RESEARCH METHODS IN STUDY OF FOREST ENVIRONMENT. 87 



sary to subtract 21 from the percentage of capillary moisture to 

 obtain a quantity having a fairly constant ratio to the wilting co- 

 efficient. 



This is given by ^ lllan ^~f 1 =2.90±0.06, or± 2.01 per cent. 

 W llting Coen. 



The probable error of a single determination by this means was 

 found to be 8.3 per cent of the wilting coefficient. 



In the treatment of forest soils Bates (105), at the Fremont Ex- 

 periment Station, has found it necessary to use much larger carts 

 than those employed by Hilgard, and has also reversed the process, 

 so that the result is rather a measure of the ability of the soil to 

 hold the water of saturation than to lift water from below. A gal- 

 vanized can 5| inches deep and 4 inches in diameter, is filled to a 

 depth of 5 inches with air-dried soil, which is jarred and tamped 

 until no appreciable settling occurs. This can is perforated in the 

 bottom and a filter paper is used to keep the soil from sifting out. 

 The can is immersed to its full depth in water, but no water is al- 

 lowed to flow on the top of the soil. As the water rises from the 

 bottom by its own pressure, the air is pushed out, so that few, if 

 any. air spaces are left. The samples are allowed to soak at least 

 24 hours to insure complete absorption by the larger, permeable rock 

 fragments. 



The weight attained at the end of this period, or a longer period 

 if it appears necessary, is an index to the saturation capacity. 



The cans are now placed on a drain board, covered, and allowed to 

 stand for 48 hours. In rehandling the cans care must be used to 

 avoid jarring, as some of the water is held in a very delicate balance. 

 The amount of water held at this time is a measure of the capillary 

 moisture. In the vast majority of soils that have been treated, the 

 capillary moisture is about 90 per cent of the saturation capacity, 

 (lav does not affect this ratio appreciably, but humus increases it. 



The same cans are now used for the centrifugal test or moisture 

 equivalent determination, which will shortly be described. After this 

 they are oven-dried, to give the basis for dry-weight calculations. 

 The apparent density is also computed from the weight and volume 

 a tier this treatment. 



Tn 'Fable -i. there is presented a comparison of the capillary mois- 

 tures and wilting coefficients of L0 soils of one general type (granitic) 

 from an Engelmann spruce forest, but varying widely in state of 

 decomposition, clay content, and humus content. Each soil repre- 

 ample extending from the surface to a depth of I foot. The 

 wilting coefficients for Douglas fir and Engelmann spruce were mosi 

 carefully determined, the only objection thai might be brought 

 against the treatment being that the seedlings were given more direct 



