i>*<; /;<; ) /'T/A\ AGRICULTURE, 



crystallisation, but is always somewhat moist as it is slightly 

 deliquescent. The commercial article is usually of a dirty- 

 white colour and is put on the market as 9o% pure. This 

 guarantee is sometim s expressed as 4; less than 5%Befrac- 

 tion," meaning that the impurities chiefly moisture and 

 common salt do not exceed o% of the whole. 



Source. The crude material from which the commercial 

 article is prepared forms great deposits in certain desert 

 districts in Peru, Chili, and Bolivia and goes by the name 

 of u Caliche/' It varies much in composition and may 

 contain anything from 25 to 50 % of nitrate, the rest 

 being earthy and stony matters along with certain salts, 

 chiefly chlorides and sulphates of magnesium, calcium and 

 sodium. 



The deposit is always found comparatively near the 

 surface, lying under a useless covering of gravel, clay, and 

 gypsum, and may vary in thickness from a few inches to 

 ten or twelve feet. Many of the deposits are at high 

 altitudes (3000 to 4000 feet) and at considerable distances 

 inland. Different theories have from time to time been 

 put forward to explain the presence of these deposits. 

 One is that they are residues from the decay of great 

 masses of sea- weed : another, that they are accumulations of 

 salts brought down from higher levels by rivers which 

 have long ceased to exist. 



Preparation. The preparation of nitrate of soda from 

 'Caliche" may be briefly summarised as follows. .The 

 deposit is exposed by blasting with gunpowder. The 

 large masses are broken up and the material is passed into 

 In 1.0*0 ivfinorios wher6 it is extracted with hot water, and 



