BORATE DISTRICTS OF PERU. 



117 



(magnesian alum), mixed with earthy matters, as silica, alumina, carbonate 

 and sulphate of lime ; also iodine, bromine, chrome, and boracic acid mineral. 



HI. Coba is the general loose earthy covering to the silico-calcareous and 

 porphyritic rocks, and here at the Noria the borate is found in nodules, 

 front the size of a pea to two feet in diameter. In some parts of the Coba 

 the borate is seen in thin stria? with sulphate of lime. 



In this region it appears to me, that salt and other saline matters, includ- 

 ing boracic salts, have been formed in the Andes, and brought down by 

 streams and percolation. (The almost pure chloride of sodium on the 

 mountains of the coast I have supposed to be mainly indebted to the salt 

 vapours of the ocean). There is scarcely a trace of organic matter in the 

 soil, to afford nitrogen to change the salt into nitrate. Ought we not rather 

 look to the atmosphere for nitrogen, and the various chemical changes 

 resulting from solar heat, dews, and occasional slight rains. 



The salt of the Salares is a mixture of various saline substances ; and, as 

 there is abundance of calcareous minerals, the nitrogen of the air may give 

 rise to nitrate of lime, then the change will be as follows : — 



Nitrate of Soda. 



Nitrate of Lime. 



Nit. Acid. 



Sodium 



Oxygen. 



Lime. 



Chlorine. 

 Hydrogen. 



Chloride of 

 Sodium. 



Water. 



Chloride of Calcium, or Muriate of Lime. 



The saliteros say that one may almost see the salt of the Salares 

 transformed into nitrate. A salitero observed to me that he could not tel 

 where the salt came from, but he believed the nitrate was formed by light 

 rains trickling through saline and earthy matters, turning the salt into 

 nitrate. Some caliches when quarried are called green, and on exposure to 

 the air ripen, yielding the nitrate more easily. Sometimes the salt and 

 caliche has a yellow, pink, or green colour, caused, I think, from chrome. 



[Manufacture of Nitrate from Caliche. — The nitrate grounds are 

 known to be on the edges of the salares and rising ground : at the Noria 

 water is within a foot of the salar. There are some nitrate grounds without 

 any apparent salar, and where water is now thirty to forty yards deep, and 

 even deeper ; but salt has been there to form the nitrate. 



Having Cateado, hunted for, and found the nitrate ground, habitations are 

 built of salt from the salar, wells are dug, the water being extracted by 

 Norias ; paradas or iron boilers in pairs are fixed ; depositos or settling 



