LABORATORY PRACTICE 229 



should be put together, the filter paper and cheese-cloth 

 carefully tied in place, and the lower three sections filled 

 with sand and settled, adding enough sand so that the 

 settled sand shall stand slightly above the joint between 

 sections 3 and 4 from the bottom. Then the fourth section 

 should be filled with the gravel or coarse sand. After this, 

 the remaining sections which have been properly put 

 together should be screwed on to section 4 from bottom, 

 first being careful to clean and vaseline the upper threads 

 of section 4. 



EXPERIMENT 5 

 Surface Tension 



(A) The materials needed for this experiment are : 



1. A small dish of fine sand. 



2. A shallow dish or watch glass. 



3. A beaker of water. 



4. A heated clean iron surface. 



(B) To perform the experiment : 



1. Place a small quantity of water in the dish or watch 

 glass. 



2. Slowly pour fine sand into the water in the dish 

 until more sand has been poured in than the water will 

 moisten. 



3. After thirty seconds invert the dish to permit the 

 unmoistened portion of the sand to fall away. 



Observe : The dish may be held in any position and 

 the moistened sand will not fall away from it. Why ? 



4. Set the dish in position and with a sharpened pencil 

 or rod break the sand into small masses of various sizes. 

 It will be found that masses of considerable size may be 

 lifted upon the point of the pencil or rod without breaking. 



