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.

is the alkali insoluble fraction of leonardite. (This usage of the term does not correspond exactly with the usage by other workers.)

a black humic substance that is not soluble in water