SURFACE TENSION 163 



tend to become smaller, if left on the pipe, because the surface 

 contracts and drives out the contained air. 



The attraction between the molecules of one body is called 

 cohesion; that between the molecules of different bodies is 

 called adhesion. In order that a liquid may wet another body, 

 adhesion must be stronger than cohesion. Bugs and water 

 spiders can walk on water because the force of cohesion of the 

 water molecules is greater than the force of adhesion between 

 the water and the feet of the spiders. On the other hand, if 

 water wets an object, it produces the same effect as a very weak 

 glue; that is, stickiness. 



Warming a liquid increases the motion of the molecules and 

 thereby weakens the surface tension. Dissolved substances 

 also weaken surface tension. 



References : 



1. 1601 : 72-73. Surface Tension in Soils. 



2. 1803:113-116. Surface Tension, 

 a. 1607 : 36-37. Surface Tension. 

 6. 1801 : 99-101. Surface Tension. 



c. 1802 : 26-28. Surface Tension. 



d. 1804 : 134-135. Surface Tension. 



e. 1805 : 121-122. Surface Tension. 



/. 1806:57-61. Surface Tension. Oil on Water. 



g. 1807 : 151-153. Surface Tension. 



h. 1808:110-112. Surface Tension. 



i. 1809 : 99-100. Surface Tension. 



Experiment 61. Surface Tension. 



Apparatus : Glass tumbler, mosquito netting and cardboard, 

 each 4" X 4", medicine dropper, cake pan 8" X 12", funnel. 



Materials: Alcohol, camphor, small chip of wood, soap. 



a. Fill tumbler full of water, lay the piece of mosquito 

 netting on top of the water, and the card upon the mosquito 



