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ash, in botany
ash, in chemistry
an incombustible residue that is formed by the inorganic impurities in fuel after its complete combustion. The ash content of coal and lignite is 1–45 percent or more; that of combustible shales, 50–80 percent; that of fuel peat, 2–30 percent; that of firewood, usually less than 1 percent; that of other kinds of plant fuels, 3–5 percent; and that of mazut, usually up to 0.15 percent, but sometimes higher. The upper limit of the inorganic impurity content determines the technological possibility and economic feasibility of using a particular mineral as a fuel.
The presence of ash reduces the relative amount of combustibles in a fuel. Upon combustion of a fuel, part of the heat is lost with the ash. In boiler installations molten ash is deposited on the tubes of the furnace baffles, shields, and other parts as a sintered slag. The deposition of ash on heating surfaces inhibits the transfer of heat from furnace gases to the water or stem and increases the boiler’s aerodynamic resistance. Fly ash abrades boiler tubes and flue gas pumps, and ash pollutes the air when it is carried away with the flue gases.
In the building-materials industry ashes are used for making certain kinds of concrete. Rare and trace elements, such as germanium and gallium, are extracted from the ash of certain coals.
In agriculture, ash is widely used as a fertilizer containing potassium in the form of potash (K2CO3), which is readily soluble in water and available to plants. Other inorganic substances that are essential for plants (phosphorus, calcium, magnesium, sulfur, boron, and manganese); as well as other macroelements and trace elements, are present in ash. The high calcium carbonate content of shale and peat ash makes possible their use to reduce soil acidity. The average percentages in ash of compounds containing the main nutritive elements of plants are given in Table 1.
|Table 1. Content of inorganic substances in ash used as fertilizer (percent)|
|Potassium (K,0)||Phosphorus (P,0)||Calcium (CaO)|
Ash is added to all soils and crops, but its use is most expedient with tobacco, potatoes, buckwheat, leguminous plants, flax, and fruit crops. It is introduced with the plowing, when turning over the soil under the crowns of trees (4–15 centners per hectare), and in planting potatoes, cabbage, and tomatoes (3–5 centners per hectare), as well as to fertilize meadows and cultivated and grain crops (3–5 centners per hectare). Ash must not be mixed with organic and ammonia fertilizers (to avoid loss of ammonia) or with superphosphate and other water-soluble phosphorus fertilizers (it causes retrogradation, reducing the ability of plants to assimilate phosphates).
REFERENCESAgrokhimiia. Edited by V. M. Klechkovskii and A. V. Peterburgskii. Moscow, 1967.
Khimizatsiia sel’skogo khoziaistva: Nauchno-tekhnicheskii slovar’-spravochnik, 2nd ed. Edited by L. L. Balashev and S. I. VoPfkovich. Moscow, 1968.
A. V. PETERBURGSKII
Ash runs under 386BSD, NetBSD, FreeBSD, and Linux.
FTP Linux version.