'220 CHEMICAL MANUEES. 



TABLE LXIV.— SHOWING COMPOSITION OF CALICHE. 



Yellow salt, pure hard, with small crystals . 

 Yellow salt, pure porous soft, with large crystals 

 Yellow ' aliche, veined with bro^ii 

 White caliche, hard and with small crystals 

 White caliche, porous and large ciystals 

 ^rown caliche, porous and large crystals 



Opinions ditfer as to the method of formation of this deposit, 

 which occupies a surface of about 60,000 hectares (say 150,000 

 acres) and contains about 170,000,000 tons, ililliger's is the most 

 Hkely theory ; he beUeves that the nitrate is formed from the nitrogen 

 of guano deposits, which covered the shores of a great soda water 

 lake by a process analogous to tlrat to be seen in Hungary in our 

 own time. The soda salts of the sea water would simply convert 

 the saltpetre into nitrate of soda. This opinion has in its favour 

 all the facts and circumstances met with in the deposit. Moreover, 

 traces of guano are still found in the crude salts. To extract the 

 crude salt a hole is dug in the ground 50 cm. (20 in.) in diameter; 

 when the saltpetre bed is reached a chamber 90 to 100 cm. (35 to 

 40 in.) in diameter by 30 cm. (say 12 in.) deep, and 150 to 200 kg. 

 (3 to 4 cwt.) of powder inserted. By exploding the powder by 

 means of a fusee, a considerable surface of the deposit is laid bare 

 often on a radius 10 metres (say 40 ft.) from the hole. The 

 crude salt is hand picked, to eliminate stones and fragments of less 

 value ; it is charged into baskets or into trucks, which camels trans- 

 port or draw to the melting workshop. To dissolve the crude 

 caliche three kinds of apparatus are used, viz. : — 



1. Open Cast-iron Pans — Paradas. — These are heated bv naked 

 fires. Two pans 2 metres in diameter (6 ft, 6 in.) 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. Ci/rindrical Vertical Pans — Maquinas. — These are heated by 

 direct injection of steam. They are 8 to 10 metres (26 to 33 ft.), 

 with a diameter of 4 to 5 metres (13 to 16 ft.). Each of these pans 

 yields in twenty-four hours 46 to 148 tons of saltpetre. The 

 clarified solution is poured into wrought-iron crystallizers 4 to 5 

 metres (say 13 to 16 ft.) square and 0-5 metre (say 20 in.) deep; 

 crystallization lasts three to four days. The steam given off con- 

 tains an important amount of iodin-e which can be avoided by an 

 addition of soda. 



