6 THE PHYSICAL ACTION OF LIME ON CLAY SOILS 



salts from the sample. An objection to this procedure rests in the fact 

 that the colloidal condition, the factor Avhich we are measuring, depends 

 on the salt content. A decrease in the amount of adsorbed salts results in 

 a deflocculation of the soils. Both Mayer and Van Bemmelen noted at an 

 early date that percolation decreased on prolonged leaching, and the same 

 thing has been more recently noted by Hall, and by Sharp. 



10. The Atterberg Plasticity Method has been proposed solely as a 

 means of evaluating clays. It has never been applied to the estimation 

 of internal surface. According to Kinnison, the Atterberg plasticity 

 figure depends on too many factors to be of value. 



11. The term "hygroscopic moisture" has usually been taken to mean 

 the amount of water that a soil will absorb in order that its internal 

 surface be covered with a film one molecule in thickness. However, there 

 is reason to believe that the thickness of the film is greater than that 

 stipulated by the definition. Furthermore, the slowness in reaching 

 equilibrium, and the great effect of temperature on the final result, indi- 

 cate that much of the water is present in the form of capillary water 

 located in the interstices of the soil particles. It is more correct to speak 

 of the phenomenon as "hygro-interstitial moisture," connoting thereby its 

 true nature. 



The early workers tested out the adsorptive power of soils for various 

 vapors and gases. All these investigations resulted in the selection of 

 water vapor as best suited for the purposes in hand. The hygro-inter- 

 stitial investigations have been conducted according to two general types 

 of procedure : 



1. The first involves the constant passage of water vapor over or 

 through a soil until equilibrium is reached. 



2. The second requires the placing of the sample in an atmosphere 

 whose degree of saturation is controlled, the moisture being conveyed to 

 or from the soil by diffusion. 



The classical investigations of Ammon and of von Dobeneck belong to 

 the first type. They conducted the saturated vapor through a U-tube or 

 some other suitable vessel containing the soil, until equilibrium had been 

 reached. Both men were concerned with the adsorptive power of the 

 various soil constituents, and so carefully was their work conducted, that 

 it remains today our most valuable contribution to the subject. 



One of the difficulties with the procedure was the frequency with which 

 an abnormal condensation of water vapor occurred on the interior of the 

 containing vessel. This led to the practice of reducing the degree of 

 saturation of the water vapor. Heiden, for instance, employed a vapor 

 a.pnroximatoly seventy-five per cent saturated, but he could not obtain 

 valuable results. Owing to the difficulties of manipulation the subject 

 was abandoned, and during the nineties no work was done on any phases 

 of the question. 



