23 
BULLETIN 61, U. S. DEPARTMENT OF AGRICULTURE. 
to 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. 1 
12/' The loss of an acid radical of a dissolved salt to clay, soil, etc., appears, like the 
loss f 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. 2 
* "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. S. Geol. Survey, p. 28. 
* Ibid., p. 30. 
