MINERALS USED AS FERTILIZERS. 67 



the pans ; the nitrate is afterward farther purified by crystallization. 

 As brought into commerce for agricultural purposes it constitutes a 

 moist gray saline mass, somewhat resembling common salt, of which 

 substance it usually contains a few per cent ; occasionally also a small 

 amount of sodic perchlorate (which acts injuriously on vegetation). 

 Aside from its use as a fertilizer, Chile saltpeter serves for the man- 

 ufacture of nitric acid ; and either directly, or after previous transform- 

 ation into potassic nitrate, for that of gunpowder. 



The Chilean locality is the only one from which the commercial 

 article is derived ; the deposits elsewhere are too limited in extent to 

 compete commercially with the South American product. Caliche 

 ranging as high as 8o r / of nitrate of soda has been sent to the writer 

 from the Colorado Desert in Southern California, but the exact locality 

 of occurrence has not been divulged. Extended areas of clay hills 

 impregnated with nitrates exist in the Death Valley region of California, 

 but in the absence or extreme scarcity of water in that region, it is 

 doubtful whether these impregnations can be made practically available. 

 Another locality is that near White Plains, Nevada, where Caliche 

 averaging about S% purity is found in cavities and crevices of a reddish 

 volcanic rock. The rainfall in this region is so slight that the greater 

 part of the dust or sand blown about by the wind consists of Glauber's 

 salt. Here also, as in Chile, the niter deposits appear to be restricted to 

 within a short distance from the surface, and the total amount thus 

 far observed appears to be insufficient to encourage large-scale ex- 

 ploitation. 



Origin of Nitrate. Deposits.- The probable origin of these niter 

 deposits has given rise to a great deal of discussion, and a wide differ- 

 ence of opinion exists as to the source from which the nitrogen may 

 reasonably be supposed to have been derived. According to the 

 present state of our knowledge, it must be presumed that its sources 

 have been organic, and that the niter has been produced by the activity 

 of the same bacteria which now produce nitrates in our soils, rendering 

 the nitrogen of humus available to plants. But it is by no means clear 

 what that organic material could have been ; for at the present time 

 the plateau of Tarapaca is almost wholly destitute of vegetation, if not 

 of animal life. The latest and apparently most reasonable suggestion 

 is that of Kunfze, who calls attention to the fact that the vicunas and 

 llamas which are at home in this portion of the Andes, and are known 

 to have roamed over that region in countless herds, have the curious 

 habit of always depositing their manure in one and the same place 



