MAGNITUDE OF THE COHESIVE FORCE OF WATER 239 



J 



t 



L 



m 



Fig. 65. Apparatus for demonstrating the development of tension in a ^vater column 

 as a result of evaporation. {A) beaker of boiled water, (B) glass tube, (C) porous 

 clay cup filled with water, (D) capillary glass tube filled with water, (£) mercury 

 layer in bottle. For successful operation it is essential that the water in (C) and 

 (D) be free of air bubbles. This is accomplished by boiling the water in (A) and 

 allowing the hot water to siphon through the apparatus and out at (B). To perform 

 the demonstration the beaker {J) is removed from around the porous cup (C). 



