SOIL SOLUTION 7 



power of the water — into which will enter the factor of 

 carbon dioxide content — but also, and perhaps most largely, 

 on the nature and amount of the soil colloids. The colloids 

 retain salts by adsorption, and in contact with free water 

 the partition of salts between the colloids and the liquid 

 depends on the amount of liquid present, that is on the 

 dilution of the solution. The composition of the soil 

 solution therefore varies with the amount of moisture in the 

 soil, and of course this is constantly changing. 



The methods which have been employed to separate the 

 soil solution are discussed by Stiles and Jorgenson (19 14), 

 and may be summarised here, («) Collection of drainage 

 water from field drains, (b) Collection of water run slowly 

 through a column of soil. Only the first portion coming 

 through is taken as representing the water originally present 

 in the soil. This method is in effect a collection of artificial 

 drainage. Some investigators have used liquid parafiin to 

 displace the soil water, (c) Extraction of a definite weight of 

 soil with a definite amount of solvent— either distilled water 

 or an acid, (d) Removal of the soil moisture by high centri- 

 fugal force, (e) Squeezing out the solution by high pres- 

 sure. ( / ) Drawing the solution into a porcelain filter candle 

 by suction, (g) Recently attempts to estimate the concen- 

 tration of the soil solution have been made by determining 

 the lowering of the freezing-point of the moisture in the soil. 

 It will be seen that the first three methods do not give a true 

 sample of the solution present in the soil, though they have 

 a certain use for comparative purposes. The second three 

 do extract the soil solution but only a fraction, the size of 

 which will depend on the precise condition of soil and of 

 experiment. 



The kind of result obtained by three of these methods 

 is shown in Table I. The soil in each case is a loam, though 

 of different origin. The figures are taken from Russell's 

 book, " Soil Conditions and Plant Gro^\1;h." 



