THE PHYSICAL ACTION OF LIME ON CLAY SOILS 13 



sary to stipulate any other action to account for the surface phenomena 

 which take place. 



A consideration of the literature on the effect of lime salts on floccula- 

 tion reveals an unusual amount of confusion. The relation of valence to 

 flocculating power has long been appreciated, but unfortunately invetiga- 

 tors are just coming to realize that the question of active masses is of 

 equal importance. For instance, sodium salts of weak acids are floccu- 

 lents or defiocculents according to the relative concentrations of pre- 

 cipitant and material being precipitated. This question has been dis- 

 cussed in detail by Given, Wolkoff, and Wiegner. 



Rohland believes that on liming, the precipitating power is due to 

 hydroxyl ions, and with calcium hydrate, the action is direct. With cases 

 in which gypsum is applied, Rohland would assign the beneficial result to 

 the precipitating power of the hydroxyl ions formed on the decomposi- 

 tion of the salt. Here again, the various colloidal materials present in 

 the soil tend to further confuse the phenomenon. Pappada finds that 

 the hydroxyl ion is the most powerful in the precipitation of hydrous 

 ferric oxide. Rohland's view would hold in so far as the positive colloids 

 are concerned, but it would not hold for the negative. A soil suspension 

 is usually negative, but there is no ground to believe that the colloidal 

 material in the soil is entirely precipitated by cations or other bodies 

 positively charged. 



Ehrenberg holds that the cation is the important flocculating agent. 

 He ascribes a strong action to the calcium ion, and virtually none to the 

 hyfroxyl. Therefore 1 calcium hydrate is the strongest flocculent of the 

 lime salts. On increasing the strength of the acid in the salt, the pre- 

 cipitating action becomes less and less, until in the case of gypsum, we 

 have practically complete antagonism. Ehrenberg's theory is better than 

 Rohland's just in so far as it better describes the actual state of affairs. 

 As a matter of fact, both views are extreme. A solution of the question 

 lies in the recognition of the complex nature of the colloidal material, 

 and the fact that flocculation is a matter of relative charges, masses, 

 and valencies. 



In past studies on the physical effect of lime on the soil, the tendency 

 has been to make applications on a percentage basis. For example, a 

 favorite custom has been to use one per cent of lime, and there is one 

 instance in the literature in which one part of lime was added to four 

 parts of soil. In view of the relation of masses to precipitation, and 

 furthermore, the wide departure from field practice involved, the question 

 naturally arises whether the results from such experiments are particu- 

 larly significant. The work of Blanck, Thaer, and Engels, the lime 

 studies most frequently quoted, are all open to the objection that the 

 applications used were excessive. Unfortunately the methods available 

 for physical studies have not been sufficiently accurate to be used in 



