« السابقةمتابعة »
ress, becomes the property of the owner of the land to which it is added, whether it be due to alluvion, the deposit of sand and soil by the action of the tides, the washing of waves or the current of a stream, or by reliction, the gradual withdrawal or drying up of a watercourse. For the aorresponding principle in the law of personal property, see Accession. Accrlngton (anc. Akcringlon), England, a munic. bor., Lancashire, 23 m. N. of Manchester. Cotton-spinning, weaving, calicoprinting, and manufacture of textile machinery In the district are coal mines and quarries. Pop. (1901) 43.095.
Accumulations. Funds accruing from lime to time under a trust created for the purpose of increasing the principal fund through the periodical addition of the income thereof. The validity of provisions for accumulation are primarily determined by the rule against perpetuities, which restricts the vesting of future interests in property to the period of lives in being and twenty-one years. But the policy of the law is unfavorable to accumulations for long periods of time and the rule governing such trusts has consequently been changed so as to limit trie period usually to twentyone years. This was effected in England by the Thellusson Act, passed in 1800, and in the several United States by similar statutes. Accumulator, Heat, has for its purpose the accumulation of heat delivered continuously so that it may be expended during short intervals, or, on the other hand, the storing of heat delivered intermittently so that it may be available for continuous use. In engineering practice the heat storing medium is usually water which is not only generally available, but has the highest specific heat per unit of weight of all common substances, and readily transfers its heat to or absorbs it from steam by evaporation or condensation of the latter.
An example of accumulators of the first class is found in special heat storage boilers adapted to receive steam at high pressure from steam boilers operated continuously and then to give off steam during short periods of great demand, as during the rush hours in electric traction power plants. The steam pressure carried in the accumulator, which is simply a large and strong steel tank, must be considerably higher than the working power of the engines, as it is only Dy allowing the pressure and therefore the temperature of the mass of water in the heat storage tank to fall that the latter is able to supply heal and steam. For instance, if the working pressure of the engines is 150 pounds
per sq. in., corresponding to a steam temperature of 365.6° F., the maximum pressure in the accumulators may be 300 pounds per sq. in., corresponding to a temperature of 421.8° F. During the period of withdrawal, steam will Dc allowed to flow from the storage tanks through a pressure reducing valve and each one hundred pounds of water in the storage tank will be capable of giving up 56 heat units in cooling 421.8* to 365.6° F., and further of evaporating .07 Ib. of steam. During the period of charging the boilers are in free communication with the accumulator, but during the period of discharge of the accumulator the boilers supply steam directly to the engines. This class of heat accumulator has found only limited application, chiefly in Europe. The advantages claimed for it arc that it enables a large maximum load to be carried by a moderate-sized equipment of boilers, and that it permits the boilers to be operated at a uniform and efficient rating throughout the day. The obvious disadvantage is the extra cost of apparatus, which might conceivably overbalance the advantages. The other type of heat accumulator, in which heat from an intermittent source is stored for continuous use, is found in lowpressure steam turbine practice. Take for instance, steel mills, where large volumes of steam are exhausted^ at irregular intervals by powerful engines used for driving the rolls or in collerics where the same is true of the winding engines. A steam turbine receiving this steam from the engines at atmospheric pressure and exhausting into a high vacuum produced by a condenser will generate, roughly, about as much more power as has already been produced in the main engine. As steam turbines are, as a rule, employed to drive electric generators ana must run constantly, it therefore becomes necessary to store the steam and heat exhausted by the main engine. This is accomplished by the following methods: first, by directing the exhaust steam into large chambers or tanks filled with scrap iron, as old rails, etc.; second, by directing the steam into a chamber filled with a multitude of small trays, each containing water; third, uy blowing the exhaust steam in under the surface of water contained in suitable closed tanksj fourth, by directing the steam into a tank above a large body of water, and by mechanical means, throwing tne water up into the steam. In all four methods, as will be noted, the object aimed at is to bring the exhaust steam into intimate contact with the whole mass of water or other material which is to store
the heat. If the steam be directed merely into a closed tank above the water, it will be effective in heating only the upper surface of water. In order to prevent dangerous accumulations of pressure in the heat accumulator, a direct connection to the atmosphere is usually provided through a "back
Sressure" valve. On the other and to supply steam continuously to the turbine in case the main engine should be shut off for an exceptionally long time, a pressurereducing valve admitting live steam from the boilers is necessary. Supposing the back pressure valve De set to open at ten pounds above atmospheric pressure and the reducing valve to begin admitting live steam at three pounds below atmospheric pressure, we have a total pressure range of thirteen pounds and a temperature range of 3S° F. Under these conditions one pound of water in the accumulator is capable of condensing .04 pound of exhaust steam, thereby storing 29 heat units, and of giving up equal quantities of steam andneat wncn the pressure falls again.
