24 R. A. F. PENROSE, JR. 



often goes over the property again more carefully in search of what is 

 left. In this way many properties have been worked over several 

 times, and lower-grade material has been taken each time. In a 

 few cases, even the costra, when it contains an unusual amount of 

 nitrate, has been used after the purer parts of the deposits have been 

 exhausted. 



In the early days, only the richest of the deposits were worked, 

 and only crude nitrate running as high as 40 or 50 per cent, in sodium 

 nitrate was mined, but now much lower grades are worked, and the 

 average of the crude material used in the Tarapaca region today 

 would run, perhaps, below 25 per cent, in nitrate. Of course both 

 richer and poorer material is also worked, and in certain places crude 

 nitrate running even as low as 10 per cent, is utilized in admixture 

 with higher-grade material. 



The crude nitrate is hauled in carts or on tramways from the 

 mines to the refineries, where it is coarsely crushed and the nitrate 

 separated from the impurities by a process of leaching with hot water. 

 The refined product usually contains about 95 per cent, of sodium 

 nitrate, which is the standard of purity for the nitrate shipped from 

 the district. Sometimes a still higher-grade product is made for 

 special purposes. The nitrate is put in large sacks, and sent to the 

 coast for shipment to various parts of the world. Sodium nitrate 

 is deliquescent, so that when exposed to the moist air on board ships 

 it cakes and the sacks stick together, often forming a solid mass which 

 has to be taken out of the ships with picks. 



The method used in extracting the nitrate is very crude, only 

 from 60 to 70 per cent, of it being saved, and the average loss of 

 nitrate in the Tarapaca region in refining is said to be about 35 per 

 cent. Those in authority claim that under present conditions, the 

 nitrate that is lost could not profitably be saved, but the time may 

 come when the crude nitrate will show signs of exhaustion, and then 

 probably less wasteful methods will be devised, and the loss will be 

 cut down. At present, the supply of crude material is so vast that 

 such economy has not been forced on the producers. 



The iodine is obtained from the solution (mother liquor), after 

 the nitrate has been taken out, by concentrating it and treating it 

 with sodium sulphites, which precipitate a black powder consisting 



