THE PHYSICAL ACTION OF LIME ON CLAY SOILS 7 



In 1903, Kodewald and Mitscherlich proposed a method corresponding 

 to the second type of procedure outlined above. The soil sample, pre- 

 viously dried over phosphorus pentoxide, was placed in a container over 

 ten per cent sulfuric acid until equilibrium was attained. The function 

 of the sulfuric acid was to control the degree of humidity and prevent 

 condensation. This method has been used by a large number of investi- 

 gators. Engels, Timer, and Czermack have found that lime, particularly 

 calcium oxide, decreases the hygro-interstitial moisture. The amounts of 

 lime which they used, however, were excessive. 



Comparisons of the Rodenwald-Mitscherlish method with the other 

 means of measuring internal surface have been attempted by Tadokoro, 

 and Stremme and Aarnio. They find a good general agreement between 

 the different methods. It should be pointed out in this connection, how- 

 ever, that a good general correlation is to be expected in comparing soils 

 whose percentages of clay vary widely. 



The possibility of the desiccation over phosphorus pentoxide having an 

 influence on the colloidal material has been pointed out by Ehrenberg 

 and Pick. They suggest that moist soil be placed in the desiccator or 

 humidor and allowed to remain until equilibrium is obtained. 



There are two main objections to the Rodewald-Mitscherlich method and 

 its modifications: 



1. Too much time is consumed in waiting for equilibrium to be reached 

 in any particular case. 



2. There is a high probable error in the method, due probably to the 

 fact that diffusion permits only an approximation of true equilibrium 

 conditions. 



Blanck ran soils according to the Ehr en berg-Pick modification in one 

 instance for a period considerably exceeding one hundred days, at the 

 end of which time equilibrium had not been reached. 



12. The Dye Adsorption Method constitutes one of the standard means 

 for determining the internal surface of soils. 



Undoubtedly, there exists in the soil a great variety of colloidal sub- 

 stances varying in both chemical and physical condition. Four forms, 

 namely, iron, aluminum, humus, and silica, have been generally recog- 

 nized. This classification is of the crudest sort, and undoubtedly comes 

 far from conveying an adequate conception of the variety of colloidal 

 materials present. When we recall that the weathering processes usually 

 increase the amount of colloidal matter, we might expect to find about 

 as many colloids present in the soils as original rock sources. Kogers has 

 made a review of the mineral kingdom, and finds a great number of min- 

 erals to be colloidal in nature. Many of them, we have reason to believe, 

 exist in the soil, as, for instance, allophane, elemental carbon, opal, hema- 

 tite, and limonite. Soils of volcanic origin probably contain pyrolusite 

 and rutile. 



