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salty compounds, and as evaporation still continued, the different salts began to deposit on the pampa. in the salitreras and salares, much as they are to-day. Then as a final step sand and rock fragments from neighboring hills covered the beds with their present capping of loose waste.

Other explanations of the origin of the nitrate have been advanced. One ascribes it to natural chemical processes accompanying decomposition of different minerals. Another suggests that the wonderful electrical discharges in the Andes are responsible, for the odor of nitric acid in the air is not uncommon after severe electrical storms, and electricity even now is being used to extract nitrogen from the air. But the enormous amounts of nitrate in Chile and the geological conditions of its occurrence fit in best with the idea of origin from guano, as stated above.

The fertilizing value of these nitrates is supposed to have been known to the Peruvian Incas, but not generally to have been taken advantage of by them. Tradition also says that Bolivian Indians at an early date came down from the plateau after nitrate to use on their crops, and it credits them, rather doubtfully, with having developed a primitive form of refining. Rich pieces of caliche, so the story runs, were boiled with water in great earthen pots, called cachuchos, after which the solution was allowed to cool and evaporate until crystallization of nitrate resulted. Fairly pure nitrate can be secured in this way. Some of the earliest manufacturers for commercial purposes are said to have followed almost the same method, and the principle is exactly like that of the modern process. Even the name "cachuchos" still persists, though the great steel or iron boiling tanks of to-day scarcely suggest "earthen pots."

Prior to the nineteenth century the outside world knew little or nothing