Measuring the Surf ace-Tension of Liquids. 



(5) Platinum in distilled water, 



Plate the same as in (2), dipped 1 millim. 



399 



w. 



T cos e. 



Temp. C. 



•9536 

 •9544 



73-26 

 7332 



15-28 

 1510 



The mean of these corresponds to 73*31 dynes at 15°*04, at 

 which the tension was found by a frame to be 73*36 dynes. 

 Another trial with water freshly boiled gave with the plate 



Tcos0 = 72-10, 

 and with a frame 



T = 72-76, 

 both at 19°-9 C. 



In all these cases the platinum plate was washed with a 

 caustic soda solution, well rinsed either in distilled water or 

 at the tap, and made red-hot in a Bimsen flame before touching 

 the liquid. 1 found that if the plate touched the liquid surface 

 before it had time to cool after leaving the flame, the contact- 

 angle would remain (sensibly) zero for a few minutes, without 

 dipping the plate at' all. It seems probable that condensation 

 of air upon the plate may be one cause of the failure to get a 

 zero angle. When the plate was washed without alkali, 

 with or without acids, I failed to make the contact-angle 

 even approximate to zero. 



(6) Platinum in a dilute solution of caustic soda. 

 Plate the same as in (2). 



w. 



T cos e. 



Temp. C. 



•9023 

 •9019 

 •9019 

 •9019 



69-32 

 69-29 

 69-29 

 69-29 



1624 

 16-24 

 1622 

 16-20 



By a frame, T^ 69*36 dynes at 16°*17. 



(7) Silver plate in distilled water. 



This plate was 7*625 centim. long, -0025 centim. thick. 

 It was washed in caustic soda solution, then in water, and 

 dipped 1 millim. into the liquid before each weighing. 



