Apr. 15, 1918 Soil Acidity as Influenced by Green Manures 



191 



was then burned in this dish, the loss in weight counted as free and 

 combined humic acid, and the mineral residue as humus ash. 



B. — iVn equal weight of the soil was treated in exactly the same way, 

 except that the removal of the bases by washing with hydrochloric acid 

 and water was omitted. The loss on burning the alkali-soluble material 

 obtained in this manner was counted as free humic acid and the associ- 

 ated humus ash determined as in the preceding case. 



It is to be observed that if any portion of the organic matter is sol- 

 uble in either weak hydrochloric acid or water, or both, and also in 

 weak ammonia water, a loss of this fraction of the material would occur 

 with the treatment by the usual method. A, but not by method B. 

 In such case these two treatments would not give the full measure of 

 the material, free and combined with basic matter, that is capable of 

 solution in the weak alkali. 



Table XVI. — Determinations of humus and humus ash in experiment mixtures (Series 



I and II) 



a Omitted from grand average. 



