20 THE PHYSICAL ACTION OF LIME ON CLAY SOILS 



It may be readily observed that none of the salts affected the total 

 retentive power in the case of the salts run 100 days, with the exception 

 of the sodium carbonate. With the 225 day treatment, however, we find 

 that both calcium hydrate and limestone have caused a slight decrease 

 in water holding capacity. The precipitated carbonate may act in just 

 the opposite direction. The gypsum is without effect. 



DYE ADSORPTION STUDIES 



In the preliminary discussion, attention was called to the fact that 

 certain factors affecting dye adsorption have been entirely overlooked 

 in studies with, soils. Perhaps the most important of these factors are, 

 the stability of the dye, and the effect of salts on the adsorption equilib- 

 rium. There are, however, several other questions that arise in this 

 connection : 



What is the influence of the time of shaking on the adsorption equilib- 

 rium, and 



Does the mechanical agitation incidental to shaking tend to destroy the 

 flocculated condition, and hence affect the degree of adsorption? 



In order to study the effect of time of shaking, adsorptions were run 

 and terminated at regular intervals. Using two grams of Dunkirk silt 

 loam in methylene blue, it was found that complete equilibrium was 

 reached in from one to two hours. 



The effect of mechanical agitation on adsorption was studied by 

 adding two grams of soil to solutions in shaker bottles, the latter con- 

 taining the amount of salt that would be carried over in a two gram 

 charge of soil treated at the rate of 10 tons per acre. After shaking two 

 hours, a few cc. of a concentrated methylene blue solution was added, 

 and the shaking continued for five minutes longer. The results showed 

 that final equilibrium had not been affected by the salts present, with 

 the exception of the sodium and magnesium carbonate treatments, and 

 in these cases we do not have to postulate any change in stability of the 

 colloidal material, inasmuch as the solutions were very alkaline, and 

 hence could affect the adsorption equilibrium. The subject was studied 

 still further by running adsorptions in methylene blue, and determining 

 whether the final result was the same irrespective of the salt present. 

 Here again, the sodium and magnesium carbonates were found to increase 

 adsorption somewhat. 



Adsorption experiments with methylene blue were run as follows: 

 The equivalent of 2 grams of oven soil was weighed into the shaker 

 bottle containing 100 cc. of the dye (.25 gram per litre). After shaking 

 two hours, the clear supernatant solution was read against a standard. 

 The results with soils which had been limed for 100 and 225 days are 

 as follows: 



