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ash,in chemistry, solid residue of combustion. The chemical composition of an ash depends on that of the substance burned. Wood ash contains metal carbonates (e.g., potassium carbonate) and oxides formed from metals originally compounded in the wood. Coal ash usually has a high content of minerals and is sometimes contaminated with rock; during combustion the mineral matter may become partially fused, forming cinders or clinker. Bone ash is largely made up of calcium phosphate. Seaweed ash (called kelp or varec) contains sodium carbonate, potassium carbonate, and iodine that can be extracted. Fly ash is very fine ash produced during the combustion of many materials.
ash,in botany, any plant of the genus Fraxinus of the family Oleaceae (oliveolive,
common name for the Oleaceae, a family of trees and shrubs (including climbing forms) of warm temperate climates and of the Old World tropics, especially Asia and the East Indies.
..... Click the link for more information. family), trees and shrubs mainly of north temperate regions. The ashes are characterized by small clusters of greenish flowers and by fruits with long "wings" to aid in wind dispersal. The most valuable of the North American species used for hardwood timber is the white ash (F. americana), ranging from Nova Scotia to Minnesota and Texas. Its strong, durable wood is used for sporting goods, furniture, tool handles, and oars. The bark of the blue ash (F. quadrangulata), which is found from the S Midwest to Oklahoma and Tennessee, yields a blue dye. Both the white ash, blue ash, and other North American species as well as the European ash (F. excelsior) are threatened by the emerald ash borer, a beetle native to Asia whose larvae kill ash trees by boring under the bark and into the wood, cutting off the flow of nutrients. Ash dieback, in which crown dieback and leaf loss results from infection with the fungus Hymenoscyphus fraxineus, also is a threat to the European ash. The Mediterranean flowering ash (F. ornus) is the source of commercial mannamanna
, in the Bible, edible substance provided by God for the people of Israel in the wilderness. In the Book of Exodus it is compared to coriander seed and described as fine, white, and flaky, with the taste of honey and wafer.
..... Click the link for more information. . The name flowering ash is also applied to a shrubby species (F. cuspidata) of the California canyon chaparral and to the fringe tree (genus Chionanthus of the same family) of North America and China. The mountain ashmountain ash,
name for any species of the genus Sorbus of the family Rosaceae (rose family), hardy ornamental trees and shrubs native to the Northern Hemisphere, not related to the true ashes.
..... Click the link for more information. and prickly ashprickly ash,
name for two deciduous shrubs or small trees (Zanthoxylum americanum and Z. clava-herculis) of the family Rutaceae (rue family). They are native to E North America and have prickly twigs and foliage similar to that of the unrelated ash tree.
..... Click the link for more information. are not true ashes. Ashes are classified in the division MagnoliophytaMagnoliophyta
, division of the plant kingdom consisting of those organisms commonly called the flowering plants, or angiosperms. The angiosperms have leaves, stems, and roots, and vascular, or conducting, tissue (xylem and phloem).
..... Click the link for more information. , class Magnoliopsida, order Scrophulariales, family Oleaceae.
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