humic acid
n 1: a dark brown humic substance that is soluble in water only
at pH values greater than 2; "the half-life of humic acid
is measured in centuries"
Humin \Hu"min\, n. [L. humus the earth, ground.] (Chem.)
A bitter, brownish yellow, amorphous substance, extracted
from vegetable mold, and also produced by the action of acids
on certain sugars and carbohydrates; -- called also {humic
acid}, {ulmin}, {gein}, {ulmic} or {geic acid}, etc.
[1913 Webster]