THE EXCHANGE OF IONS 
groups themselves formed a series 
ranging by intervals of 120 NX 
io~^ from 120 to 480 N X io~^ 
In addition to the twenty salt 
solutions, there was a check cul- 
ture in distilled water. 
In figure I the daily concen- 
tration of each member of the 
four groups of solutions is shown 
for a total experimental period 
of 16 days. On the horizontal 
axis the unit is one day. The 
original total salt concentration 
of any solution in terms of gram 
equivalents per million liters is 
given at the left on the perpen- 
dicular axis. An increase in con- 
centration of a solution during 
the experiment is therefore indi- 
cated by an upward trend of the 
curves; a decrease by the con- 
verse. The changes in concen- 
tration of the five solutions be- 
longing to each group are of 
course indicated by a family of 
curves departing from the same 
point on the axis of ordinates. 
The course of the concentration 
changes taking place in the dis- 
tilled water check is indicated by 
a curve starting at o on the axis 
of ordinates and covering about 
12 days prior to the onset of 
changes attributed to exhaustion 
of the plants. 
In the 120 N X io~^ group of 
solutions all members seemed to 
gain ionsduring the first twodays. 
This apparent loss of electrolytes 
/ 2 3 4-5 6 7 8 9 10 II 12 13 14- IS 16 
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Fig. I . Curves showing the change in 
concentration of the Ca(N03)2 and 
KNO3 solutions used in experiment i. 
