May, '14] 



GRANITIC SOIL POTASSIUM. 



19 



Table XI 



No new salts appear in solution and the water extract gives no 

 evidence of the nature of the reaction. By analogy, however, 

 the reaction must be chemical. When potassium exchanges 

 places with calcium and magnesium, these in turn form phos- 

 phates which have a very low solubility and do not appear in the 

 solution. This is further substantiated by the fact that, where 

 large amounts of calcium sulphate are formed, not all of the acid 

 radical appears in solution. 



The data in Tables X and XI were obtained as in Table IX 

 by adding to the soils di-potassium phosphate in solution and 

 bringing the moisture content up to 20% by the addition of 

 water. The samples were thoroughly mixed, placed in sealed 

 jars, and allowed to stand for several weeks. They were then 

 shaken with water and the amount of soluble potassium deter- 

 mined. 



It has been shown in Table VIII that when potassium chloride 

 is percolated through columns of soil, potassium is removed 

 from solution and retained in the soil. The solubility of the soil 

 potassium is therefore not increased by such a solution. A num- 

 ber of solutions of different salts were percolated through the 

 soils to determine what effect they might have on the solubility 

 of the soil potassium. For these experiments, solutions were 

 made of sodium nitrate, sodium chloride, sodium carbonate, and 

 commercial acid phosphate. The strength of these solutions was 

 the same as that of the potassium chloride used in Table VII 

 on the basis of the potassium equivalent. The amount of soil 

 was also 500 grams. The data obtained from these experiments 

 follow: 



