EXCHANGE OF IONS 
51 
at any point is 140, indicating a total concentration of 140 N X 10 ^. 
For instance, the point marked 80 KNO3, 20 Ca(N03)2, 40 Mg(N03)2 
/\ /\ /\ /\ /\ /\ /\ /\ 
Fig. I. Residual concentration of solutions containing KNO3, CA(N03)2 and 
Mg(N03)2, at the time of maximum absorption, 
represents a solution with a total concentration of 140 N X io~^, in 
which 80/140 of the NOs" ions were derived from KNO3, 20/140 from 
Ca(N03)2 and 40/140 from Mg(N03)2. 
Inspection of the results shows in nearly all cases a preliminary 
rise in the conductance of the solutions, probably due, as we have 
suggested elsewhere, to carbon dioxide given off by the roots. After 
this preliminary rise the conductance in most cases rapidly diminishes 
until the twelfth to fifteenth day, due to the absorption of salts by 
