EFFECT OF SEEDS UPON HYDROGEN-ION CONCENTRA¬ 
TION EQUILIBRIUM IN SOLUTION 1 
By Willem Rudolfs 
Biochemist, New Jersey Agricultural Experiment Station 
INTRODUCTION 
In an earlier paper 2 it was shown 
that the hydrogen-ion concentration of 
alkaline salt solutions in which seeds 
were immersed had changed markedly 
after about 15 hours of imbibition. The 
Ph changes recorded were all in one 
direction, namely, towards the acid 
side, and appeared to be fairly definite 
for each species of seed. The conclu¬ 
sion was drawn that these reaction 
changes were directly related to ion- 
absorption by the seeds. 
The object of this paper is to show 
the rate of reaction changes and the 
existence of a definite equilibrium in 
solutions which have been in contact 
with seeds. 
EXPERIMENTAL DATA 
In view of the fact that a marked 
difference exists in the absorbing power 
of seeds of different species (seeds of 
the leguminous type show higher rates 
of absorption than seeds of the gramin¬ 
eous species 3 ), four kinds of large seeds 
were selected, as follows: Corn (Zea 
?nays ), lupine {Lupinus alhus), beans 
(Phaseolus vulgaris), and soy beans 
(Soja maxima). 
The representative salt solutions, 
mineral and organic acids, covering the 
range of acids and salt radicles, are 
given in the tables. In the case of the 
mineral and organic acids an effort was 
made to bring the different acids to a 
dilution giving approximately a reac¬ 
tion of P H 3.0. Some of the acids could 
be secured only at a nominal per cent 
and it was thought best to state the 
dilution in Ph values instead of in 
terms of normality. A large number 
of different salts were tried, but, for the 
comparison of the radicles, the repre¬ 
sentative potassium salts are selected 
and only two chlorides with other bases 
are entered in the tables. 
Fifty seeds of each species were 
placed in small bottles each containing 
100 c. c. of solution; 1.8 c. c. of this 
solution was pipetted off after definite 
time intervals, and the hydrogen-ion 
concentration of the solution was de¬ 
termined by the colorimetric method. 
The results of these determinations are 
given in the tables as the averages of at 
least two trials. In Tables I, II, and 
III the initial Ph values are compared 
with the readings at different intervals. 
The rate of reaction change is not 
the same for all salt solutions, although 
a certain equilibrium is reached in the 
solutions after the seeds have been im¬ 
mersed sufficiently long (Table I). 
Corn changed the reaction of KC1 to 
a point of equilibrium in about 15 
minutes, while 15 hours were necessary 
in the case of K 2 S0 4 . For the mineral 
and organic acids similar differences 
were observed. 
For mineral and organic acid solu¬ 
tions, considerably more time was 
necessary to reach the point of equilib¬ 
rium than for salt solutions (Tables II 
and III.) On account of the rapid in¬ 
crease in the strength of the acids 
with every increment of the P H values, 
a longer time for the reaction changes 
could be expected. Nevertheless, all 
acid solutions which had been in con¬ 
tact with the seeds after a certain 
period of time reached the same point 
of equilibrium as the salt solutions. 
The Ph values observed in oxalic 
acid and potassium chloride solutions 
(corn and beans) plotted against time 
in minutes are presented in Figure 1. 
The curves show a fairly rapid rise 
during the first few time intervals 
with a flattening out toward the point 
of equilibrium. Ordinarily the solu¬ 
tions remain at this point indefinitely, 
but slight changes can be brought 
about by an increase of temperature. 
This explains why some of the salt 
solutions show slightly different P H 
1 Received for publication Aug. 8, 1924; issued August, 1925. Paper No. 177 of the Journal series, New 
Jersey Agricultural Experiment Station, Department of Soil Chemistry and Bacteriology. 
2 Rudolfs, W. effect of salt solutions having definite osmotic concentration values upon 
absorption by seeds. Soil Sci. 11: 277-293, ihus. 1921. 
3 Rudolfs, W. effect of seeds upon hydrogen-ion concentration of solutions. Bot. Gaz. 74: 
215-220. 1922. 
Journal of Agricultural Research, 
Washington, D. C. 
( 1021 ) 
Vol. XXX, No. 11 
June 1, 1925 
Key No. N. J.-14 
