EXCHANGE OF IONS 
55 
greater than that from calcium nitrate alone, in the solutions with 
three anions all of the mixtures were superior to calcium nitrate alone. 
In the nitrate mixtures the most favorable solution was reduced to 
little below half its original concentration, but in the mixtures con- 
taining different anions the best solutions were reduced to about one 
\ /\ /\ /\ /\ /\ /\ /\ 
Fig. 2. Residual concentration of solutions containing KH2PO4, Ca(N03)2 
and MgS04, at the time of maximum absorption. 
tenth of their original concentration. In the nitrate series there was 
a wide range of variation in the absorption from the 15 mixtures of 
all three salts, but in the mixed anion series there was much greater 
uniformity in the final result. The least favorable mixtures did not 
depart widely from the average. Taking a maximum total absorption 