Accumulator, Hydraulic, devised by Lord Armstrong, receives power at a constant rate from a hydraulic pump, and gives it out in large quantities at a time to machines, such as cranes, which work intermittently. It is thus a means of obtaining a considerable volume of water under a high head. It consists of a vertical cylinder with a heavily-weighted ram. See Barr's Pumping Machinery; and Hydraulic MaChinery.
Accumulators, Electric, or Secondary Batteries. When an electric battery is discharged, there occur chemical changes in the liquids and electrodes, caused by the passage of the currents through the cell. In some forms of cell all the products of the charge remain in the cell, and the passage of a current in the reverse direction will produce the reverse action and restore the original conditions. Broadly speaking, the current causes a transference of oxygen to one pole and hydrogen to the other, both being brought back to their previous positions and combinations by the reverse current. Such a battery acts as a reservoir or accumulator of electric energy; for, after each discharge, electric energy is again stored in it by driving a reverse current through it from some other source of electric energy. In the process of charging, the electric pressure of the cell must be overcome, and the resistance of the cell absorbs additional pressure. On discharging, there is likewise a loss of pressure, due to the resistance of the cell, and the
conditions the loss is not more than some five per cent.
Tlu-orv o/ Cell.—Though m.inv forms of battery allow of reversal, there are few which are satisfactory. The simple collection of oxygen and hvdrogen at the poles is impracticable, since they pass off as gases, and the only b'attery that has proved satisfactory is the lead battery invented by Planl6. In this a plate of pure lead forms the negative and a plate of peroxide of lead the positive electrode, immersed in sulphuric arid and water. On discharging, the lead is converted into sulphate of lead, and the hydrogen conveyed to the positive plate is oxiili/.ed by the peroxide of lead. The lower oxide thus formed is attacked bv the acid, so that sulphate of lead is produced on both plates, and a part of the acid is removed from the liquid. On reversing the current hydrogen is carried to the negative plate, and reduces the sulphate of lead back to metallic lead, while the oxygen converts the sulphate on
cceds, and its strength indicates the state of the reservoir.
The action of the cell is similar to that of an ordinary primary battery, but there arc important differences. By the use of lead instead of zinc there is formed the insoluble lead sulphate in place of the soluble zinc sulphate or chloride. Therefore the surface becomes covered with the products of the action on both electrodes, and the interior parts of the plates arc rendered useless. Consequently both negative and positive plates arc constructed of porous, spongy material, presenting an enormous surface to the acid, and solid metal is used only as a framework or carrier. So long as any portion of unchanged material remains in contact with the acid, the r.M.v. is maintained with very gradual reduction. Fi;». 2 shows a typical curve of discharge in which horizontal distances represent ampere hours. The cell is practically discharged at 1.8 volts. On charging Fig. 1, the E.M.F. rises rapidly to nearly
2.1 volts, then more slowly to 2.5 volts.
