THE CONSTITUTION OF THE SOIL 



possible to draw any exact line showing where these properties begin 

 to appear, but they entirely mask the effects of the silica and silicate 

 particles and obliterate the distinctions between sands, loams, clays. 

 Chalk soils, therefore, form a class by themselves to which, the ordinary 

 laboratory methods of analysis and investigation do not apply: un- 

 fortunately, appropriate methods have not yet been worked out. 



The Soil Water. 



The soil retains by absorption and surface attractions some 10 to 

 20 per cent, of its weight of water, distributed as films over its particles. 

 This water is of obvious importance as the medium through which 

 plants and micro-organisms derive their food, indeed the Whitney 

 school regard it as the culture solution for the plant. Its relationship 

 to the mineral matter is discussed by Cameron (68, 69). Notwith- 

 standing its importance, however, but little is known of it, because of 

 the difficulty of getting it away from the soil. No pressure method 

 has proved successful, but a centrifugal method which, however, has 

 not come into general use, gave the following results (Whitney & 

 Cameron (304)) : 



Instead of using this method the United States Bureau of Soils 

 investigates the solution obtained by stirring up soil with water, and 

 filtering under pressure through a Chamberland filter. The results 

 (304) are taken to indicate the following as the average composition of 

 the soil water : 



PO 4 NO 3 Ca K 



7-64 5-47 11-67 2274 per million of dry soil. 1 



The numerous analyses of land drainage water that have been 

 made in this country and on the Continent throw some light on 



1 The Bureau of Soils, prefer to express the composition in terms of dry soil, rather than 

 in terms of the solution. 



