10 THE PHYSICAL ACTION OF LIME ON CLAY SOILS 



a. The dye is taken up most readily in an acid solution but may be 

 taken up in a neutral or alkaline solution. 



b. A readily adsorbed anion decreases the amount of dye taken up. 



c. A readily adsorbed cation increases the amount of dye taken up. 

 The effect of the reaction on dye adsorption has been extensively 



studied by Bancroft, and by Pelet-Jolivet and his co-workers. If the 

 amount of salt in a sample of soil is large, the final equilibrium may be 

 affected. In order to use the dye method as a measure of internal sur- 

 face, we must satisfy ourselves by preliminary experimentation that the 

 salt is present in too small an amount to influence the degree of adsorp- 

 tion. It is readily apparent that we should use small charges of soil, 

 particularly if fertilizers have been added, for the amount of salt per 

 unit concentration of dye increases directly with the amount of soil 

 used. Ruprecht and Morse in their ammonium sulfate studies, found 

 that the amount of dye taken up by the soil was increased after fertilizer 

 treatment. We have no means of knowing from their work, however, 

 whether the increase was due to the influence of the ammonium sulfate 

 on internal surface, or whether it was the result of the changed reaction 

 of the bath. The effect of the added material on the adsorption equili- 

 brium has been in the past entirely overlooked in soils work. 



5. The protective action of organic matter on colloidal material has 

 been recognized by a number of investigators. In running experiments 

 on mineral colloids it is desirable to use soils as free from organic matter 

 as possible. 



13. Selective adsorption has been used by many investigators as a 

 means of estimating internal surface. Heiden, Parker, and Konig, 

 Hasenbaumer, and Hassler are only a few of those who have taken the 

 adsorptive power of the soil for potassium as a measure of the internal 

 surface involved. The results lose their significance, however, when we 

 recall that the soil contains a number of different kinds of colloidal 

 material, each varying in its specificity with regard to adsorption. Thus, 

 Thaer finds that the potassium ion is not adsorbed by colloidal humus, 

 and Lokolovskii observes the same thing for the ammonium radical. 

 Daikuhara believes that the adsorption of the potassium ion is character- 

 istic of the colloidal iron and aluminum. The possibility of interchange 

 of bases tends to further confuse the phenomenon. It is, therefore, not 

 surprising that some workers, as Tadokoro, have failed to establish an 

 agreement in the results from selective adsorption and some of our other 

 more valuable methods. 



14. The Histological Method for the determination of colloids in clays 

 was proposed by Endell. The dry clay is boiled in Canada balsam, and 

 after cooling and hardening it is cut into small sections and colored with 

 fuchsin. This method has been discussed by Cornu. Owing to the sim- 



