EXPERIMENT STATION BULLETINS. 601 



ing equation CaH,(POJo + CaCO., = CaoH^POJo + CO^ + 

 HoO. Ca.H.(POJ, + CaCOa = CaoCPOJo + CO, + H,0. The solu- 

 ble phosphate, therefore, reacting with calcium forms insoluble Ca3- 

 (POJ, 



According to the selective adsorption theory (19) it is suggested that 

 when a soil is in contact with a solution such as KCl it adsorbs the K ion 

 at much greater rate or greater proportion than the CI ion, thereby, 

 (since an equivalent number of hydrox3'l ions are also removed with the 

 potassium ions), causing a partial hydrolysis of the solution, (KCl plus 

 HOH = KOH (adsorbed) -f HCl), and leaving free acid in the solu- 

 tion w^hich goes to dissolve the bases in the soil. 



Although the last theory might be correct yet it has not been absolutely 

 proven and does not account for all the facts. The first or chemical 

 theory, however, which seems more rational explains practically all facts 

 quite satisfactorily and is probably more widely accepted. In the light 

 of this theory the answer to the above question as to how the increase in 

 concentration of the soil solution by the application of salts is brought 

 about and what the composition of the resulting solutions is may be found 

 in the assumption that similar chemical reactions as shown above took 

 place between the constituents of the soil and the salt solution added 

 with the formation of entirely new compounds which have a smaller 

 than, or as great, lowering of the freezing point as the salt solutions 

 added, and that not any of the salt solutions added may exist in the 

 original form in the resulting solution, except possibly in the artificial 

 inert substances such as the quartz sand, kaolin, burned soils, etc. In 

 these latter substances the entire original concentration of the salt solu- 

 tions was imparted to them and remained almost unaltered. 



The almost complete disappearance of the original concentration of 

 the CaH4(P04)2 and K2IIPO4 solutions in the agricultural soils tends 

 to confirm the equation given above which shows that these compounds 

 react with the bases of the soil and form insoluble substances and thus 

 the concentration of the soil solution is very little if any increased 

 either directly by these compounds or by the formation of new com- 

 pounds, as in the case of the neutral salts. 



The results obtained with the acids can be explained under the same 

 basis as those of the salts. These acids reacted with the bases of the 

 soils and formed salts. The degree of concentration imparted to the 

 soil solution depends upon the freezing point depression of the salt 

 which in turn depends upon the amount of the salt in solution and its 

 degree of dissociation. The slight or negligable increase in concentra- 

 tion which the oxalic acid caused in the agricultural soils and especially 

 in the heavier types, suggests the idea that the compound formed was 

 more or less insoluble, similar to the case of the acid phosphate salts. 

 The increase in concentration of the acietic acid above that of the origi- 

 nal concentration of the acid itself signifies that either this acid formed 

 a compound in large quantity or one which had a far greater degree of 

 dissociation than the acid itself. The latter assumption is more 

 probable. 



Finally, it should be remembered in drawing conclusions concerning 

 the eff'ect of the application of salts and acids upon the concentration 

 of the soil solution that the lowering of the freezing point which is em- 



(19) Parker, Jour. Agr. Res., V. 1 No. 3, 1913. 



