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PRACTICE 11 



Determination of Real Specific Gravity of Soils. Picnometer 

 Method. 



Use sand, loam, silt, clay and peat. 



Fill a picnometer to the end of the capillary tube with distilled 

 water whose temperature is known. Wipe dry and weigh. Pour out 

 about half of the water and add about ten grams of soil (about half 

 as much peat) that has been carefully weighed. It is a good plan to 

 weigh the flask just before the soil is added and again just after, the 

 difference being the weight of the soil. In this case the soil need not 

 be previously weighed. 



Boil gently for a few minutes in the water bath, sand bath or on 

 an asbestos mat to drive out the air from the soil. Refill with dis- 

 tilled water, bring to the same temperature as before and weigh. 

 Determine the amount of water-free soil, using the percent of hygro- 

 scopic moisture found in Practice 6. The weight of the flask of water 

 plus the weight of the soil, minus the weight of the flask containing 

 the soil gives the weight of water displaced by the soil. Calculate 

 the specific gravity and tabulate results. 



Compare the real specific gravity with the apparent specific gravity. 



Why is the real specific gravity higher? 



