662 
Journal of A gricultural Research voi. xxvn, no. 9 
confused by many authors who have held the view that the soil absorbs 
substances from solution and who have not been clear that such absorp¬ 
tion constituted but one part of an exchange reaction. The results of 
experiments which show quantitatively the extent of such exchange 
reactions are not numerous, probably because many investigators do 
not make quantitative determinations of sodium in the course of their 
experiments. The early experiments of Way ( 21 , p. 332,334) showed 
that when a soil which contained only traces of water-soluble calcium 
was leached with solutions of potassium and sodium salts the percolate 
was practically free from potassium or sodium but instead contained 
calcium in abundance together with the acid radical contained in the 
original leaching solution. 
More recently Gedroiz (8) has shown that a soil which would give up 
to 20 consecutive digestions with water (ratio of 5:1) only 0.176 per 
cent of CaO gave from similar treatment with a normal solution of sodium 
chlorid 1.244 P er cen t CaO. In a later paper the same author (9) de¬ 
scribes an experiment in which a sample of soil was first digested 
repeatedly with solutions of sodium chlorid until equilibrium was estab¬ 
lished between the solution and the soil. The soil was then washed, 
dialyzed, and dried. The treated soil was then analyzed by digestion 
with 10 per cent hydrochloric acid and its calcium content compared 
with that of the original untreated sample. The original sample con¬ 
tained 1.36 per cent CaO extractable by 10 per cent hydrochloric acid, 
while the sample that had been brought into equilibrium with a normal 
solution "of sodium contained only 0.36 per cent CaO extractable in the 
same way. This result indicates that the absorption by the soil of a cer¬ 
tain quantity of sodium from the solution of sodium chlorid had resulted in 
releasing into solution 1 gm. of CaO or 0.715 gm. calcium from 100 
gm. of soil. 
The quantity of sodium that was absorbed by the soil during the 
treatment described was also determined by analyzing samples before 
and after treatment. These analyses showed that the original soil con¬ 
tained 0.05 per cent Na^, while after treatment with the sodium-chlorid 
solution it contained 1.42 per cent. This is equivalent to 1.016 gm. 
of sodium absorbed by 100 gm. of soil. 
The absorption of this quantity of sodium was accompanied by the 
release of other bases than calcium from combination with the soil. 
Two of these, magnesium and potassium, were identified by the analyses. 
It was found that the absorption of sodium had caused the release of 
0.12 per cent of MgO and of 0.03 per cent of K 2 0 . The analytical results 
of this experiment are summarized in Table XXII. 
Table XXII .—Percentages of combined (not water soluble) bases in a sample of Russian 
black earth in its original condition and after being brought into equilibrium with a 
normal solution of sodium chlorid a 
Sample. 
Original soil 
Treated soil. 
Replaced... 
Absorbed... 
Constituents soluble in xo per cent hydrochloric add. 
in percentage of dry soil. 
CaO. 
MgO. 
KisO. 
Na a O. 
I. 36 
O. 87 
O. 52 
0.05 
•36 
• 75 
.49 
I. 43 
I. OO 
. 12 
•03 
r *'37 
• From Gedroiz. 
