Dec. 17, 1917 
Soil Acidity and the Hydrolytic Ratio in Soils 
665 
Table V. —Quantity of acid-soluble silica (Si 0 2 ) in 2,000,000 pounds of the soils and 
also the “lime requirement** of the acid soils by Veitch method 
Add soils. 
Alkaline soils. 
2. 
6 . 
7 - 
9 - 
10 
13 
14 
16, 
i 7 ' 
20. 
21. 
22. 
2 3 - 
24. 
27. 
28. 
Laboratory No. 
SiO 2. 
Lime re¬ 
quirement. 
Pounds . 
Pounds . 
1,020 
960 
670 
620 
520 
730 
960 
S40 
2, 520 
780 
640 
I, no 
640 
I, 020 
590 
730 
I, 560 
1,320 
1,440 
1,440 
1,440 
1,440 
I, 560 
1,440 
3,600 
I, 200 
1,080 
1,56° 
1,440 
I, 800 
1,320 
I, 560 
3 - 
4 - 
5 - 
8 . 
11 
12 
15 
18 
19 
25 
26 
29 
Laboratory No. 
SiO 2 . 
Pounds . 
h 57 ° 
T , 33 <> 
1,230 
I. 430 
5 TJ W 
1,380 
2, 280 
1,490 
I, OIO 
1,370 
1,460 
3 > 48 o 
2, 060 
850 
From the data given in Tables I and II it is evident that the relation¬ 
ship between the acid-soluble calcium and iron and aluminium may 
control the soil reaction. The question is, then, under what conditions 
can this phenomenon be produced. It is well known that many calcium 
salts hydrolyze in solution giving an excess of base, and reacting alkaline 
to litmus indicator, and that iron and aluminium salts generally produce 
acid solutions under similar conditions. The reaction of a solution con¬ 
taining a mixture of a salt that hydrolyzes and gives an excess of hydrion 
with a salt that produces an excess of hydroxidion on hydrolyzing depends 
upon the concentration and degree of hydrolysis of each salt in the 
presence of the other when equilibrium is established. The term “hydro¬ 
lytic ratio” is used here to express this relationship. In other words, 
if the acid exceeds the alkali by chemical equivalents, the solution will 
react acid, and an alkaline solution results on reversing the conditions, 
while a certain hydrolytic ratio gives a neutral solution. 
Results obtained from the analytical determinations with the solubility 
method and the theory of hydrolysis give a basis for the following hypo¬ 
thesis : that the reaction of these soils is probably determined chiefly by 
the hydrolytic ratio between salts of the alkaline earth elements on the 
one hand and salts of iron and aluminium on the other when these 
compounds are in equilibrium. From this standpoint any hydrolyzable 
salt in a soil or added to a soil, or any salt added to a soil that causes the 
formation of a hydrolyzable salt, may influence the soil reaction. In the 
following pages other data are given to support the above hypothesis. 
Experiment ii. —The quantity of lime required to neutralize these 
soils was determined by indirect titration with limewater in the following 
