EXPERIMENT STATION BULLETINS. 337 



chemical treatments. The magnitude of fixation evidently depends upon the 

 nature of the chemical compound used in treating the soils; its manner of 

 dissociation, the solubility of the resulting products, and the quantity rela- 

 tionship between the reacting components. As the foregoing factors vary 

 different chemical systems would be set up between the reacting materials. 

 Providing the reactions under consideration are chemical, chemical laws and 

 theories should be applicable. It must be remembered, however, that 

 soils are very hetrogeneous substances and they cannot be expected to sub- 

 mit to manipulation as might be the case with chemically pure substances. 

 Many difficulties stand in the way of a clear interpretation of results. We 

 know as yet very little concerning the chemical constitution of the soil. Very 

 little is known concerning the effects of added salts on the solubilities of soil 

 components, the possibility of the formation of double salts, the effect of re- 

 action of soil media upon solubilities, and the possibility of secondary reac- 

 tions. Further work along intensive lines is necessary l)efore a complete 

 understanding of the relationships involved can be obtained. 



A law of reaction between chemicals and soils may then be formulated 

 from the foregoing results and conclusions. An ion of any soluble salt that 

 forms an insoluble comijound with soil components will be fixed in soils 

 from solutions of the salt, and if soluble combinations are formed during 

 the reaction they will appear in the soil solution or extract. When salts 

 that dissociate into ions are placed in contact with wet soils the fixation of 

 the cations depends upon the resulting combination of the anions; i. e. fix- 

 ation and liljeration of elements are equivalent; and when alkaline salts 

 that dissociate into molecules are placed in contact with wet soils fixation 

 from one molecule is independent of the fixation from or combination of 

 the others. This law may be stated more specifically when the class of the 

 dissociating compound is known. In general fixation and liberation of 

 elements, under the foregoing conditions, depends upon the manner of 

 dissociation of the chemicals used in soil treatments and the solubilities 

 of the compounds formed, and the magnitude of fixation depends upon 

 the quantity relationships between the reacting components. The power 

 of a soil to fix cations may be increased by bringing it into contact with 

 hydroxides or alkaline salts in solution, and decreased by acid and acid 

 salt treatments; but neutral salts very in their effects on this soil character- 

 istic, causing either no equivalent change or an increase depending upon 

 the elements involved. 



TIIIE SOIL REACTION 



Results obtained in this investigation may be interpreted as to give a 

 Ijetter understanding of the phenomena of soil reactions particularly with 

 respect to the mineral portion of the soil. Basing conclusions on these 

 results it may be said that practically all soils have acid and basic proper- 

 ties in conunon because they neutralize acids and also alkalies. In general, 

 all soils decompose neutral and hydrolizing salts, at least the common salts 

 of these classes. A general similarity in these respects exists between acid 

 and alkaline soils. (Litmus paper test.) The differences noted were in 

 magnitude only, and these differences in magnitude were practically all 

 in favor of the alkaline soils over acid soils of similar classes. From a quan- 

 tity standpoint, however, certain acid soils may show a greater magnitude 

 of reaction with chemical compounds than certain other alkaline soils, because 

 the degree of change dejiends upon the quantity relationships. Therefore, 

 43 



