Nitrate of This now constitutes one of the principal sources of inorganic nitrogen in artificial manures, having largely taken the place of Peruvian guano, which was used for many years, and the profitable use of which did much to promote the extensive use of COM mercial fertilizers. The salt occurs in the crude condition called caliche, in enormous deposits, principally in the province of Tarapaca in northern Chile. The earlier records of these deposits extend back to 1820, but it was not until several years later that they were ex ploited. The portion of the country in which the deposits lie is a sandy desert where rain never falls. The altitude is 3,000 to •4,000 feet above the sea-level. The deposits have been attributed to the action of minute organisms fixing in the soil, through countless ages, the nitrogen of the atmosphere, and leaving the product finally in the form of sodium nitrate that has crystallized out of solution in which it has at some time been held. Several other theories have been advanced but no wholly ade quate explanation has yet been offered.
The raw product is found beneath a covering consisting of two layers, the upper one of sand and gypsum and the lower of baked clay and gravel. The thickness of the caliche varies from a few inches to 12 feet. It is extracted by boring through the upper layers and intro ducing a charge of blasting-powder, which, when fired, exposes a considerable quantity of the material. The nitrate is somewhat purified by crystallization before shipping. Iodine is a by-product in the purification process. The nitrate, when ready for shipment, contains about 96 per cent sodium nitrate, or about 16 per cent of nitrogen, 2 per cent of water, and small amounts of sodium chloride, sulphates, and insoluble matter.
The development of the nitrate industry may be appreciated from the fact that the product, which amounted in 1884 to 550,000 tons, increased to 1,000,000 tons in 1890, and to 1,660,000 tons in 1907. The output is ex ported almost entirely to Europe arid the United States. It is held by persons who have examined these deposits that at the present rate of mining they will be exhausted by the year 1930, in which case a serious deficiency in fer tilizer nitrogen will occur, unless a new supply shall meanwhile have been discovered.
Because of its easy availability, sodium ni trate acts quickly in inducing growth. For this reason it is used much by market gardeners, and for other purposes when a rapid growth is required. It is the most active form of nitro gen, with the possible exception of calcium ni trate. A light dressing on meadow land in
early spring assists greatly in hastening growth by furnishing available nitrogen before the conditions are favorable for making available the more inert nitrogen of the soil. On small grain a similarly useful purpose is served where the soil is not rich.
Owing to the fact that nitrate is not ab sorbed by the soil in large quantities, it is easily lost in the drainage water; for this reason it should be applied only when crops are growing on the soil.
Ammonium When coal is dis tilled a portion of the nitrogen is liberated as ammonia, and is found in the gas and in the ammoniacal liquor which condenses when the gas is cooled. Coal is distilled commercially in coal-gas plants and in by-product coke-oven works, the latter being the larger in tonnage. In either case the ammonia is recovered from the gas by washing it with water or with dilute sulphuric acid. Where water is used ammonia cal liquor is produced, this being a mixture of various ammonia compounds, among them the carbonate, sulphide, hydrosulphide, cyanide, sul phate, sulphate, thio-sulphate and chloride. The first four of them are classed as volatile because they give up their ammonia on boiling, whereas the remaining ones do not. The liquor is treated by steam distillation and the am monia is driven off, the non-volatile portion being freed by adding lime. The ammonia gas then passes to a saturating box where it is bubbled through dilute sulphuric acid and sul phate of ammonia is formed. This is dipped from the box with long-handled copper ladles, drained and dried in a centrifugal, and is then ready to bag for shipment.
Where the washing of the gas is done with sulphuric acid, the sulphate is formed directly, and may be dried and bagged without further treatment. This process requires less appara tus and produces an equally high-grade of product.
Chemically pure sulphate of ammonia con tains 21.2 per cent of nitrogen. The commer cial product contains about 20 per cent of nitro gen. It is the most concentrated form in which nitrogen can be purchased for use as a fertilizer. Its effect on crops is not so rapid as that of sodium nitrate, but it is not so quickly carried from the soil by drainage water, as the ammonium salts are readily absorbed by the soil A pound of nitrogen in the form of am monium sulphate has about the same agricul tural value as the same amount in the form of nitrate of soda if the soil on which it is used is abundantly supplied with lime; but on an acid soil anunonium sulphate has less value.