262 



SOILS AND MANUBES 



twenty million tons have already been excavated, and 

 according to a report made to the Chilian government 

 last year, it is estimated that there are some 220 million 

 tons still left. At the present rate of production, or even 

 allowing for the probable increase, it will take more than 

 100 years to exhaust the supply. 



The first shipment of nitrate of soda, which took place 

 from the port of Iquique in 1830, amounted to only 

 800 tons. The discovery of the nitrate fields appears to 

 have been made some years before that date. Ten years 

 later, in 1840, the annual rate of export had risen to 

 over 10,000 tons, in 1890 it had increased to over a 

 million tons, and in 1907 the total quantity exported 

 amounted to 1,660,000 tons. 



The following table shows the quantities of nitrate of 

 soda imported into the United Kingdom during the last 

 ten years : 



Composition and General Properties. Pure nitrate of 

 soda contains 16*47 per cent, of nitrogen, equal to 20*0 

 per cent, of ammonia, and is a colourless crystalline 

 salt. The commercial product usually contains about 

 95 per cent, pure nitrate of soda, which is equal to 

 15*65 per cent, of nitrogen. The bnlance consists mainly 

 of water, which usually forms 2 or 3 per cent., and 

 chlorine, equal to from ^ to 1 per cent, of sodium 

 chloride. Small quantities of sulphates, magnesia, lime, 



