1917] SOILS FERTILIZERS. 211 



tude or direction of the freezing point depression. The method is based upon 

 the following principles: (1) The freezing point depression of a soil contain- 

 ing a soluble acid or acid salt decreases upon adding various quantities of 

 Ca(0H)2 up to a certain point and thereafter increases with further addi- 

 tions. This point is considered to be the point of neutralization of the acid 

 or acid salt and of the saturation of the soil for lime. (2) The freezing point 

 depression of a soil containing neither a soluble acid nor an acid salt but pos- 

 sessing an absorptive power for lime remains constant as Ca(0H)2 is added 

 up to a critical point and thereafter rises with further additions. The critical 

 point is considered to be the saturation of the soil for lime. (3) The freezing 

 point depression of a soil already alkaline and saturated with bases starts to 

 rise almost immediately upon the addition of a small amount of Ca(0H)2. 



The results showed that the amount of lime taken up by soils varied greatly. 

 The freezing point method gave much higher lime requirements than the Veitch 

 method, and appeared to indicate the true maximum lime requirement of soils. 

 "The absorption curve of the mineral soils signifies that the Ca(OH)2 is taken 

 out of solution and is rendered inactive as far as the freezing point depression 

 is concerned. The substances which accomplish this are in the solid phase. 

 . . . The absorption curve also indicated that there is no basic exchange in 

 soils, when a hydrate is employed, until the soil is satisfied or saturated with 

 the base." 



Most of the few peats tested gave evidence of acidity and took up calcium, 

 potassium, sodium, and ammonium hydroxids in equivalent amounts. 



" When a soil ceased to take up one base it took up very little if any of 

 another base, or if it did it released a corresponding amount of the one with 

 which it was already saturated. On the other hand, when a soil still absorbed 

 one base it absorbed a corresponding quantity of another. The addition of 

 acids and acid salts increased the lime requirement of soils. The magnitude 

 of the increase was approximately equal to the amount of lime required to 

 neutralize the quantity of the acid or acid salt added. . . . 



" When a soil was treated with an excess of acid and then washed, the lime 

 requirement was also increased, but the results plotted into an absorption 

 curve. When a soil which showed a high lime requirement was treated with 

 an excess of acid the clear supernatant liquid failed to give an acid curve, 

 indicating that it contained very little if any acid. The litmus paper tests 

 showed that it was very nearly neutral. The sediment, however, gave an acid 

 curve, signifying that it contained a considerable amount of acid. . . . When 

 this sediment was washed with water, however, the acid curve could no longer 

 be obtained, showing that the acid was washed away." The same was observed 

 with salts in solution. 



"All soluble salts increased the lime requirement of soils, but the magnitude 

 of the increase was greater in the case of the neutral salts than of the acid 

 phosphate salts." 



The conclusion is drawn that " the presence of soluble acids, or acid salts, in 

 the mineral soils under favorable natural conditions is only temporary, if ever 

 present, and never permanent. The acidity or lime requirement of soils, there- 

 fore, seems to be due mainly to the insoluble acids of the soil, the silicic acid, 

 silica, acid alumino-silicates, and perhaps to the insoluble organic matter. 

 There appears to be then practically no active acidity in the mineral soils, but 

 only negative. Exceptions to these general statements are probably very few. 

 In the peats and mucks, however, the formation of organic acids is probably 

 quite rapid, and consequently these soils, as indicated by the data, may contain 

 permanent active acidity as well as permanent negative acidity." 



