Page:Popular Science Monthly Volume 83.djvu/214

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 Sketch map of northern Chile, showing approximate location of nitrate lands (black areas). Cross-lined area on small map of South America shows location of nitrates province.

white compound, salty and bitter to the taste, like some sea plants, and capable of absorbing a great amount of moisture. Chemically the substance is sodium nitrate. Pure nitrate is found only in small quantities or "pockets." Commonly it is mixed with earthy materials and various saline compounds, as common salt, Glauber's salt and borax. A small amount of iodine compounds also are present in most cases. This impure raw material is known as caliche to the nitrate miner.

Caliche, unlike many raw forms of minerals, is easy to get at, for it lies on or near the surface. In some places, the caliche is covered with 25 or 30 feet of fine dust (chuca) and coarser rock waste (costra) which must be thrown aside by the minor. In such places, an area which