402 



Univi rsity of California Publications in Agricultural Sciences [Vol.3 



light colored or nearly colorless humus solutions. But when the ali- 

 quots were ignited, after evaporation, there was a very noticeable 

 blackening and charring of the residue, together with a considerable 



Loss on 

 Ignition 



KiO 



Humus 



MgO 

 CaO 



10 11 12 13 17 18 21 20 Soils 



Fio-. 17. Graph showing the loss on ignition, the amount of humus, and 



the percentages of calcium, magnesium, and potassium in the nine samples of 

 San Joaquin sandy loam. 



loss in weight. This phenomenon, in the light of the work of Gortner, 27 

 shows that these soils have a ' ' humus ' ' content above that which they 

 might be supposed to have, because of the almost complete absence of 



"Soil Science, vol. 2 (1916), pp. 395-442. 



