. Popular science monthly. ize on the surface, so a stirring boy, or rayandero, isemployed to break up the film and make it settle. Five or six days arenecessary to complete the crystallizing process. A large plant mayhave 300 or more bateas, capable of holding more than 1,000,000 gallonsof caldo, and yielding at each full charge as much as 2,500 tons ofnitrate. When crystallization has gone as far as it will, a valve in the bottomof the batea is opened and the liquid is drawn off, leaving behind a thicklayer of glistening white crystals. This is the nitrate or salitre ofcommerce, being 95 per
. Popular science monthly. ize on the surface, so a stirring boy, or rayandero, isemployed to break up the film and make it settle. Five or six days arenecessary to complete the crystallizing process. A large plant mayhave 300 or more bateas, capable of holding more than 1,000,000 gallonsof caldo, and yielding at each full charge as much as 2,500 tons ofnitrate. When crystallization has gone as far as it will, a valve in the bottomof the batea is opened and the liquid is drawn off, leaving behind a thicklayer of glistening white crystals. This is the nitrate or salitre ofcommerce, being 95 per cent, or more of pure nitrate of soda; theremainder is largely water and salt. The liquid which is drawn off,known as agua vieja, or mother liquor, still contains a large amount ofnitrate in solution, and is used over and over again in the boiling fact, no water is ever thrown away, the only loss being that whichpasses into steam from the boiling tanks and evaporates from the crys- 222 THE POPULAR SCIENCE MONTHLY. Photograph loaned by Mr. C. E. Atwood, Antofagasta, Chile. Nitrate in the cancha, being bagged and put on cars for the left background, a big accumulation of ripio. tallizing pans. The finished nitrate is shoveled from the bateas intocars, drawn to the deposit, or canclia, and there after drying for severaldays is bagged ready for shipment. Shipment in bulk is impracticablebecause the nitrate so readily absorbs water. Even when shipped insacks it sometimes becomes caked in the holds of ships and has to betaken out with picks. From the agua vieja, iodine is extracted by a simple process of pre-cipitation with chemicals (mainly sodium sulphites). It figures onlyas an important by-product of the industry, for the iodine trustmakes an annual allotment to each establishment, commonly less thanwhat could be made in a month, if there were no restrictions onproduction. The .only other important step in the refining of nitrate is the clear-ing and recharg
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