Construction of Plates.—The essential construction is a framework of lead, or an alloy of lead and antimony, containing spongy material. Many forms of grid are in use. The negative plate is now usually a thin skeleton of lend forming many small pockets, into which is pressed a paste of lead oxide and sulphuric acid. On reduction by the current, this forms a porous mass of lead. The frame of the positive plate is made more stoutly, since the oxygen produced at the end of everv charge corrodes the frame slowly. It may be made by filling pockets or grooves with paste as before, which are then converted into peroxide; or this rr.av be produced directly by repeated charging, assisted 'by oxidizing materials, such as sodmm nitrate.
Capacity.—The capacity of a cell is determined by the Quantity of electricity it'will deliver, usually reckoned in ampere hours. It depends on the construction and size of the plates; but instead of using very large plates, several of cacri kind mav be used, with positive and negative placed alternately. All of one kind are connected to a common bar, which forms the terminal of the cill. The capacity is not a constant quantity, for with a large current the acid in the pores of the plate is so rapidly weakened that fresh acid from outside cannot diffuse into the plate sufficiently quickly. Hence the interior portions arc not fully discharged, unless the cell is given a period of rest.
Arrangement of Cell.—The alternate positive and negative plates are held about half an inch apart by strips of glass or ebonite, and tne whole is clamped together to prevent deformation of the plates. The space allows any loosened material to fall clear to the bottom, and in a large battery some three inches of space arc left below the plates for its reception. The acid is specially prepared, free from metals, with a density of 1.2, or one volume of strong acid to five of water. If too strong, the lead is slowly attacked; while if too weak, the E.m.f. of the cell is reduced. At this strength also the resistance of the acid is at a minimum. The plates are usually contained in glass boxes when the size is moderate, but for large central-station cells lead-lined wooden boxes, or boxes of a lead alloy, are used. Ebonite boxes are employed for the cells of automobile vehicles on account of lightness, while small portable batteries are generally put in leadlined wood or ebonite with wooden case. The boxes are supported on glass or porcelain feet to insulate them from the ground, and these Aceldama
should be wiped clean periodically.
Method of Charging.—It is usual to charge the cells with a definite current depending on the size of the cells; and if this current is exceeded at the end of the charge, the rapid evolution of gas tends to dislodge portions of the active material, especially on the positive plate, and these portions are lost. But rapid charging at the commencement produces no ill effects, and is often adopted to save time; while a reduction of current towards the end favors the complete conversion of the interior parts without great evolution of gas. Too rapid charging and discharging are apt to produce buckling of the plates, since the processes cause a change of bulk of the material, and more separators are required to prevent this.
The efficiency of the cell, or the relation between energy taken out and energy put in, depends on the care bestowed on the cells. In central stations, with frequent small discharges and charges, it may reach 80 per cent., but 70 per cent, is more usual; while in motor cars 55 or 60 per cent, is not uncommon, a high current and overcharging being the cause of the low efficiency.
Care oj Cells—-Batteries deteriorate but little if they are not discharged to the full extent, and are charged immediately after discharge. But if allowed to stand for some time after a discharge, the plates are rapidly attacked by the acid, with the formation of white sulphate of lead. This is difficult to convert, and the material thus 'sulphated' is apt to split off and be lost. The life may be anything from six months to ten years, according to treatment. Frequent exhaustion, heavy currents, and leaving uncharged shorten the life. When worn out, new plates can be inserted at about half the cost of the original battery.
The water slowly evaporates, and distilled or rain water is added as soon as the tops of the plates emerge. Hard water produces a skin on the plates. Fresh acid is rarely needed. If a cell shows a loss of E.m.f., it is probably due to a piece of active material bridging across between the piates and allowing a leakage of current. A slip of wood passed between the plates is the remedy, and a long charge. It will be found that when gas is evolved from the cells a fine mist of acid rises, and the room must be well ventilated. Also all metal and woodwork should be kept well painted, to prevent corrosion.
