ORGANIC MATTERS OF THE SOIL. 229 
moist soil, and in every soil after rain, crenic acid is pro- 
duced, so that the action or effects of these substances are 
alternately manifested.” 
The Humus Bodies Artificially Produced. — When 
sugar, cellulose, starch, or gum, is boiled with strong hy- 
drochloric acid or a strong solution of potash, brown or 
black bodies result which 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 vigorous oxidizing 
agent), crenic and apocrenic acids are formed. The pro- 
duction of these bodies by such artificial means gives in- 
teresting confirmation of the reality of their existence, 
and demonstrates the correctness of the views which have 
been advance:l 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 
opportunity to understand. 
The Condition 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- 
tural 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 
