MANUTAOTTTEB OP NITRATE OF SODA. 279 



The boiler, flues, and setting, are constructed on Livet's 

 system, and give excellent results. They are built in pairs as 

 regards flues, with a chimney 42 feet high by 5 feet in diameter, 

 of iron, having a base of 9 feet for each pair of boilers. 



The feed-water tank, fresh-water tank, top mother-liquor 

 tank, and weR- water tank, are all erected on substantial masonry 

 built on deep concrete foundations, and rest directly on a bed 

 of cement. 



The ninety crystallizing tanks, or precipitating tanks, 16 

 feet by 16 feet, by 3 feet deep on one side, sloping to 2 feet 

 9 inches on the other, in order to thoroughly drain the precipi- 

 tated nitrate, are erected on a strong framework of Oregon pine 

 6 inches square in section, with longitudinal, transverse, and 

 diagonal stays, 4 inches square in cross-section. Under each 

 crystallizing tank there are six runners of timber, 4 inches 

 square, on which it rests, on the projecting ends of which is a 

 plank roadway for the men in charge of the hot nitrate in 

 solution, known as "caldo," literally boiling juice. This consists 

 of "caliche" dissolved in boiling mother-liquor. All the crystal- 

 lizing tanks with framework rest on low stone walls built on a 

 dry rubble foundation, cement being in this case unnecessary, as 

 leakage from mother-liquor or nitrate in solution does not dis- 

 solve the ground on which it falls. 



The whole of the known nitrate deposits in the world are 

 situated on the west coast of South America, between south 

 latitude 19° and 27°, although there are indications of nitrate in 

 Nevada and California. 



The "caliche," or raw nitrate of soda, is a mineral deposit 

 formed, it is alleged, by the contact of decomposing animal and 

 vegetable matter with the salts left on the retreat of the sea. 

 This theory of its formation is supported by the frequent dis- 

 covery of guano, sea-birds' eggs, fishes, feathers, birds' skeletons, 

 shells, fossils, &c., in proximity to the caliche, and at a depth 

 of 12 to 15 feet below the surface of the ground, and also by the 

 presence of iodine as iodate of soda, which is peculiar to 

 the sea. 



The best deposits are found on the skirts of the Tamarugal 

 Pampa. The caliche lies in beds of a thickness varying from 



