128 CHEMISTRY OF FARM PRACTICE 



generally in the soils of arid or semi-arid regions, but only 

 in a few regions is there a percentage high enough to war- 

 rant their leaching and purification. Very extensive de- 

 posits are located on the western coast of South America, 

 principally in Chili, whose government derives a large 

 income from this source. The deposit is called caliche, 



FIG. 48. General view of crystallizing pans for obtaining nitrate of 

 soda. Each pan has about 500 cu. ft. capacity and 225 sq. ft. 

 cooling surface. 



and occurs at depths ranging from 10 inches to 16 feet from 

 the surface of the soil. The layers containing the sodium 

 nitrate vary in thickness from 6 inches to 3 feet. This 

 material is generally covered with a kind of conglomerate 

 rock called costra. These beds are from 15 to 90 miles 

 distant from the sea-coast and extend 220 miles in length 

 and in some places 2 miles in breadth. It is believed that 



