868 STATE BOARD OF AGRICULTURE. 



requiremeut as before treatment. Before wushiug, the soils gave the acid 

 curve with all the salts, but after washiug they all yielded the absorption 

 curve, proving that the substance which caused an increase in the lime 

 requirement and produced the acid curve, was washed away. 



The same phenomenon was observed in the case of the salt solutions, 

 as in the acids, namely, when a soil which showed a high lime require- 

 ment was treated with an excess of salt solution, the supernatant liquid 

 failed to give an acid curve but the sediment did, but when the sediment 

 was washed with water, then it no longer gave the acid curve, but the 

 absorption curve. These phenomena are very remarkable and exceedingly 

 significant. 



Since no mineral soil out of a great number tested 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 Avith neutral salts, 

 or acid and acid salts, were carried away by washing and the soils then 

 gave an absorption curve, the conclusion seems to be 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 per- 

 manent. The acidity or lime requirement of soils, therefore, 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, how^ever, 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 nega- 

 tive acidity. 



