NITROGEN 



129 



they were formed comparatively recently and are due 

 to the nitrification of marine vegetation; that continued 

 leachmgs from soils accumulated in great lakes in which 

 much vegetable material grew and accumulated; and that 

 finally these lakes became isolated, and evaporation and 

 rapid nitrification took place. The presence of iodine in 



FIG. 49. Deposit of nitrate crystals in the pans of Fig. 48 after the 

 liquor is run off. 



the caliche would seem to support the theory of marine 

 formation. There are a number of impurities in the natural 

 sodium nitrate, among which are organic matter, common 

 salt, calcium sulphate, and insoluble silica. 



Some niter deposits have been found in California, 

 though these are not of so high grade as those of Chili. 

 An average of more than a hundred analyses of these Cali- 



