208 



ANNUAL, REPORT SMITHSONIAN INSTITUTION, 1923 



nitrate will be dissolved while the other salts, if already in solution, 

 will be precipitated. The solution is then allowed to cool and, due 

 to the solubility characteristics mentioned above, the nitrate crytal- 

 lizes out first while the other salts remain in the solution, which is 

 drained off. The nitrate, now in solid form, is placed in drying pans 

 to allow the remaining water to evaporate, and when entirely dry it 

 is packed in bags of about 200 pounds each and shipped by rail down 

 to the different harbors for export. 



Most of the Chile saltpeter is used for fertilizer purposes, the nitro- 

 gen contained therein being extremely soluble and readily available 

 as food for plants. The nitrogen in this form is thus directly and 

 immediately available and no further changes are necessary. 



Considerable amounts of Chile saltpeter are also used for industrial 

 purposes, in which case it must be converted in some other form, the 

 starting point as a rule being nitric acid. This conversion is ac- 

 complished by treating the sodium nitrate with sulphuric acid, when 

 a violent reaction takes place, with the result of the formation of 

 nitric acid which is given off as a gas. This passes into condensers 

 where it is condensed to liquid acid. The reaction takes place accord- 

 ing to the formula : 



NaN0 3 +H 2 S0 4 =HN0 8 +NaHS0 4 



STATISTICS 



Chile saltpeter was first exported from Chile in 1830, but the 

 amount was small, only a few thousand tons per year. Since then it 



has, however, constantly increased as seen from the foregoing tabula- 

 tion, which also gives the export to the United States and its equiva- 

 lent nitrogen content in net tons. 



It is interesting to note how the export dropped in 1915, when the 

 supply of the Central powers in Europe was cut off, and how it 

 since steadily increased until the end of the war, when it again took 

 a big drop. 



