EXPERIMENT STATION BULLETINS. 867 



The freezing point metliod gives mucli higher lime requirement than 

 the Veitch method. It appears that the former method probably gives 

 the true maximum lime requirement of soils. By true maximum lime 

 requirement is meant the total amount of lime required to neutralize any 

 soluble acids and acid salts of soils and to satisfy their absorption- 

 adsorption properties for lime. 



All the mineral soils tested gave an absorption curve, indicating 

 probably that they did not contain a soluble acid or acid salt. 



The absorption curve of the mineral soils signifies that the Ca(0H)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. A critical consideration of the soil mass as well 

 as many experimental evidences seem to indicate that these solid sub- 

 stances, in the case of the mineral soils, consist mainly of unsaturated 

 silicic acid, silica, acid alumino-silicates, and perhaps insoluble organic 

 matter, probably in the colloidal, hydrated form. 



The absorption curve also indicates that there is no basic exchange 

 in soils, when a hydrate is employed, until the soil is satisfied or satur- 

 ated with the base. 



Only a few peats were tested and most of them gave an acid curve, 

 indicating probably that most of them contained free acids. 



The same kind of soils took up Ca(OH)o, KOH, NaOH, and NH^OH 

 in non-chemically equivalent amounts. As a very general rule each soil 

 tended to show a specific reactivity for these different hydrates. This 

 unequal absorption does not appear to be against the value of the 

 freezing point method. 



When a soil was satisfied with 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 was only partly satisfied with 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. The results plotted into an acid curve. 



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 test showed that it was very nearly neutral. The sediment, how- 

 ever, gave an acid curve, signifying that it contained a considerable 

 amount of acid. It turned the blue litmus paper red. When this sedi- 

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

 be obtained, showing that the acid was washed away. 



All soluble salts increased the lime requirement of soils, but the magni- 

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

 acid phosphate salts. All of the former salts employed augmented the 

 lime absorption of any one soil to the same degree. The same was true 

 of all the latter salts. The increase, however, in both cases was only 

 temporary, as after washing with water the soils possessed the same lime 



