Measuring Surface- Tension and Angles of Contact. 147 

 Mercury. 



1 



r. 



E. 



h. 



T. 



•382 



•822 



•073 



400 



•215 



•316 



•189 



398-2 



*156 



•214 



•279 



398 



•056 



•074 



•808 



398-6 



The values found for the surface-tensions of glycerine and 

 turpentine were: — 



Glycerine 65*1 



Turpentine 27"2 



All the above readings were taken at a temperature of 

 approximately 16°. The glass vessel and tubes were cleaned 

 with concentrated sulphuric acid, caustic potash, and alcohol, 

 being washed between each two in running water, and finally 

 dried and immersed in the liquid to be used. 



To apply the method to finding angles of contact it is only 

 necessary to remark that, either from an approximate solution 

 of the equation to the capillary surface (see Ferguson, PhiL 

 Mag. July 1914) or by assuming the meniscus to be spherical 

 in the limit, it follows that lim r/R = cos 0, where 6 is the 



r^O 



angle of contact. Thus if we plot values of r as abscissae 

 and values of R as ordinates, we get a curve the inclination of 

 the tangent to which at the origin is tan -1 (cos#). If the 

 tangent makes an angle of 45° with the axis of x, the value 

 of 6 is 0° and the liquid may be truly said to wet the tube. 



The following tables give readings of r and R for glycerine 

 and turpentine respectively : — 



Turpentine. 



Glycerine. 



T. 



E. 





r. 



E. 



•385 



•674 



•385 



•549 



•247 



•341 





•247 



•284 



•162 



•178 





•154 



•16 



•128 



•137 





•09 



•093 



•09 



•093 





•038 



•038 2 



•038 



•038 









