Measuring the Surf ace-Tension of Liquids. 



397 



edge seemed to enter the liquid at once when lowered, and 

 when raised slowly parted from the liquid first at the two 

 ends and lastly in the middle of the lower edge. After 

 adjustment the holder and plate were washed, dried over a 

 Bunsen flame, attached to the balance in the same way as 

 the frame (fig. 2), left hanging over the liquid to be examined 

 until the temperatures were nearly the same, then weighed. 

 The index of the balance was next set exactly at zero, taking 

 care that the beam was not lifted, and the liquid slowly raised 

 by turning the screw-handle s until it touched the plate. The 

 weight was again adjusted to bring the index exactly to zero. 

 For a second determination the plate was lifted out of the 

 liquid by tipping the balance-beam, the liquid lowered a little, 

 and after all visible disturbance of the surface had ceased the 

 operation of setting was repeated. The surface-area of the 

 liquid must be so great that the measurement is not sensibly 

 increased by the lowering of level due to the capillary 

 elevation; or else this must be taken account of in the 

 calculation. 



It was necessary to ascertain, in the first place, whether the 

 contact-angle can be considered zero to the limit of accuracy 

 attainable by this method, and if so under what conditions. 

 I proceeded to try plates of various materials in some liquids 

 whose tension could be found by Michelson's method. 



(1) Glass Plate in glycerine. 



A microscope cover-glass, 5*044 centim. long and '026 

 centim. thick, was cleaned, dried, and touched to the glycerine 

 surface without being allowed to sink even momentarily 

 deeper. The first three weighings were made rapidly ; the 

 last three after an hour's contact. 





w (gram). 



Tcos0 

 (dynes). 



Temp. C. 



1. 



2. 

 3. 

 4. 

 5. 

 6. 



•6405 

 •6391 

 •6420 

 •6550 

 •6536 

 •6534 



61-92 

 61-79 

 6206 

 63-32 

 63-07 

 63-12 



o 



166 



;> 



169 



The tension, as found by Michelson's method immediately 

 afterwards, was 



63-14 dynes at 17° C. 



