130 



CAPILLARITY. 



235. Capillary Attraction. The statements 

 made concerning the equilibrium of liquids are subject to 

 one important modification. When the vertical sides of 

 the containing vessel are very near each other, as in the 

 case of small tubes, the force of adhesion manifests itself 

 in a way known as capillary attraction. 



236. Capillary Phenomena. If a clean glass 

 rod be placed vertically in water, the water will rise above 

 its level at the sides of the glass. If the rod be now 

 plunged into mercury, this liquid will be depressed instead 

 of raised. If the experiments be repeated, it may be noticed 

 that the water wets the glass while the mercury does not. 

 If the glass be smeared with grease and placed in water, 

 the surface of the water will be depressed ; if a clean lead 

 or zinc plate be placed in the mercury the surface of the 



FIG. 78. 



mercury will be raised. In this case the greased glass will 

 come out dry, no water adhering to it, while mercury will 

 adhere to the lead or zinc. This is found to be invariably 

 true: all liquids that will wet the sides of solids 

 placed in them will be lifted, while those that do 

 not will be pushed down. In the figure, a represents 



