There are many of these mills throughout the nitrate fields, and they are busy places. The lumps are first crushed, and are then lifted by elevators and placed in huge tanks filled with sea water. These tanks are encircled by coils of steam pipes, which heat the water that is poured in with the rock to any desired temperature. Nitrate is soluble in water, and this purifying process rests upon the fact of its greater solubility in water heated to the boiling point, than the other salts with which it is associated. When the water has become supersaturated in the boiling tanks, the nitrate of soda in solution is drawn into shallow vats which are exposed to the air. At this state it looks like pale maple molasses. As it cools, the nitrate of soda crystallizes in the vats, together with a little common salt and a small amount of other impurities, and the sides become covered with white sparkling crystals like alabaster. These crystals are then shovelled upon drying boards and exposed to the sun for a time, after which they are graded and put into bags weighing a little over a hundred pounds each. This product, which is ninety-six per cent. chemically pure nitrate of soda, is then transported to the seacoast, from whence it is shipped to Europe or the United States, the latter country receiving about one-fifth of the whole. Another product of these nitrate beds is iodine, which remains in the liquid after the removal of the nitrate. This liquid is poured into smaller pans, and is chemically treated until the iodine is precipitated in the form of a black powder. This is then heated in a retort which changes it to a vapour, and it is again condensed into beautiful violet crystals. The iodine is packed in small casks which are shipped with bullion and other valuables, for each cask is worth several hundred dollars. As the consumption of iodine is not very large the _oficinas_ refine only a part of the iodine in order to keep up the price. More than two million tons of nitrate of soda were shipped from Chile last year, which is the greatest amount that has ever been produced. It has been found especially valuable for increasing the growth of the sugar beets in Europe, as it seems to provide the soil with the essential elements for their growth. The consumption in the United States is increasing rapidly, and it is looked upon as the best fertilizer provided by nature. According to horticultural authorities it has been found especially efficacious in stimulating the growth of vegetables, such as cabbages, onions, carrots, beets, etc., and for field crops of many kinds. It is said that even the Incas of Peru were acquainted with its value as a fertilizer. It is also extensively used in the manufacture of gunpowders and other high explosives, which in itself makes a considerable demand.