Page:Popular Science Monthly Volume 85.djvu/146

142 The source of these deposits is a subject which has given rise to a great deal of discussion. Many theories have been advanced to account for the origin of the nitrates, but all appear to fall short of adequately accounting for all the conditions under which the nitrates are found in Chile. It is generally considered that an organic source is the most probable, but there have not been lacking explanations for the formation of these nitrates which have been based on inorganic agencies.

Thus one of the theories advanced is that the nitrates may have resulted from electric storms occuring in the Andes. It has been suggested that the nitric acid which is formed in this way by the oxidation of the nitrogen of the air becomes changed into calcium nitrate on coming in contact with the limestone of the mountains, and that this in turn on being washed down into the pampa region has been converted into sodium nitrate in coming in contact with the sodium salts already existing there. It has also been stated that at certain seasons of the year there is a great deal of static electricity in the air over the desert region, owing to the strong winds and the extremely dry climate, and that the nitric acid which is formed as a result of this condition is carried to the ground by the moisture in fogs which drift in from the sea.

The view has also been advanced that the nitrogen in the Chilean nitrate may have come from nitrogenous fumes given off by volcanoes in the Andes. It has already been pointed out that nitrides and ammonium salts are sometimes found in the vicinity of volcanoes after an eruption, but whether these compounds result from the direct fixation of atmospheric nitrogen near the mouth of the volcano, or from some combined form of nitrogen already present in the earth is not known, but the former view is the more probable. It has been shown, however, that the source of the nitrogen is not organic.

It has been claimed by some that alkali carbonates are able to bring about the fixation of atmospheric nitrogen into nitric acid in the presence of oxidizable matter, and Pissis expressed the opinion that the niter beds in Chile were formed in this way. It was pointed out that the decomposition of feldspar rock in the region of the Andes supplied alkali carbonates, while the protoxide compounds of iron which are common in the rocks of the pampa are easily oxidized under ordinary conditions to form peroxide compounds of iron. The view was accordingly put forward that the alkali carbonates in contact with rocks of this kind brought about the oxidation of the nitrogen of the air with the ultimate formation of nitrates.

Perhaps the most far-fetched attempt at an explanation of the origin of these deposits was that presented by a writer in the Comptes Rendus