II. J PREPARATION OF NITRATE OF SODA 49 



of the origin of the Chile deposits of nitrate of soda, an 

 examination is required of the salts in the rocks of the 

 Corderillas, the drainage from which would find its way 

 into the plain of Tamarugal. 



The nitrate of soda is found in a deposit named 

 caliche, of which it constitutes from 60 per cent, down to 

 17 per cent, lower grades not being at present worked. 

 In the caliche it is associated with sodium chloride, 

 sulphates of calcium, sodium, and potassium, and a 

 varying proportion of insoluble earthy matter. The 

 caliche is not found on the surface, but is covered by 

 various earthy and gypseous deposits to the depth of 2 

 to 10 feet. After the deposit has been broken up by 

 blasting, the caliche is removed to the works, broken up 

 and lixiviated in large vats heated by steam. The 

 saturated solution is led into tanks in which the nitrate 

 of soda deposits on cooling, further crops being 

 obtained from the mother liquors by continuing the 

 treatment. After draining and drying the nitrate is 

 made up into 2-cwt. bags for export. A further 

 product of the nitrate process is iodine, because the 

 caliche always contains a small quantity of sodium 

 iodate. The nitrate of soda thus obtained is a coarsely 

 crystalline powder, varying in colour from a slight 

 brown or pink shade to a grey-white, containing 95 to 

 96 per cent, of pure sodium nitrate, the remainder being 

 made up of moisture, sodium chloride, and traces of 

 sulphates of sodium, magnesium, and calcium. 



A sample of the crystals after drying in the sun had 

 the following composition : — 



D 



