EXrERlMENT STATION BULLETINS. 69r. 



seems to aironl a conclusive proof of this priuciple. The recent inves- 

 tigation of Jordan*, Burd, Stewart and Hoagland^ also lead to the same 

 conclusions. 



It may be stated tlien as a general principle that while the solubility 

 factor is not an a1)solute and reliable criterion for the state of fertility 

 of a soil, a very rich or heavily fertilized soil tends to give a higli 

 solubility product or a high soluble salt content. 



Mention has been made that in employing salt treatments in tlie study 

 of the rate and extent of solubility it was hoped to be able to throw some 

 light on the character of the reaction between soils and salts — i. e. — 

 whetlier it is chemical or physical. As is well known, this question still 

 remains unsolved and the scientific opinion on it is very mucli divided. 

 Some believe that the action is chemical, others that it is physical. 

 It was thought, therefore, that the study of the rate and extent 

 of solubiliy of treated soils might help to solve this problem. It was 

 reasoned that if the reaction was chemical so that the salt or its ion 

 combined with the soil to form new chemical compounds, the rate of 

 solubility of tliis treated soil should be slow and gradual since the rate 

 of solubility of many definite soluble compounds such as CaH^(POJo, 

 KoSO^, etc., is slow and gradual. If on the other hand, the reaction 

 is physical so that the salt or its ion was merely absorbed or condensed 

 on the surface of the soils, probably in a fihn form, then the rate of 

 solubility of the soil should be very fast and the equilibrium sliould be 

 attained in a very short time probably in a few minutes. The latter 

 reasoning was supported by the fact that an adsorbed film should go 

 into solution faster than a difficult soluble chemical compound and espe- 

 cially since an adsorbed material generally follows the law of equal 

 distribution, i. e., between the solid and liquid phase. 



If the difference in the rate of solubility of salt treated soils is a true 

 criterion for distinguishing between chemical and physical reaction then 

 the evidences are overwhelmingly in favor of the theory that the reaction 

 between soils and salts or their ions is chemical and not physical. For 

 it is readily seen that in all the soils with all the salts the rate of solu- 

 •bility is very slow and gradual, extending usually to GO days and in 

 some cases even to 120 days. This chemical theory is further supported 

 by the chemical composition of the material going in solution. As al- 

 ready stated this material consists of the base radical of the salt added, 

 of iiluminum, iron, calcium, magnesium, phosphorus and organic matter. 

 Now if the reaction were ])hysical, the resulting solubility product ought 

 to be composed largely of the material adsorbed. 



Referring' once more to the experimental data, the questions may be 

 asked, has the solubility attained equilibrium and has the solution be- 

 come saturated ? 



Before an attempt is made to answer these questions it is necessary 

 to recall that the soils were kept in stoppered glass tubes at a moisture 

 content of about 1 of soil to about .70 water. These conditions of the 

 experiment, therefore, were very favorable for maximum true solubility 

 but very unfavorable to nitrification actions, although perhaps some- 

 what favorable to denitrification and to other types of biological action. 

 It is believed, however, that under the condition of the experiment bio- 



(4) X. Y. state Agr. Bxpt. Sta. Bui. 424. (1916) 



(5) Journ. Agr. Res. V. 12, No. 6 (1918), 



