400 



Mr. T. Proctor Hall on New Methods of 





w. 



T cos 0. 



Temp. C. 



1. 



1-0000 



64-27 



17 ? 70 



2. 



1-0080 



64-46 



>> 



3. 



1-0035 



6449 



„ 



4. 



1-0950 



70-37 



1800 



5. 



1-0855 



69-76 



1770 



6. 



1-0850 



6973 



5J 



By a frame, T=72'84 dynes at 18°'37. 



Before the fourth weighing the plate was warmed over a 

 Bunsen flame, touched immediately to the water surface, and 

 allowed to remain in contact ten minutes. 5 and 6 were 

 taken after two hours of contact. 



(8) These results, along with some others of the same 

 kind, show that the contact-angle can be considered zero 

 for 



Glass and water, sulphuric acid, glycerine, 

 Mica and water, 

 Zinc and water, 



when the surfaces are clean, and, in the case of zinc, freshly 

 shaved ; and that the angle for 



Platinum and water, 

 Silver and water, 



can be made zero, or nearly zero, with certain precautions. 



In every case it is easy to see by a glance along the line 

 of contact in a good light whether the angle of contact is 

 zero or not. 



(9) Though there could be no reasonable doubt that the 

 angle of contact for alcohol and similar liquids would be 

 zero in nearly all cases, as some observers have supposed 

 otherwise I thought it worth while to measure the surface- 

 tension of alcohol by several different plates. If there is a 

 finite contact-angle for each plate, the values found for T cos 6 

 will be different. If these values are all alike, it is reason- 

 ably certain that the contact-angle is zero. The following 

 table gives the results. In no case was any difference found 

 in the weight after dipping the plate one or two millimetres 

 into the alcohol, provided the plate was then allowed to 

 stand two or three minutes in the normal position. During 

 the operations the surface-tension probably increased a little 

 by absorption of water-vapour from the air. 





