

THE COMPOSITION OF THE SOIL 



141 



Schreiner and Shorey (250) have attempted a resolution 

 of the " humic acid " and of the " crenic acid " (the part not 

 precipitated by HC1) and have obtained the following sub- 

 stances from the alkaline or alcoholic extract : 



Substances Precipitated by Acids (the so-called 

 Humic and Ulmic Acids). 



Substances not Precipitated by Acids (the so- 

 called Crenic and Apocrenic Acids). 



Resin acids. 



Resin esters. 



Glycerides. 



Paraffinic acid, C 24 H 48 O 2 , m.pt. 45-48, 

 probably identical with the acid 

 formed on treating paraffin with fum- 

 ing nitric acid. 



Lignocericacid, C 24 H 48 O 2 , m.pt. 8o-8i, 

 isomeric with above. 



Agroceric acid, C 21 H 42 O 3 , m.pt. 72-^, 

 a hydroxy fatty acid. 



Agrosterol, C 26 H 44 O, m.pt. 237. 



Phytosterol, C^H^O . H 2 O, m.pt. 135. 

 Both of the cholesterol group. 



Dihydroxystearic acid, C 18 H 36 O 4 ,.m.pt. 



g8 -g9, identical with the acid formed 



on oxidising elaidic acid. 

 a-Picoline y-carboxylic acid, C 7 H 7 O 2 N, 



m.pt. 239, identical with the acid 



formed on heating uvitonic acid to 



274. 



Xanthine, C 5 H 4 O 2 N 4 . 

 Hypoxanthine, C 5 H 4 ON 4 . 

 Cytosine, C 4 H 5 ON 3 . H 2 O. 

 Histidine, C 6 H 9 O 2 N 3 . . 

 Arginine, C 6 H 14 O 2 N 4 . 

 A pentosan. 



None of these, however, is the black substance which is 

 the real characteristic of " humus," and until recently this had 

 eluded investigation and was vaguely described as a " melanoid 

 body ". It can be split up by solvents into the following sub- 

 stances which are no doubt further resolvable : 



Insoluble in NH 4 HO 



I 



Soluble in acids 

 {Mulder's apocrenic acid) 



Pptd. by acids 

 Humus 



Humin 



Insoluble in alcohol Soluble in alcohol 

 Humic acid Hymatomelanic acid 1 



(see Schreiner and Shorey) 



Insoluble in pyridine Soluble in pyridine 



The substances are probably related : at any rate they occur 

 together. There is good evidence that soil humus is formed 

 mainly from cellulose : no great amount is produced from 

 protein. Addition to the soil of wool, silk waste, flour, and 

 lucerne meal causes no gain, but on the contrary loss of 



1 For Hoppe-Seyler's hymatomelanic and fulvic acids see Odn, 2190. 



