THE COMPOSITION OF THE SOIL 143 



sembling humus. He also found indications of hydroxy- 

 methylfurfuraldehyde in a dunged soil and in rotting straw in 

 which humus was being produced. He suggests, therefore, 

 that the formation of humus in the soil proceeds in two 

 stages : 



Carbohydrate (Cellulose, etc.) ( + Aminoacid)-> 



Hydroxymethylfurfuraldehyde. 

 Hydroxymethylfurfuraldehyde + amino acid -> humus + 



furfural + CO 2 by condensation. 



Eller and Koch, 1 on the other hand, suppose that humus 

 is formed by the oxidation of quinones which arise by the 

 elimination of water from hexoses : 



C 6 H I2 6 = 4 H 2 + C,H 4 O f 



Beijerinck (17) has already found quinone among the products 

 of certain soil organisms working in culture solution. 



As to the constitution of humus little is known. Sven 

 Oden of Upsala (218*2) has adduced evidence from the con- 

 ductivity of the solution in ammonia that the alcohol insoluble 

 portion is a true acid, as was supposed by the older chemists 

 and by Tacke (278). Ehrenberg and Bahr (93</) also agree 

 with this view : they show that it neutralises sodium hydroxide, 

 the point of neutralisation being sharply indicated by con- 

 ductivity measurements. On dilution the sodium compound 

 behaves as a salt or a tri- or tetra-basic acid. Further evi- 

 dence of true acidic nature is afforded by the fact that the 

 alkaline solution behaves as a true solution, and shows none 

 of the properties of colloids (Oden, 218$). There is, however, 

 another view (see p. in) that the acidic properties are the 

 result of the colloidal condition and not of a true acid con- 

 stitution, but it is improbable that this is a complete explana- 

 tion of the phenomena. 



For a long time the humus soluble in alkalis was supposed 

 to play a great part in determining fertility: Grandeau (i \2d) 

 and Hilgard (133) especially considered it to be the most 



1 Wilhelm Eller and Kate Koch, Ber., 1920, 53 B, 1469-1476. 



