NITRATE DEPOSITS 143 



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 radio- 

 activity 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 sea- 

 weed 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 condi- 

 tions 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 bro- 

 mine 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 



