238 PRINCIPLES OF AGRICULTURAL CHEMISTRY 



Seven additional soils gave similar results. 



(5) Ratio of Soil to Solution. Keeping the strength of solu- 

 tion constant, and increasing the weight of soil brought in con- 

 tact with it increases the total absorption, while the absorption 

 per : gram soil decreases. 



(6) Time of Contact. Peters 1 studied the time of contact, 

 using 100 grams soil to 250 cc. of solution containing 0.5889 

 gram potash : 



Time Amount absorbed gram 



% hour 0.1417 



2 hours o. 1571 



4 hours 0.1690 



8 hours 0.1860 



24 hours 0.1990 



14 days 0.2037 



Absorption of potash takes place rapidly, and is practically 

 complete in 24 hours. Similar experiments have shown that 

 phosphoric acid is absorbed more slowly. 



Solubility of Absorbed Material. Absorbed material has a low 

 solubility in water. Peters- estimated it as follows: 100 grams 

 earth was brought in contact with 250 cc. water containing 0.5888 

 gram K 2 O and after 24 hours 125 cc. was drawn off and replaced 

 with water. This process was repeated every 24 hours for 9 

 days, and each extract was subjected to analysis. The absorbed 

 potash is more soluble in water than the soil potash, but not very 

 soluble about i part in 28,000 parts water under the conditions 

 of the experiment. 



1 Jahresber, f. Agr. Chern., 1860-1, p. 7. 

 ' 2 Jahresber, f. Agr. Chem., 1860-1, p. n. 



