HUMUS 71 



Ammonia compounds." Mulder was one of the 

 first in 1849 to attempt really to describe it chemic- 

 ally. He explained that it consisted of seven organic 

 compounds closely related to each other namely, 

 Crenic acid, Apocrenic acid, Geic acid, Humic acid, 

 Humin, Ulmic acid, and Ulmin. Modern workers 

 would recognize the problem as being one of far 

 greater complexity, but fortunately the early stages 

 of any investigation into it are easily carried 

 out and understood. Few terms have to be used, 

 and to them it is possible to give a well-defined 

 meaning. 



Humus, according to the modern views held as to 

 its structure,* can be divided somewhat artificially, 

 perhaps, into four chief groups of substance Crenic 

 acid, soluble Humic acid, insoluble Humic acid, and 

 Humin. If a sample of humus is taken and ex- 

 tracted with alkali, a portion of it, known as Humin, 

 is insoluble. On treating the soluble alkaline liquid 

 with acid a precipitate is formed, but Crenic acid 

 derived from the humus remains in the liquid. If 

 the precipitate is boiled with alcohol, a portion of it 

 is soluble, soluble Humic acid, and a portion in- 

 soluble, insoluble Humic acid. To some extent 

 these bodies are not present in the original humus, 

 but they represent groups of bodies that are present, 

 and as the classification is very valuable if one 

 wishes to get as clear an understanding as possible 



* The latter portion of this chapter is based on the paper by 

 Professor Bottomley in the Biochemical Journal, June, 1915, 

 " The Formation of Humic Bodies from Organic Substances." 

 Those wishing for fuller details should consult the original 

 paper. 



