Absorption by Soils of Potassium. 



173 



in the volume of the filtrate the curve rises and almost reaches the 

 upper boundary of the figure, which line represents the original strength 

 of the solution. At this point the removal of the absorbed potassium 

 is begun by leaching with pure distilled water. It should be noted 

 that at this point the curve falls rapidly to practically a straight line. 



Figure 19 gives the results expressed in terms of the soil, the abscissae 

 being the volume of the solution or water percolated through the soil, 

 and the ordinates the amount of potassium absorbed, expressed in parts 

 per million of the air-dry soil. While it is possible, and indeed quite 

 probable that complete equilibrium was not reached, it is apparent 



- * 



. . 



Liters of solution 



300 



a 



0.05 



0.10 0.15 



Solution 



0.20 



0.25 O30 



->)* Liters Jt- 



FIG. 19. 



0.35 



040 0.45 



Water 



0.50 



0-55 



-H 



that the soil is rapidly approaching a saturated condition after having 

 absorbed 230 parts per 1,000,000 of potassium as a result of the perco- 

 lation of 250 c.c. of the salt solution. The part of the curve repre- 

 senting the removal of the absorbed salt by leaching with distilled 

 water is a straight line, showing the uniformity with which the absorbed 

 material is removed. This removal of the absorbed potassium was 

 accomplished by filling the filter chamber with distilled water and 

 continuing the percolation at the same rapid rate as was used with the 

 solution of potassium salt. 



