Page:Popular Science Monthly Volume 85.djvu/147

Rh a few years ago. It was observed that pieces of glass left on the ground in the vicinity of the saltpeter mines in the Province of Aconcagua, Chile, became colored blue in a short time, while samples of the same glass exposed on the roofs of buildings to the direct rays of the sun remained colorless. This suggested the possibility of the soil in the vicinity being strongly radioactive, which was thought to be confirmed by the action on photographic plates properly protected and subjected to an exposure in the ground for a month. It was suggested that the radioactivity of the soil as indicated by these experiments might have had something to do with the formation of nitrates in this part of Chile. It is now known that all soils are slightly radioactive and to approximately the same extent.

None of these views which have suggested an inorganic mode of formation for the Chilean nitrates have received very general acceptance. Much more credence is given to the theories that the nitrates found in the deserts of northern Chile have resulted from the decomposition of organic matter brought into the basins in which they are found from outside sources.

One of the most popular of these theories suggests sea-weeds as the source of the nitrates. The explanation is given that in past ages the pampa regions were sea beaches, and that an enormous amount of seaweed was piled up on them. In course of time the beaches were elevated above sea-level, and the collected sea-weeds in decaying under arid conditions decomposed in such a way that the nitrogen present was converted into nitrates, and the iodine into iodates. It may be pointed out in this connection that immense groves of giant kelps are now to be found along the Pacific Coast of North America, and that the proportion of iodine to potash in the dry plants is about the same as is to be found in the crude niter of Chile. The ratio of nitrogen to potash in the former, however, is very much less than in the latter.

There are many objections which may be offered to this theory. Thus, if the niter came from sea-weed it must necessarily contain bromine as well as iodine, since both are present in this source, and there is no known natural process which can bring about the separation of bromides and iodides. So far as known, however, bromine has not been found in any of the nitrate deposits of Chile; whereas, from analyses made by the writer, the bromine in the giant kelps of the Pacific, for example, is of the same order as the iodine.

Again, sea shells are never found in the nitrate beds, and the stones in the neighborhood are sharp and jagged and show no signs of being worn by water as they must necessarily have been if they had at one time existed on a sea beach.

Perhaps the best known theory which has been advanced to explain the origin of these nitrates is that they have been derived from the