22 



BULLETIX 61, U. S. DEPARTMENT OF AGRICULTURE. 



tx) the presence of colloid silica or alumino-silicate, and consists primarily in the direct 

 addition of alkali to these solids, without substitution, insoluble silicates or alumino- 

 silicates being formed.^ 



U^''The loss of an acid radical of a dissolved salt to clay, soil, etc., appears, like the 

 loss of the base, to be due usually to the formation of an ordinary insoluble salt, such 







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Fig. 2.— Diagram showing the factors of loss during the movement of a soluble salt from the weathering 



zone to the sink. 



as the phosphate, carbonate, or silicate of calcium, iron, etc. Such precipitation 

 takes place primarily from alkaline solution, because the acids that have the greatest 

 tendency to form insoluble compounds are weak acids, whose salts are hydrolyzed 

 by water.^ 



* * * "Sodium silicates and alumino-silicates are less stable in contact with 

 water solutions than the corresponding potassium compounds. Evidence of this is 



» Bui. 312, U. 8. Geol. Survey, p. 28. 



« Ibid., p. 30. 



