B. A. Keen 413 



Although it seems more probable that the actual curve is similar to 

 that given in Fig. 4 when Y„ = 9, yet if it be assumed that one of the 

 lower curves is nearer the truth, there will be a certain amount of total 

 water, for which the amount of unfree water is a maximum. It is 

 suggestive to associate this point with the "optimum water content" 

 of the soil, at which point, according to Cameron and Gallagher^, various 

 physical properties of the soil, such as specific gravity, resistance to 

 penetration, rate of warming, etc., reach either a maximum or a minimum 

 value. 



This discussion as to the most probable type of curve expressing the 

 relation between free and unfree moisture is put forward with reserve, 

 owing to the very general nature of the possibilities considered. The 

 essential point of the foregoing is that one equation defines the moisture 

 over the whole range, and hence these various constants and critical 

 points represent equilibrium points only, and do not indicate breaks in 

 the physical state of the water in the soil, a conclusion in harmony with 

 that advanced by the present writer in connection with the evaporation 

 of water from soil. 



Many other possibilities as to the behaviour of the soil solution 

 could be considered in the light of the present results, but the discussion 

 would necessarily be of a broad nature, and depend on the approximate 

 truth of the initial assumption made in this paper — that the freezing- 

 point depression is inversely proportional to the free moisture content. 

 Hence it does not seem profitable to enter into this aspect of the question, 

 until further information is obtained on this and allied assumptions. 

 Sufficient data have been presented, however, to show that the freezing- 

 point method of examining the soil solution demonstrates that the 

 relations between soil and the moisture content are of no simple type, 

 but that a complex connection holds in a continuous manner over a 

 wide range of water content. 



Summary. 



An examination has been made of some of the extensive experi- 

 mental data obtained by Bouyoucos and his associates on the freezing- 

 point depression of soil solution at varying moisture contents, examined 

 in situ. 



These workers find that the soil solution in quartz sand and extreme 

 types of sandy soil obeys approximately the same law as dilute solutions — 

 1 U.S. Bureau of Soils. Bull. No. 50 (1908). 



