ORGANIC MATlEns OP THE SOIL. 229 



moist soil, and in every soil after rain, crenic acid is pro- 

 dueed, so that tlie action or effects of these substances are 

 alternately manifested." 



The Iliiinjis Bodies Artificially Produced. — When 



sugar, cellulose, starch, or uuiu, is boileil with stronu; hy- 

 drochloric acid or a s rong solution of potash, brown or 

 bhick bodies result wliich have the greatest similarity with 

 the ulmin and humin, the ulmic and humic acids of peat 

 and of soils. 



By heating humus with nitric acid (a vigoi'ous oxidizing 

 agent), crenic and apocrenic acids are formed. The pro- 

 duction of tliese bodies by such artificial means gives in- 

 teresting confirmation of the reality of tlieir existence, 

 and demonstrates the correctness of the views which have 

 been advanced as to their origin. 



While the precise composition of all these substances 

 may well be a matter of doubt, and from the difficulties 

 of obtaining them in the pure state is likely to remain so, 

 their existence in the soil and their importance in agricul- 

 tural science are beyond question, as we shall shortly have 

 oj)portunity to understand. 



The Coiiditloii of these Humus Bodies in the Soil 



requires some comment. The organic substances thus 

 noticed as existing in the soil are for the most part acids, 

 but they do not exist to much extent in the free state, ex- 

 cept in bogs and morasses. A soil that is fit for agricul- 

 tuial purposes contains little or no free acid, except car- 

 bonic acid, and oftentimes gives an alkaline reaction with 

 test-papers. 



Regarding ulmic and humic acids, which, as we have 

 stated, are extracted by solution of carbonate of soda 

 from humus, it appears that they do not exhibit acid char- 

 acters before treatment with the alkali. They appear to 

 be altered by the alkali and converted through its influ- 

 ence into acids. Only those portions of these bodies 



