396 KEPORT OF NATIONAL MUSEUM, 1899. 



within which the deposits lie, is covered by an alluvial soil rich in 

 organic matter. This organic matter under the now well-known action 

 of bacteria, aided by the prevailing high temperatures of the region, 

 gives rise to nitrates, which owing to the absence of rains for long 

 periods, accumulates to an extent impossible under less favorable 

 circumstances. Mountain floods which occur at periods of seven or 

 eight years, swamp the plain, bringing in solution the nitrate drained 

 from the soils of the surrounding slope, and to accumulate in the 

 lower levels. On the evaporation of the water this is again depos- 

 ited. The occurrence of the nitrate so far up the slope of the hills is 

 regarded by Newton as due to the tendency of the nitrate salt, in 

 saturated solutions, to creep up, as in experiment it may be seen to 

 creep up and over the sides of a saucer or other shallow dish in which 

 the evaporation is progressing. 



BIBLIOGRAPHY. 



M. A. MTJNTZ. Recherches sur la formation des gisements de nitrate de soude. 



Comptes Rendus de 1'Academie des Sciences, CI, 1885, p. 1265. 

 ROBERT HARVEY. Machinery for the Manufacture of Nitrate of Soda. 



Journal of the Society of Chemical Industry, IV, 1885, p. 744. 

 RALPH ABERCROMBY. Nitrate of Soda, and the Nitrate Country. 



Nature, XL, 1889, p. 186. 

 . The Nitrate Deposits and Trade of Chile. 



Engineering and Mining Journal, L, August 9, 1890, p. 164. 

 NICOLAS RUSCHE. Die Saltpetrewiiste in Chile. 



Vom Pels zum Meer, pt. 4, 1891-2. 

 G. M. HUNTER. The Santa Isabel Nitrate Works, Toco, Chile. 



Transactions of the Institute of Engineers and Shipbuilders of Scotland, 

 XXXVI, p. 57. 

 WILLIAM NEWTON. The Origin of Nitrate in Chile. 



The Geological Magazine, I [I, 1896, p. 339. 

 W. H. HESS. The Origin of Nitrates in Caves. 



Journal of Geology, VIII, No. 2, 1900, p. 129. 



X. BORATES. 



Of the ten or more species of natural borates but three, or possibly 

 four, are commercial sources of borax, and need consideration here. 

 These are, (1) borax or tincal; (2) ulexite, or boronatrocalcite; (3) 

 priceite, colemanite, or pandermite, and (4) boracite, or stassfurtite. 

 Sassolite, or native boric acid, occurs chiefly in solution. The inti- 

 mate association of these minerals renders it advisable to treat of their 

 origin and mode of extraction in common, after giving the composition 

 and general physical characters of each by itself. 



1. BORAX OR TINCAL; BORATE OF SODA. 



Composition Na 2 B,O 7 .10H 2 O,= boron trioxide, 36.6 per cent; soda, 

 16.2 per cent; water, 47. 2 per cent. Color, white to grayish, and 

 sometimes greenish; translucent to opaque. It crystallizes in short, 



