Grade. 

 Date. . 



(42) 



EXERCISE 15 



Hygroscopic Moisture 

 Purpose. — To doterminc tlic percentage of hygroscopic moisture in air dry 



nh: 



PLAN 



Number and weigh five evaporating dishes. 



Into the above dishes weigh 25 grams of each of the five soils remaining 

 from tlie exercise for the determination of the capillary moisture. 



Fig. 8. — Drying oven with top tubes for thernu 

 eter and gas regulator. 



l^_^ 



Fig. 9. — Moisture-proof 

 chamber for use in cooling 

 oven-dried samples before 

 weighing. IMoisture-ab- 

 sorbing chemicals, as strong 

 sulfuric acid, may be 

 placed in the lower part to 

 insure dryness. 



3. Dry these samples in an oven (Fig. 8) vrliich has a temperature slightly 



above the boiling point of water. 



4. Later cover the dishes and remove from the oven and allow to cool in a 



dry chamber (Fig. 9). 



5. Weigh rapidly and determine the loss of moisture. 



6. Determine the per cent of hj'groscopic moisture by dividing the weight 



of moisture lost by the weight of oven dry soil. 

 If possible the degree of humidity of the air in the room should be found on 

 the day this exercise is conducted. If desired this exercise may be 

 repeated on very dry and very wet days to determine the variation in 

 amount of hygroscopic moisture. 



