THE WASTE AND CONSERVATION OF PLANT FOOD. 227 



At the present time the collection and export of saltpeter from Chile 

 IS a business of great importance. The largest export which has ever 

 taken place in one year was in 1890, when the amount exported was 

 927,290,430 kilograms; of this quantity 642,506,985 kilograms were sent 

 to England and 86,124,870 kilograms to the United States. Since 

 that time the imports of this salt into the United States have largely 

 increased. 



According to Pissis ■ these deposits are of very ancient origin. This 

 geologist is of the opinion that the nitrate deposits are the result of the 

 decomposition of feklspathic rocks; the bases thus produced gradually 

 becoming united with the nitric acid provided from the aii\ 



According to the theory of Nollner^' the deposits are of more modern 

 origin and due to the decomposition of marine vegetation. Continuous 

 solution of soils beneath the sea gives rise to the formation of great 

 lakes of saturated water, in which occurs the development of much 

 marine vegetation. On the evaporation of this water, due to geologic 

 isolation, the decomposition of nitrogenous organic matter causes gen- 

 eration of nitric acid, which, coming in contact with the calcareous 

 rocks, attacks them, forming nitrate of calcium, which, in presence of 

 sulphate of sodium, gives rise to a double decomposition into nitrate of 

 soda and sulphate of calcium. 



The fact that iodine is found in greater or less quantity in Chile salt- 

 peter is one of the chief supports of this hypothesis of marine origin 

 inasmuch as iodine is always found in sea plants and not in terrestrial 

 plants. Further than this, it must be taken into consideration that 

 these deposits of nitrate of soda contain neither shells nor fossils nor 

 do they contain any phosphate of lime. The theory, therefore, 'that 

 they were due to animal origin is scarcely tenable. 



Lately extensive nitrate deposits have been discovered in the United 

 States of Colombia.^ These deposits have been found extending over 

 30 square miles, and vary in thickness from 1 to 10 feet. The visible 

 supply is estimated at 7,372,800,000 tons, containing from 1 to 13 5 

 per cent of nitrate. The deposits consist of a mixture of nitrate of 

 soda, chloride of soda, sulphate of calcinm, sulphate of alumina and 

 insoluble silica. It is thought that the amount of these deposits will 

 almost equal those in Chile and Peru. 



PHOSPHATIC DEPOSITS. 



Gautier^ calls attention to the fact that the oldest phosphates are 

 met with m the igneous rocks, such as basalt, trachyte, etc., and even 

 m granite and gneiss. It is from these inorganic sources, therefore, 

 that all phosphatic plant food must have been drawn. In the second 



' Fucus and De Launy. Traitd des Gltes Mineraux, 1893, Vol. 1 pa-e 4'>5 



2 El 8alitre de Chile, Rene F. Le Feuvre y Artnro Daoino, 1893 pa-e I'' 



3 Bureau of American RepnMics, Monthly Bulletin, December. 1893rpage 18 et seq. 



■•Compt. Rend., 116, pages 1:371, 6. 



