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Date. 



EXERCISE 7 



True Specific Gravity 

 Purpose. — To determine the real specific gravity of any sample of soil. 



1. Fill a specific gravity bottle with distilled water and weigh it (Fig. 7). 

 Pour out part of it and add ten grams of oven-dry soil. Heat the content 



■iiiiiiiiii^^ 



Fia. 7. — An accurate scale with agate bearing is a valuable part of 



L'ciuipment for studying agricultural 



slightly to drive out any air adhering to the soil. Now refill the bottle 

 with distilled water and weigh again. 

 2. Divide the loss in weight of water into the weight of soil to find the specific 

 gravity. Record the results in the following table. 



Specific Gravity of Soil Grains 



Wt. bottle and waten Soil, bottle water Water displaced Specific gravity 



Note. — Students should, if possible, compare the real specific gravity of sand, clay, 

 humus soil and others. 



QUESTIONS 



1. What precaution should you take in the careful performance of this 



exercise? 



2. Why are specific gravity bottles provided with glass stoppers having small 



openings? 



