Oct. 30 , I923 
Soil Reaction in Relation to Calcium Adsorption 
89 
CALCIUM HYDROXID AND WATER FOR DILUTION 
o A 
The calcium hydroxid solution was made by adding distilled water to 
an excess of calcium oxid and allowing to settle. The titration value and 
calcium in a measured portion had to be determined frequently, as it was 
found that the concentration would change slightly on standing in con¬ 
tact with an excess of solid Ca(OH) 2 . For some of the work, solutions of 
definite Ca(OH) 2 concentrations were made. To make these was time- 
consuming; furthermore, it was impossible in practice to maintain a con¬ 
stant concentration for any considerable period of time. A more satis¬ 
factory procedure was 
to use a saturated M 
Ca(OH) 2 solution of 
known strength, and 
to adjust the relative 
proportions of soil, 
Ca(OH) 2 solution and 
water in such a way 
that a definite number 
of cc. of the Ca(OH) 2 
solution would repre¬ 
sent the number of 
milligrams of calcium 
desired per 10 grams 
of soil. 
When ordinary dis¬ 
tilled water was used, 
it was purified by bub¬ 
bling air free of C 0 2 
through it for about 
five hours. At the 
end of this time 100 cc. would give a distinct color with 1 drop of 0.05 N 
NaOH, using phenolphthalein as an indicator. For most of the work 
water made in a conductivity still was used. 
D 
Fig. 3.—Apparatus for shaking the support for the electrode vessels. 
Red D is fastened in an ordinary laboratory clamp holder. The radius 
of the circle described by the crank pin C can be changed by adjusting 
the screw at B. By this arrangement and by altering the speed of 
the motor, the electrode vessels can be subjected to any desired degree 
of shaking. 
RELATIVE AMOUNTS OF SOIL, LIQUID, AND CALCIUM 
On the basis of some preliminary work, and also the work of Sharp and 
Hoagland (41), Plummer (37), and others, it was decided to use soil and 
liquid in a ratio of 1 :io. The amount of soil and other materials used in 
the different determinations were such that the final data are on the basis 
of 10 grams of soil. A saturated solution of Ca(OH) 2 has a normality of 
about 0.042, but for convenience in final calculations the dilutions of the 
Ca(OH) 2 solution were calculated to the basis of 0.04N, or a definite frac¬ 
tion of this normality. Five cc. of 0.04N Ca(OH) 2 solution contain 4 
mgm. of calcium, or the equivalent of 10 mgm. CaC 0 3 . This gives a ratio 
of 1 :i,ooo when 10 grams of soil are used, or, figuring the weight of soil 7 
inches deep at 2,000,000 pounds, the equivalent of 1 ton per acre. Ac¬ 
cordingly each cc. of 0.04N Ca(OH) 2 represents 400 pounds of CaC 0 3 per 
acre. In a few of the experiments, where calcium hydroxid solutions of 
definite concentrations were used, there is a variation from this ratio. In 
such instances the exact amount of calcium added per 10 grams of soil is 
given. 
