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A BULLETIN 6, U. S. DEPARTMENT OF AGRICULTURE. 
CHANGE FROM ACIDITY TO ALKALINITY. 
The reason for this change from acidity to alkalinity lies primarily 
in the chemical composition of the leaves. From the beginning | 
they are heavily charged with lime, as the following determinations 
in Table IT will show:* 
TaBLe I1.—Percentage of lime in freshly fallen leaves, in terms of calcium car- 
bonate. or ground limestone. 
Se Percentage aba we ' Percenta 
a AG eeeeee jes ind of leaves. ea cS 
Kind ef leaves. AE Kind ofleaves of lime. 
Wiliiie naka se. 2s eee 112)|| Susarmaples_- = ue ss eae eee 4.56 
Recor) es es ee eee Be 3-08 |) Colip tree 5.06 
SHUTS PINE TT GS ee Se ee ee S. SEU Virginia pines. <= Se eee 16 
Soils containing such high percentages of lime as these leaves 
would be markedly alkaline, yet the leaves, as shown by the table on 
page 2, are strongly acid. It is evident from a consideration of both 
facts that the lime existing in the fresh leaves has gone into combina- 
tion with their acid substances to the fuli extent of its ability to neu- 
tralize them, and that the acidity recorded on page 2 represents the 
acid substances in the leaves in excess of the amount already neutral- 
ized by the lime. | 
As the decomposition of the leaves progresses these excess acid 
substances are leached out or disorganized. the lime itself is released 
from its combinations, and a stage is reached where the lime is more 
than sufficient in amount to neutralize the remaining acidity. The 
mass has become an alkaline leaf mold. This change from acidity to 
alkalinity is often hastened by the development through bacteria of 
ammonia or other substances having an alkaline reaction. 
The rapidity with which different kinds of leaves pass from the 
acid to the alkaline stage varies exceedingly. Leaves of silver maple 
in some tests have rotted so rapidly as to reach the alkaline state 
within ayear. Red-oak jeaves remain acid for several years, and pine 
leaves for many years. 
ACIDITY OF GREEN MANURES. 
Acidity determinations of several of the plants that are commonly 
plowed under for green manure give the following results, expressed 
m the weight of ground limestone that would be required per acre to 
neutralize a compact layer 6 inches in thickness. 
1 These lime determinations were made by Mr. J. F. Breazeale. of the Bureau of Chem- 
istry, from duplicates of the same samples from which the acidity determinations on 
page 2 were made. 
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