NITROGENOUS MANURES 89 



fact that its acid is combined with another al- 

 kali. In Indian saltpetre it is combined with 

 potash, while in Chili saltpetre it is combined 

 with soda. It is met with in the Pampas of Peru, 

 of Chili and Bolivia, between 19 and 27 degrees 

 of south latitude; it abounds especially in the 

 province of Tarapaca (formerly Peruvian, now 

 Chilian), and in the desert of Atacama. The 

 nitrous mineral caliche or terra saltrosa, occurs 

 as a layer 1 to 6 in. thick under a bed of con- 

 glomerate, consisting of sand, feldspar and peb- 

 bles, amalgamated by a cement consisting of 

 clay and different salts forming a bed 20 to 30 

 in. thick. Its color varies from gray to brown. 

 The conglomerate bed is sometimes wanting, 

 so that the mineral crops out at the surface. 



The caliche is never pure nitrate of soda. 

 It contains mixtures of nitrate of potash, com- 

 mon salt, iodide and bromide of sodium, alkaline 

 sulphates and sulphate of lime mixed with sand. 

 It only contains on an average 25 per cent of 

 nitrate. Picked pieces contain more. 



Opinions differ as to the method of formation 

 of this deposit which occupies a surface of about 

 150,000 acres and contains about 170,000,000 

 tons. It is believed that the nitrate is formed 

 from the nitrogen of guano deposits, which 

 covered the shores of a great soda water lake 

 by a process analogous to that to be seen in 

 Hungary in our own time. The soda salts of the 

 sea water would simply convert the saltpetre 



