THE PHYSICAL ACTION OF LIME ON CLAY SOILS 5 



amount of salts released by the current bears only a very indirect rela- 

 tion to the amount of colloidal material. 



5. The "Pouillet Effect" is another means by which the estimation 

 of internal surface has been attempted. This method is named after C. 

 Pouillet, who as far back as 1823 observed that finely divided substances 

 released heat on wetting. Mitscherlich (1S98) was the first to attempt 

 the estimation of the internal surface of soils by the use of this phe- 

 nomenon. Several other investigators have since then attempted similar 

 studies. The fact that heat release in soils may be associated with a 

 number of factors renders the Pouillet effect of doubtful value. 



f>. The total retentive power of the soil for water has long been used 

 as a standard measurement. The early investigators usually allowed 

 water to rise by capillarity in a cylinder filled with the soil, and then 

 determined the final percentage present. Hilgard modified the procedure 

 by using a short column of standard length, but the method still remains 

 rather inaccurate. 



The investigations of Trentler, Wollny, Blanck, and Engels indicate 

 that calcium oxide increases the total retentive power of the soil. All 

 these men, however, used excessive applications. The probable error in 

 the case of Timer's work is too high to permit the drawing of conclusions. 

 Frear thinks that liming has no effect on the total retentive power. The 

 writer is calling, attention in each case to the instances in which limed 

 soils have been used, for there is no better criterion as to the accuracy 

 of a physical method, than its sensitivity to small amounts of lime. 



7. The Moisture Equivalent Method of Briggs and McLane suggests 

 itself as a possible means for estimating internal surface. Unfortunately, 

 the probable error is so high as to probably preclude the measurement 

 of very small lime applications. Sharp, of the California Station, is using 

 this method at the present time in his alkali investigations. 



8. The capillary rise of water in soil columns has been used by 

 several investigators as a method for estimating soil colloidality. The 

 usual procedure has been to place the lower end of a column of dry soil 

 in contact with water, and record the speed and total height of ascent. 

 Meve^ Krawkow, Gross, Blanck, and Engels have performed capillary 

 experiments with lime treated soils. The data, considered as a whole, 

 is inconclusive. Undoubtedly, internal surface is a factor in capillary 

 rise, but the additional factors of surface tension and degree of compac- 

 tion are exceedingly difficult to control. 



9. The speed of percolation of water through soils has frequently been 

 used as a measure of soil structure. Studies have been conducted by 

 Yogel, Ebermeyer, Bfihler, Blanck, Thaer, and Engels on the influence 

 of lime on percolation. All agree that lime increases the ease with which 

 water passes downward. For comparative purposes it is necessary to 

 obtain a large volume of percolate, and this results in the removal of 



