EXPERIMENT STATION BULLETINS. 627 



with an exchange of bases, and the other is based upon a physical selec- 

 tive adsorption of the base of a salt with a resulting acid which dis- 

 solves an equivalent amount of the soil bases. In the first theory it is 

 assumed that a neutral salt reacts with the polysilicates of the soil with 

 the base becoming fixed or insoluble and an equivalent amount of an- 

 other base being replaced thus: Alx Fex Mgx Nax Ca(SiO,)x (H.,0) 

 + 2KC1 = Alx Fex Mgx Nax K2(Si03)x (H,0) + CaCl.. This equa- 

 tion typifies the metathetical reaction that may take place between a 

 neutral salt and the zeolitic compound of the soil. The CaCL is sup- 

 posed to be in solution. 



The fixation of the soluble jihosphates is supposed to be accomplished 

 by the bases present in the soil, such as iron, aluminum, tetanium, lime, 

 and magnesium. The reaction which is different from the above is 

 typified bv the following equation : 



CaH^lPOJ. + CaCO., = Ca.H.,(POJo + CO. + H..O. 

 Ca,Ho(POJo + CaCbg = Ca,{FO,)., .+ CO, + H.O. The soluble 

 phosphate, therefore, reacting with calcium forms insoluble Ca3(P04)..,. 

 According to the physical selective adsorption theory it is suggested 

 that when a soil is in contact with a solution such as KCl it adsorbs 

 the potassium ions at a much greater rate or greater proportion then 

 the chlorine ions thereby, (since an equivalent number of hydroxyl ions 

 are also removed with the potassium ions), causing a partial hydro- 

 lysis of the solution, (KCl + HOH = KOH (adsorbed) + HCl), and 

 leaving free acid in the solution which goes to dissolve the soil bases. 



Although the last theory might be correct, yet it has not been abso- 

 lutely proven and does not account for all the facts. The first or chem- 

 ical theory, however, which seems more rational, explains practically 

 all the facts quite satisfactorily and is probably more widely accepted. 

 In the light of this theory tlie foregoing question : How is the increase 

 in concentration of the soil solution by the soluble salts brought about? 

 and. What might be the composition of the resulting soil solution?, are 

 explainable, af least partially. For instance, the increase in concentra- 

 tion of the soil solution may not be due to the direct addition of the 

 concentration of the salt solution but that a new compound or com- 

 pounds might be formed which are in solution and have smaller than 

 or as great lowering of the freezing poiut as the salt solution added, 

 and that not any of the salt solution added may exist in the original 

 form in the resulting soil solution. 



It would be a remarkable coincidence, however, if a new compound 

 was formed in the various mineral soils to which Ca(NO,).; was added, 

 which had a lowering of the freezing point as great as this salt solution 

 itself. In a case of this character one is almost led to believe that 

 the entire concentration of this salt solution was simply added to the 

 soil solution without undergoing any change, just as in the case of 

 quartz sand, where the increase in concentration of its solution is due 

 to the direct addition of the concentration of the salt solution. 



The almost complete disappearance of the original concentration of 

 CaH,(PO,)o. NaoHPO^, and KoHPO^ solutions in some of the soils tends 

 to confirm the equation already given that these compounds react with 

 the bases of the soils and form insoluble substances and thus the con- 



