Absorption by Soils of Potassium. 



171 



screwed down over the top of the filter chamber, and the system con- 

 nected to an automobile-tire pump through the valve F. The filter 

 tube serves to hold back the fine soil particles and give a clear filtrate 

 for analysis. The apparatus is charged by putting 20 grams of the air- 

 dry soil in the brass jacket surrounding the filter tube, and pouring the 

 salt solution into the porcelain-lined chamber which surrounds the system . 



SERIES 1. 



Preliminary to the use of the soils for the 

 absorption work, samples of both the natural 

 and the finely pulverized soil were tested for 

 soluble potassium, by percolating pure distilled 

 water through them at the approximate rate of 

 200 c.c. per hour. Each successive 100 c.c. por- 

 tion of the filtrate was saved and separate deter- 

 minations made for potassium by the calorimetric 

 method used by the Bureau of Soils. 1 



Table 97 contains the results of this preliminary 

 work. The numbers in the first column indicate 

 the successive filtrates, while the second column 

 gives the concentrations of the successive portions 

 of the filtrate in parts per million of the solution. 

 The figures of the table will be used in the subse- 

 quent work, in order to correct the results for the 

 soluble potassium originally contained in the soil. 

 Although it has no direct bearing upon the ques- 

 tions under consideration, it is of interest to note 

 that the grinding of the soil in the ball mill has 

 increased its solubility in distilled water approximately ten-fold. 



TABLE 97. Water-soluble potassium in samples of Durham sandy loam soil. 



SERIES 2. 



In this series a 20-gram sample of the same natural soil as was used 

 in series 1 was percolated with 250 c.c. of a 0.005 solution of potassium 

 chloride, the flow being maintained approximately at the rate of 50 c.c. 

 in 10 minutes. The percolate was collected in fractions of 50 c.c. each, 



1 U. S. Dept. Agriculture, Bureau of Soils, Bui. 31, p. 31. 



