THE CONSTITUTION OF THE SOIL 



71 



by boiling sugar with hydrochloric acid, on the singularly inadequate 

 ground that the product thus obtained is also a brown colloid. Numerous 

 analyses have been made both of the natural and the synthetic " humic 

 acid " some of which are given in Table XXXI.' 



Table XXXI. — Analyses of the Organic Material Extracted by Alkalis from 

 Soil (often called Humus, Soluble Humus, Active Humus, MATikRB Noire, 



ETC.). 



These results are in accordance with the general fact brought out 

 by the field observations, that under similar conditions the humus 

 mixture is tolerably constant, but it is quite clear that each set of soils 

 gives up a different lot of substances to alkalis. Indeed simple varia- 

 tions in the time or the method of extraction cause differences in the 

 results even from the same soil.^ 



The fact that humus is not a definite compound but a complex in- 

 definite colloid was established by van Bemmelen in a remarkable paper 



' Many partial analyses have been made. Cameron and Breazeale (66) in nineteen 

 samples obtained percentages of carbon varying &om 33-3 to 50"i, whilst Hilgard (133) found 

 the nitrogen content to be : — 



Percentage of 



Humic Acid in 



the Soil. 



Percentage of Nitrogen in the 

 Humic Acid. 



Soils of the arid regions (decomposition 

 rapid) 



Soil of the sub-irrigated arid regions . 



„ humid regions (decomposition 

 slow) ' . 



0"20 to 3'0 

 0-36 „ 2'o 



I'O „ io"o 



87 to 22-0 (average i5"2) 

 5-4 „ 10-8 ( „ 8-4) 



17 It r° ( 



4-2) 



Westermann (302) has analysed humus from the Danish moors, and Gully (114) has studied 

 humus from South Bavarian moors. Many of the older analyses have been collected by 

 WoUny (319)- 



'This is shown by the analyses of Miklauz (Zeit.f. Moorkultur u. Torfverwertung, 

 igo8, 285) and Mayer. Sostegni (268) in 1886 had shown that humus is readily fractionated. 



