RESEARCH METHODS IN STUDY OF FOREST ENVIRONMENT. 



75 



for the v ell soil, can never be considered as an exact measure of the 

 moisture outside. The well samples will be principally useful in 

 showing changes, and without doubt should occasionally be compared 

 with native samples taken near by. It is believed, however, that for 

 practical purposes a certain constant relation between the two soils 

 may be assumed. So far, because of the great difficulty of actual 

 contact tests between two soils, the moisture ratio at equilibrium 

 must be established on theoretical considerations. 



From what is known of capillary movement in soils (116) it would 

 seem that, when the moisture content of two soils is near the satura- 

 tion point, they will be in equilibrium at moisture values measurable 

 bv the amount which either soil can hold against the force of gravity. 



Similarly, at much lower moisture contents, the amounts which 

 the two soils hold against a force one hundred or one thousand times 

 as great as gravity, would appear to establish a basis for equilibrium. 

 But, in view of the fact that at a low-moisture content actual capil- 

 lary movement becomes negligible while transfer from one to the 

 other by the rapor-transfer method can be readily accomplished, it 

 seems more logical (hat we should consider an equilibrium existing 

 which would mean equal osmotic pressures in the I wo soils. These 

 points can be determined tor each soil by freezing-point depressions 

 or by assuming equal osmotic pressures ;i( l he willing coefficients. 



Diagram 3 -how- ;i method for working out n 9cale of relations for 

 the -oil of any well and -oil from three depths, obtained when the 



well was 'lug. The curve for the well soil is :i straight line whose 



