THE PHYSICAL ACTION OF LIME ON CLAY SOILS 



silica. Methylene blue, while adsorbed slightly by humus and aluminum, 

 is taken up in such enormous amounts by silica, that it may be rightly 

 considered specific for the latter. The writer has found eosin to be 

 admirably adapted for aluminum. No dye has yet been found which is 

 satisfactory for hydrous ferric oxide. Summarizing, then, we have the 

 following as the best suited for soils adsorption work. 



Hydrous ferric oxide, no dye. 



Hydrous aluminum oxide, eosin and diamine sky blue. 



Humus, safranine. 



Silica, methylene blue. 



2. The concentration of the dye employed should be small. Within 

 narrow limits, adsorption is a linear function of the concentration. The 

 curve obtained by plotting the amount adsorbed against concentration 

 ceases to be linear, however, on increasing the concentration of the dye 

 solution. Further, the stability of the sol may be affected if the dye is 

 too concentrated. 



3. The dye should be stable irrespective of the reaction of the bath. 

 All dyes which in alkaline solution are changed into the dye-base or 

 ICMK-O -base are unsuited for soils which give an alkaline filtrate on wash- 

 ing. Inasmuch as the great majority of soils render an aqueous solution 

 alkaline, all colors exhibiting the above characteristics, as the tri-phenyl 

 methane dyes, for instance, should be discarded. Unfortunately, this 

 includes the greater portion of the colors used in the past, as crystal, 

 methyl, and gentian violet, aniline blue, aniline green, aniline red, methyl 

 green, malachite green, etc. Changing the reaction of the solution after 

 adsorption is usually not sufficient to restore the color to the dye, since 

 alkalinity may reduce the dye-base to the leuco form. Oryng, and Adams 

 and Rosenstein have called attention to the difficulties inherent with the 

 triphenyl methane dyes. It is not surprising that Gedroits, using crystal 

 and methyl violet, found no relation between colloidality and adsorption. 



Another potential source of error lies in the fact that alkali may unite 

 with the dye and form a lake. This is what happens in the case of alizar- 

 ine, one of the dyes recommended by Ljollema. Tadokoro, in selecting a 

 color for his work, chose eosin, because it was stable in acid or alkaline, 

 but he overlooked the fact that eosin is specific for hydrous aluminum 

 oxide. We probably obtain no eosinic lake formation in the case of 

 adsorption by soils. Too much care cannot be taken that the dye is 

 stable under all conditions. 



4. The reaction of the solution should not affect the adsorption equili- 

 brium. In the textile industries the amount of dye taken up in any 

 particular case is largely determined by the degree of reaction of the 

 bath. The subject is summarized by Bancroft as follows : 



The following holds for an acid dye: 



