230 HOW CROPS FEED. 
which are acted upon by the carbonates of potash, soda, 
and lime, that become ingredients of the soil by the 
solution of rocks, or by carbonate of ammonia brought 
down from the atmosphere or produced by decay of ni- 
trogenous matters, acquire solubility, and are, in fact, 
acids; and these portions are acids in combinaticn (salts), 
and not in the free state. 
The Salts of the Humus Acids that may exist in the 
soil, viz., the ulmates, humates, apocrenates, and crenates 
of potash, soda, ammonia, lime, magnesia, iron, manga- 
nese, and alumina, require notice. 
The ulmates and humates agree closely in their charac- 
ters so far as is known. 
The ulmates and humates of the alkalies (potash, soda, 
and ammonia) are freely soluble in water. They are formed 
when the alkalies or their carbonates come in contact Ist, 
with the ulmic and humie acids themselves; 2d, with the 
ulmates and humates of lime, magnesia, iron, and manga- 
nese; and 3d, by the ection of the alkalies and their car- 
bonates on humin and ulmin. Their solutions are yellow 
or brown. 
The wimates and humates of lime, magnesia, iron, man- 
ganese, and alumina, are insoluble, cr but very slightly 
soluble in water. 
From ordinary soils where these earths and oxides pre- 
dominate, water removes but traces of humates and 
ulmates. 
From peat, garden earth, and leafmould, which contain 
excess of the humic and ulmic acids, and carbonate of 
ammonia resulting from the decay of nitrogenous matters, 
water extracts a perceptible amount of these acids render- 
ed soluble by the alkali. 
There appear to exist double salis of humic acid and of 
ulmic acid, i. c., salts containing the acid combined with two 
or more bases. By adding solutions of compounds (e. g., 
sulphates) of lime, magnesia, iron, manganese, and alumina 
