46 FERTILISERS CONTAINING NITROGEN [chap. 



share, France and the United States about one-sixth 

 each, and Germany rather more than one-third of the 

 whole. Opinions differ greatly as to the approaching 

 exhaustion of the Chilian deposits ; various estimates 

 set their probable life at from twenty to forty years, 

 but doubtless long before exhaustion sets in the 

 poorer grounds, now being neglected as containing 

 less than the paying amount of nitrate, will be exploited, 

 provided always that the artificial nitrate of lime does 

 not render the whole industry unprofitable. 



As to the origin of the nitrate of soda deposits there 

 are two theories, to understand which some description 

 of the mode of occurrence is necessary. The chief 

 deposit lies in the province of Tarapaca, in Chile, on 

 an elevated plain, about 3000 feet above sea level, known 

 as the Pampa of Tamarugal, which stretches for a breadth 

 of some thirty or forty miles from the Corderillas on 

 the eastward to a low range of foothills separating it 

 from the sea. The climate is intensely dry, rain falling 

 only every two or three years, and then in quantities so 

 small as to evaporate rapidly. The special nitrate-bearing 

 deposit or caliche occurs a few feet below the surface, 

 and in it the nitrate is associated with earthy matters, 

 gypsum, common salt, and sulphates of sodium and 

 potassium. The generally accepted theory regards the 

 plain as an ancient sea-bed elevated by one of the 

 volcanic movements common on that coast, and then 

 desiccated. The nitrate of soda is set down to the 

 oxidation of immense masses of seaweed present in the 

 original sea, the salt of which has provided the necessary 

 sodium base. The chief argument in support of this 

 supposition is the presence of a small amount of sodium 

 iodate in the crude caliche, seaweed being known to 

 contain iodine. But such a theory is as impossible on 

 chemical grounds as it is untenable geologically. It 



