NITROGENOUS MANURES 91 



crude salt a hole is dug in the ground 20 in. in 

 diameter; when the saltpetre bed is reached a 

 chamber 35 to 40 in. in diameter by 12 in. deep is 

 excavated and 3 to 4 cwt. of powder inserted. By 

 exploding the powder by means of a fuse, a con- 

 siderable surface of the deposit is laid bare often on 

 a radius of 40 ft. from the hole. The crude salt 

 is hand picked, to eliminate stones and frag- 

 ments of less value; it is charged into baskets 

 or into trucks, which camels transport or draw 

 to the melting workshop. TO dissolve the crude 

 caliche three kinds of apparatus are used: 



1 Open Cast-iron Pans Paradas. These are 

 heated by naked fires. Two pans 6 ft. 6 in. 

 in diameter are used for one furnace. Well 

 water or water from a previous operation is 

 run in, then it is charged with caliche or crude 

 saltpetre reduced to pieces the size of the fist. 

 When the solution is concentrated enough, it 

 is run into cases or boxes, where it clarifies; it 

 is/ then decanted on the top of the depot and 

 run into iron or wooden crystallizers; 40 per 

 cent of crystals is thus obtained and 60 per cent 

 of mother liquor. 



2 Cylindrical Vertical Pans Marquinas. 

 These are heated by direct injection of steam. 

 They are 26 to 33 ft. with a diameter 13 to 16 

 ft. Each of these pans yields in 24 hours, 45 to 

 148 tons of saltpetre. The clarified solution is 

 poured into wrought iron crystallizers 13 to 16 

 ft. square and 20 in. deep; crystallization requires 



