TEE OBGAJSriG MATTER OF THE SOIL 146 



500 cubic centimeter flask, which is filled to the mark 

 with 4 per cent ammonia. Digestion is allowed to pro- 

 ceed for twenty-four hours, with frequent shakings, and 

 and an aliquot portion of the supernatent liquid is taken 

 for analysis. This method with its modifications is 

 practically the only one that we have for tlie estimation 

 of soil humus. It is based on the fact that when a 

 soil is lacking in active basic material, the humous 

 matter may be extracted with ammonia. A modification 

 of this method may be used as a test for soil acidity, 

 as any soil of humid regions allowing the extraction of 

 humus by ammonia alone must lack basic materials. 



The composition of the ash constituents of the matiere 

 noire is given by Snyder ^ as follows, the data being the 

 average of eight analyses : — 



The Ash froh the Humus of Minnesota Prairie Soils 



Percentage 



Insoluble 61.97 



FeaOs 3.12 



AI2O3 . 3.48 



K2O 7.50 



NaaO 8,13 



CaO 09 



MgO .36 



P2O5 12.37 



SO3 98 



CO2 1.64 



The relatively high percentage of phosphoric acid is 

 immediately noticeable in this analysis. This indicates 



1 Snyder, Harry. Soils. Minnesota Agr. Exp. Sta., Bui. 41, 

 p. 30. 1895. 



