Dec. 17, 1917 
Soil Acidity and the Hydrolytic Ratio in Soils 
667 
In Table VII is shown the excess of acid-soluble iron oxid and alu¬ 
minium oxid in the acid soils over the amount required to satisfy the 
ratio Ca 0 :Fe 2 0 3 +Al 2 0 3 :: 1:1.3, and the ratios between the calcium oxid 
required by indirect titration and this excess of iron oxid plus aluminium 
oxid. 
Table VII .—Excess (in pounds ) of iron oxid plus aluminium oxid over ratio 1 to r.j 
and ratios of calcium oxid required by titration to excess of iron oxid plus aluminium 
oxid 
laboratory No. 
2 . . 
6 .. 
7- ■ 
9. 
10, 
13 
14 
16 
Excess of iron oxid plus 
aluminium oxid. 
Laboratory No. 
Excess of iron oxid plus 
aluminium oxid. 
Over 1 : 1 . 3 . 
Ratio of 
calcium 
oxid by 
titration. 
Over 1 : 1 . 3 . 
Ratio of 
calcium 
oxid by 
titration. 
Pounds. 
Pounds. 
2,790 
i-37 
*7 . 
I, 122 
x. 19 
4,485 
1 . 38 
20 . 
4, OS 2 
I- 45 
1,928 
1. 21 
21 .. 
2,758 
1 . 45 
1 , 943 
1, 22 
22 . 
690 
1. 05 
4,166 
i- 33 
23 . 
3,364 
1. 56 
3j I 49 
3i 
24 . 
1,449 
1.25 
7 . coo 
1. 20 
■l. 
1, 070 
I* 41 
o> oyy 
2, 922 
i- 33 
28. 
5 7 / 
879 
* *T* 
i* 33 
It may be seen from Table VI that the “lime requirement” as deter¬ 
mined from the neutral-soil ratio and by indirect titration closely agree, 
causing the neutral ratio for all the acid soils to approximate 1:1.3 also, 
as shown by Table VII, when the lime required to neutralize the acid 
soils is compared to the excess of iron oxid plus aluminium over the 
ratio 1 :i.3, these ratios closely approach the same figure. The relation¬ 
ship between acid-soluble calcium and iron and aluminium compounds 
in these soils and the soil reaction is clearly shown, and it is also evident 
that we are dealing with equilibrium conditions. 
Experiment iii. —This experiment was performed to determine, if 
possible, the nature of the equilibrium—that is, whether physical or 
chemical. Soil 23 was chosen, the procedure being similar to that 
used in determining “lime requirements” by the indirect-titration 
method, except that after standing, the several portions were filtered, 
the soil washed with cold distilled water, and the filtrates titrated with 
an acid solution equivalent to the limewater solution used, with phe- 
nolphthalein as indicator. The experiment was performed in two ways: 
(1) By keeping the quantities of soil constant and varying the quantities 
of calcium oxid in contact with the soil, and (2) by varying the quan¬ 
tities of soil but keeping those of calcium oxid constant. The concen¬ 
trations change, however, when the soil begins to take up lime. The 
results are given in Table VIII. 
