LABORATORY PRACTICE 231 



EXPERIMENT 7 



Surface Tension 



(A) 1. Introduce a small amount of water (one or two 

 grams) into a watch glass or other shallow dish. 



2. Pour sand steadily, and in a small stream at one 

 point, into the water until the water is completely taken 

 up by sand. Pour in an excess of dry sand. The sand 

 mass will be found to take a form similar to that shown 

 in Fig. 18 of the text. 



3. After 15 seconds, the dish should be slowly inverted 

 to permit the dry sand to fall away from the surface of 

 the mass in the dish. 



4. The dish may now be held in any position and the 

 pyramid of moist sand will usually not break. Why ? 



5. Draw a diagram or sketch to show the manner in 

 which, as you understand it, the pyramid is kept in posi- 

 tion. 



(B) 1. Place the dish in position on a stand or table. 



2. Pour a very small amount of water down the inner 

 surface of the dish. The pyramid of moist sand will 

 collapse. Why ? 



EXPERIMENT 8 



Specific Heat of Wet and Dry Soils 



Where the apparatus is available, determine the specific 

 heat of wet and dry soils, using Hosier and Gustafson's 

 method as described on page 40 of their Soil Physics 

 Laboratory Manual, or McCall's, as described in his 

 Physical Properties of Soil, p. 74. 



