HUMUS. 55 



air all trace of structure is destroyed by the leaves being 

 passed through the bodies of worms, caterpillars, &c. He 

 states that fungi aid greatly in disseminating humus (say from 

 a dead root) through the soil. In black earth the humic acid 

 is almost exclusively in combination with lime. 



According to Eggertz* the organic substance obtained by 

 extracting a soil with alkalis, filtering, and precipitating the 

 filtrate with an acid, is soluble in water, alkalis, ammonium 

 carbonate, oxalate, or phosphate, and in sodium or potassium 

 carbonate, but insoluble in acids, ammonium chloride, sulphate, 

 and nitrate, and in potassium sulphate and phosphate. The 

 calcium compound is insoluble in water and alkalis. The 

 potassium or sodium compounds are decomposed by most 

 acids, but not by carbonic or boric acid. The substance is 

 very complex and contains, apparently as essential constituents, 

 small quantities of phosphorus, sulphur, and iron, in addition 

 to carbon, hydrogen, oxygen, and nitrogen. 



Thirteen analyses gave numbers between the following 

 limits : 



Carbon ... ... 4O8 to 56-2% 



Hydrogen ... ... 4*3 6'6 



Oxygen ... ... 25'1 38'0 



Nitrogen ... ... 2-6 6'4 



Silica ... ... -37 10-5 



Phosphorus ... ... -15 - 7'6 



Sulphur ... ... -55- 2-1 



Alumina and ferric oxide -38 3-9 



The mineral matters associated with or included in the 

 "humus" become soluble as the organic matter undergoes 

 oxidation and yield an important quantity of plant food. 



A number of analyses of humus were published by Snyder,f 

 but they throw little light upon its constitution. The average 

 composition of the ash of precipitated humus was as follows : 

 Potash ... ... 7-5% 



Soda ... ... 8-1 



Lime ... ... - 1 



Magnesia ... ... '3 



Bied. Cent. 18, 75; J. S.C.I. 1889, 293. t Journ. Anier. Chem. Soc. 1897, 738. 



