666 
Journal of Agricultural Research 
Vol. XI, No. 12 
manner: 6-10, 300-c. c. Erlenmeyer flasks were used for each soil, 1 gm. 
of air-dried soil was placed into the first flask and the quantity increased 
in the remaining flasks by increments of 1 gm. each. Fifty c. c. of distilled 
water were then added to each flask and ten c. c. of a standardized lime- 
water solution. The flasks were sealed immediately with rubber stoppers, 
shaken several times, and allowed to stand about 16 hours. End points 
were determined in two ways: (1) by means of electrical resistance, and 
(2) with phenolphthalein indicator. Resistance measurements were 
taken by removing 25 c. c. of the supematent solution with a pipette to 
a resistance cup and the readings taken with a Kohlrausch bridge. The 
highest resistance reading in the series was taken as the end point. A 
drop of indicator was then placed into each flask and the end point 
taken when the red color showed faintly. In all cases with the soils 
under discussion there was exact agreement in the end points as 
determined by the two methods. 
On considering the ratio CaO : Fe-jOgH- A 1 2 0 3 :: 1 :1.3 to be correct for 
a neutral soil, the “lime requirement” of the acid soils may be computed 
by determining the quantities of calcium oxid necessary to add to the 
calcium oxid found soluble in the soils to bring all the ratios to 1:1.3. 
Table VI contains these figures, together with the “lime requirement” 
as determined by indirect titration. The quantities of add-soluble 
calcium oxid plus the quantities of caldum oxid required to neutralize 
the soils by indirect titration are given in the fourth column, and the last 
column contains the ratios between these quantities of caldum oxid and 
the quantities of acid-soluble iron and aluminium. 
Table VI .—Lime requirement and ratios produced by neutralizing acid soils 
[Expressed as pounds per 2,000,000 pounds of soil.] 
Laboratory No. 
Calcium oxid 
required 
from neutral 
ratio. 
Calcium oxid 
required 
Acid-soluble 
calcium oxid 
+ calcium 
oxid required 
by titration 
(=X). 
Fe 2 03 + 
AlsOs 
by titration. 
X 
Pounds. 
2, 140 
Pounds. 
2, 040 
Pounds. 
6,310 
1. 32 
6.. . . . 
3 > 45 ° 
3* 240 
&630 
I * 35 
7 . 
1, 480 
x, 600 
4,700 
1. 27 
9 . 
i, 49 ° 
1,600 
2,990 
1-25 
3,210 
3 >* 4 o 
3,800 
4,670 
1. 32 
13 ... 
2,420 
2, 400 
i- 3 i 
14 . 
2,770 
2,800 
S* 45 o 
1. 29 
2,250 
2,200 
3,160 
1. 30 
17 . 
860 
940 
10,350 
1. 29 
3,120 
2,800 
4,100 
1. 40 
2,120 
1,900 
3* 680 
1. 38 
530 
660 
4,830 
1. 27 
23 . 
2,590 
2,160 
3*920 
1.44 
24. 
1, 220 
1,160 
5 * 3oo 
1. 29 
27 . 
1, 520 
1, 400 
3*440 
1. 34 
28.... 
580 
660 
4,370 
1. 30 
