EXPERIMENT STATION BULLETINS. 863 



KNO3, KCl, and CaCl., give a far more pronounced acid curve than 

 K0SO4, MgSO^, (NHJ0SO4, and NaHoC.O^. This, however, is naturally 

 to be expected since the products formed by the reaction between the 

 Ca(0H)2 and the acid or acid salt of these neutral salts possess different 

 degrees of dissociation or solubility. 



In considering the results on the effect of acids upon the lime require- 

 ment of soils, it was seen that when a soil, which showed a large lime 

 requirement was treated with an excess of dilute acid, the supernatant 

 liquid failed to give the acid curve, while the sediment did, but when the 

 sediment was washed, then the acid curve could no longer be obtained. 

 The natural and logical question now rises, do similar phenomena also 

 occur in the case of the salt solutions? 



The answer to this question was obtained by attacking the problem in 

 the same manner as before, namely, to several different soils, which 

 showed a high lime requirement, were added different salt solutions in 

 the ratio of 10 grams of soil to 50 c. c. of the solution of N/10 strength. 

 The mixture was stirred thoroughly for a few minutes, then allowed to 

 stand for about an hour until the supernatant liquid became clear. Then 

 some of the supernatant liquid was poured into the freezing tube without 

 filtering, and titrated with Ca(OH)o in the usual manner. It was found 

 that the depression began to increase immediately upon adding about 2 

 c. c. of Ca (0H)o, indicating that the supernatant liquid failed to give 

 an acid curve. Then the remainder of the solution was poured out and 

 the sediment was placed in the freezing tube and titrated with Ca(0H)2. 

 It was found that the freezing point depression decreased with the in- 

 creased addition of Ca(OH)o until a certain point was reached and then 

 commenced to rise. The results then plotted into an acid curve, and 

 proved that the soil contained an acid or acid salt or some substance 

 which was not equally or proportionally represented in the supernatant 

 solution. In another sample of soil similarly treated, the sediment was 

 washed v/ith water and then titrated. In this case the freezing point 

 depression remained constant up to a certain point and then began to 

 rise. The results, then plotted into an absorption curve, and proved that 

 the substance which gave the acid curve above was washed away with 

 water. 



These experiments tvere repeated with many of the neutral salts using 

 different soils, and in every case the results tvere the same, namely the 

 superrnatant liquid failed to give an acid curve while the sediment did, 

 hut when the sediment was washed then it no longer yielded an acid 

 curve. 



These results then agree perfectly with those obtained with acids, and 

 whatever is the explanation for the one case is true also for the other. 



Since no mineral soil out of a number of 80 tested for lime require- 

 ment in their natural condition gave an acid curve but only an absorption 

 curve, and inasmuch as the free acid and acid salt produced in these soils 

 when they were treated with neutral salts or acids and acid salts, were 

 carried away by washing and the soils then gave an absorption curve, it 

 seems safe and logical to conclude that the presence of soluble acids, or 

 acid salts in the mineral soils under field conditions is only temporary 

 and probably never permanent. The acidity or lime absorption of the 

 mineral soils, therefore, is probably due mainly, if not entirely, to the 

 insoluble acids of the soil, the silicic acid, acid alumino-silicate, and 



