78 THE SPIRIT OF THE SOIL 



chloric acid; (3) an alkali-soluble substance giving 

 the typical flocculent precipitate of Humic acid when 

 treated with Hydrochloric acid; and (4) a black 

 residue insoluble in water and alkalies, and giving 

 the typical Humin reactions. Curious differences 

 were found to occur when Dextrose and Laevulose 

 were similarly treated, but these are points of detail 

 that hardly concern us here. The points to which 

 I would call attention are (i) that the heat -formed 

 Humic acids differ from the acid-formed Humic acids, 

 in that on being dried in a water-bath at 100 C. 

 they are no longer soluble in dilute alkali solution, 

 but are only rendered soluble on fusion with 

 caustic potash or soda; (2) that by heating or 

 by treating with acid the change to Humin is 

 via Humic acid; and (3) that in both cases the 

 general effect of the treatment is, as in Nature, to 

 take the elements of water out of the molecule of 

 carbohydrate. 



Plant tissues consist chiefly of carbohydrates and 

 proteins. The latter are of varied composition, but 

 consist of Carbon, Hydrogen, Oxygen, and Nitrogen 

 in combination, and the Hydrogen and Oxygen may 

 or may not be in the proportions necessary to form 

 water. Similar tests to those made on sugar have 

 been carried out with the proteins, and it has been 

 found that Humic bodies are produced only in so far 

 as the proteins contain carbohydrate. For instance, 

 while a gramme of Mucin, which contains carbo- 

 hydrate, on boiling for eight hours with a 7*5 per 

 cent, solution of Hydrochloric acid, yielded 

 0*028 gramme of Humic acid, no Humic acid was 



