NITROGENOUS MANURES 



261 



of gravel and clay. The whole is blasted out by charges 

 of dynamite placed underneath the caliche, which is after- 

 wards separated mechanically from the fragments of 

 the covering layers. It is then lixiviated with water 

 to separate the earthy and insoluble matters, and the 

 nitrate of soda is crystallised out from saturated solutions 

 and dried in the sun. Iodine and other salts are recovered 



from the mother liquors in considerable quantities. A 

 general view of the nitrate and iodine plant is shown in 

 the illustration 1 (Fig. 32). The occurrence of iodine along 

 with the nitrate of soda is regarded as confirming the view 

 that the organic matter from which the latter originated 

 consisted of seaweed. 



The nitrate fields are very extensive. Upwards of 



1 From "The World's Work," March, 1909. 



