230 APPENDIX 



Why ? Draw a sketch to illustrate your idea of how the 

 particles of sand are held together. (See Fig. 17.) 



5. Place one of the masses of wet sand upon the hot 

 iron surface and note its behavior. After a few seconds 

 the mass begins to collapse. Sometimes it collapses a 

 part at a time. Sometimes the whole mass suddenly 

 collapses. In either case the grains of sand fall apart and 

 scatter about over the heated surface. Why? 



6. Lift a mass of the wet sand upon the point of a 

 pencil and carefully bring it over a vessel full of water ; 

 then slowly and carefully lower the mass till some point of 

 it comes just in contact with the surface of the water, and 

 note what happens. Suddenly a portion of the mass, or 

 possibly all of the mass, breaks away from the point of the 

 pencil and settles to the bottom of the glass, but it will 

 be observed that within the body of water the grains 

 of sand become independent of each other and spread apart 

 as they settle. 



Why do they break away from the pencil ? 

 Why do they spread apart as they settle ? 



EXPERIMENT 6 



Surface Tension 



The experiment (5) may be repeated using loam and fine 

 clay. If fine clay and frequently if fine loam be used, 

 the behavior of the moist mass, when placed upon the 

 hot surface, will be different from that of the mass of fine 

 sand, and will illustrate another very important action of 

 the capillary film. 



