1887^. 



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