24 CHEMICAL FERTILIZERS 



and but very little potassium, the chief product is nitrate of 

 soda. The nitrate strata are covered with a few inches of 

 loose-blown dust, under which is a hard rock containing much 

 nitrate, some common salt, magnesia, earth and pebbles. 

 The true caliche is found some 20 or 30 ft. below the sur- 

 face, under which there is a loose layer of gravel, containing 

 no nitrate. Bands of sulphate of lime and clay also occur. 

 Caliche, which varies in thickness and quality, is a mixture 

 of nitrate of soda, a little nitrate of potash, a large amount 

 of common salt, and, very frequently, sulphate of soda and 

 magnesia. A good deposit would consist of a bed, about 

 3 or 4 ft. in thickness, containing from 40 % to 45 % 

 of nitrate. There are, besides, many beds which do not 

 contain more than between 5 % and 20 %, but up to the 

 present these have been little worked. 



The general method of procedure is for a man to clear 

 away the wind-blown dust on the surface, and then cut a 

 round hole, about 9 ins. in diameter, through to the 

 bottom of the caliche. The hole is then enlarged, and a small 

 boy is sent down to clear it out still more, especially at the 

 base. A cup is thus formed underneath, which is filled with 

 gunpowder, and subsequently blown up. After the explosion 

 workmen break up the blocks with crowbars, and fill the 

 material into carts. The composition of the caliche varies 

 considerably, the kinds most commonly worked containing 

 from 20 % to 50 % sodium nitrate, 25 % to 60 % sodium 

 chloride, from 2 % to 20 % insoluble matter, about 5 % 

 sodium and magnesium sulphates, with occasional amounts 

 of iodides, iodates and perchlorates. 



Nitrate of Potash. Nitrate of potash has been one of 

 the important smaller industries of India from very early 

 times ; it depends for its raw material upon earth which is 

 collected from old, as well as from existing, village sites. 

 Indian villages consist of small buildings, chiefly composed 

 of mud, the floors of which are often made by beating down 

 mixtures of mud and cow dung. After many years these 

 mud huts tumble down, and bury considerable quantities 

 of miscellaneous organic refuse. Sometimes the villages 



