PRACTICE XIII 



DETERMINATION OF REAL SPECIFIC GRAVITY OF SOILS 



Each student will use a light and dark soil provided by the 

 instructor. 



First determine the hygroscopic moisture as in Practice VI 

 and tabulate on opposite page. Fill a 50-cc. pycnometer to the 

 top of capillary tube in glass stopper with freshly boiled and 

 cooled distilled water whose temperature is known. Wipe pyc- 

 nometer dry and weigh. Pour out about half of the water and 

 weigh. Add about 5 g. of soil (about half as much in case of 

 peat) and weigh again ; the difference is the soil added. In this 

 case the soil need not be weighed accurately beforehand. 



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

 on an asbestos mat to drive out the air from the soil. Refill 

 with distilled water, bring to the same temperature as before, 

 and weigh. From the per cent of hygroscopic water as deter- 

 mined calculate the weight of water-free soil used. 



The weight of the pycnometer full of water plus the weight of 

 water-free soil added, minus the weight of the full pycnometer 

 containing the soil gives the weight of water displaced by the 



i rr^i weight of water-free soil 

 soil. 1 hen -P- = specific gravity, 



weight 01 water displaced 



Compare real with apparent specific gravity. 

 Why is the real specific gravity higher ? 



REFERENCES. 



" Soils," Lyon and Fippin, pp. 94-96. 



" The Soil," Hall, p. 63. 



"Physical Properties of Soils," Warington, pp. 41-42. 



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