Nitrogenous Manures 



carried down the nitrate to the lowest level of the 

 plain at the foot of the coast range. The water 

 has evaporated and the beds of salts are left. In 

 this way many superimposed beds of salt have been 

 formed, covered by beds of sand brought down at 

 the same time or deposited by the wind ; and so it is 

 seen that sometimes the salt beds are separated by 

 beds of sand. Generally the beds of salt are about 

 a 3^ard in thickness, but sometimes they are six or 

 seven yards through and even more. To obtain the 

 salt these deposits are blown up by mines. It is 

 called caliche. 



The deposits do not consist entirely of nitrate of 

 soda. The best beds contain from 40 to 50 per cent, 

 of nitrate, those of the third quality, which are the 

 last to be worked, from 17 to 30 per cent. They 

 always contain sea salt, often nitrate of potash, 

 sometimes sulphate of soda, lime, and magnesia, 

 and some impurities. 



Profiting by the indications of differing solubility 

 of the sea salt and the nitrate of soda the workers 

 treat the caliche with boiling water, and the nitrate 

 of soda crystallises in cooling, while the sea salt 

 remains m solution. This water is again treated 

 to extract the iodine, and the day that this was 

 achieved the price of iodine went down by half. 



The nitrate is dried in the sun and put into sacks. 

 This nitrate is coarse and has a dirty appearance, 

 containing a little sea salt, sulphate of soda or 

 magnesia, water, and a few impurities, and about 

 95 per cent, nitrate of soda. It ought to contain about 

 15-5 of nitrogen, should not contain less than 15 per 

 cent, and cannot contain more than 16 per cent. 



34 



