Proceedings of Seventeenth Normal Institute 141 



Let us see why. In the case of roch derived soils which are at 

 present strongly acid, or rather of high lime requirement, we 

 find the leachings to be always alkaline. Why is this the case? 

 When the soil waters leach from soil they are impregnated to a 

 greater or less degree with a gaseous substance. Water so im- 

 pregnated not only will not permit of the acid-acting soil material 

 extracting lime from its solution, but it will even make the soil 

 more acid by removing additional bases. This base removing proc- 

 ess accounts for the major portion of the soil acidity or lime 

 requirement. It is analogous to the action of sulphuric acid 

 upon tri-calcium phosphate, by which process the acid takes away 

 a part of the lime and leaves a salt which is lime-hungry and 

 anxious to recover and re-unite with its lime of which it was 

 robbed. So also we have in the soil acid salts, principally silicates 

 which have lost part of their lime, and also other bases. Because 

 of the loss of bases the soil has an affinity for lime which serves 

 to replace them. Probably this illustration will serve to clearly 

 show the case in point. In the laboratory we took an acid soil, 

 one which decomposes a considerable amount of lime. A solution 

 of this soil in distilled water contained neither acid nor alkali. It 

 was then treated with carbonated water and filtered, a process 

 comparable to leaching under field conditions. The filtrate of 

 carbonated water from this acid soil was decidedly alkaline. The 

 filtrate secured this alkaline material from an acid soil, and by so 

 doing the acid soil became still more acid. This was shown 

 quantitatively by determining the lime requirement of a soil, or 

 the extent of its ability to combine with CaCOg, both before and 

 after leaching. The increase in the lime requirement of the soil 

 after leaching was almost exactly identical to the amount of bases 

 leached out. Furthermore, in sections where soils are notoriously 

 acid, our surface waters, as well as our underground waters, are 

 always alkaline, except in such cases as water flowing from 

 swamps, or from some isolated regions where minerals capable of 

 forming soluble acids are to be found. 



In rock-derived soils we know acidity attributable to organic 

 sources to be negligible in most cases, and we know that with 

 increasing amount of clay in soil we have increasing acidity. It 

 is, therefore, apparent that our acidity, or need of lime as a soil 