Sets of Cells.—Batteries are usually required for a system of constant E.M.F., and the number
and the efficiency is about 60 per cent., but the durability appears to be superior to that of the lead cell. See Wade's Secondary Batteries, Niblett's Storage Batteries, Treadwell's Storage Batteries, ana Slingo and Brooker's Electrical Engineering, and the current electrical journals and Proceedings of the American.Institute of Electrical Engineers.
Aceldama (Aram. 'the field of blood'), so named either because it was bought with the money with which Judas had been bribed (Matt. 27: 7, 8), or because it was the scene of the traitor's tragic death (Acts 1: 18. 19). It is traditionally identified with Hakked-Dumm, near the Pool of Siloam, to the s. of Jerusalem. For description see Schick, Pal. Ex. Fund Quarterly Reports, 1892, pp.283;?.
Acer, Acerace/e. See Maple.
Acernus, Sebastian Fabian (1551-1608), the Latinized name of a Polish poet (Klonowicz), surnamed the Sarmatian Ovid. He wrote Victoria Dcorum, a satire on the Polish nobility; the epic poem Flis; a Latin eulogium of Red Russia in Roxolania; etc.
Acerra (anc. Accrrae), tn., Italy, and episc. see, prov. Caserta, 9 m. N.E. of Naples: has sulphur springs, and a cathedral rebuilt in 1788 alter an earthquake. Pop. (1901) 16,397.
Acetabulum (Lat. acctum, 'vinegar'), an ancient Roman sauce-vessel; thence an ancient liquid measure, about half a gill. The word is applied in anatomy to the cup-shaped articular surface of the innominate bone which receives the head of the femur. also to other cuplike structures in animals and fungi.
Acetamldf (CHjCO.NHj) is a white crystalline solid prepared by the action of ethyl acetate on ammonia. It melts "at 83° c., bcils at 222° C., is easilv soluble in water, and when heated with acids or alkalis is converted into ammonia and acetic acid, or their salts.
Acctanlllde. See Antifebrin.
Acotlc Acid (CH.CO.OH} is formed by the oxidation of alcohol, and is thus present in vinegar. It is chiefly prepared by the
destructive distillation of wood (hence called 'pvroligneousacid'), and is purified from the ether obtained products by neutralization with hmc and subsequent distillation of resulting calcium acetate with sulphuric acid. Acetic acid is a colorless liquid which boils at 118° c., and solidifies, when pure, at about 1">° c. into a crystalline solid known as 'glacial acetic acid.' It is of sp. cr. 1.056 at 15° c. It is very stable, and acts as a monobasic acid, forming a series of sails called acetates, among which are those of calcium, sodium, lead, iron, and
aluminium. These are obtained by dissolving the metallic oxide, hydroxide, or carbonate in the acid. They are soluble in water, and decomposed by heat, giving, as a rule, acetone and a carbonate. From this property calcium acetate is largely usea as a source of acetone: ana from the ease with which the acetates of aluminium, iron, etc., are decomposed by water-vapor into insoluble hydroxides and acetic acid, these bodies are extensively employed as mordants in dyeing. Basic acetate of copper, or verdigris, and aceto-arsenitc of copper, or Schweinfurther or Paris green, are used as pigments, lead acetate for the preparation of chrome yellow, and the alkali acetates to a small extent in medicine. Acetic acid itself is used as a solvent for gelatin, albumin, resins, oils, etc., for the preparation of the acetates, and in medicine both externally and internally. The strong acid is used externally as a caustic, the 6 and 36 per cent, acids arc used in medicine: the very dilute acid is spongea over the body as a refrigerant in fevers. Internally it has the common action of acids, acting as an escharotic, irritant, or stimulant in the mouth or stomach.
Aeetlc Ether (ethyl acetate. CHjCO.O.C,H,, prepared by the action of sodium acetate and sulphuric acid on alcohol) is a colorless liquid with a refreshing, penetrating smell. It is used in medicine as a stimulant, also as a solvent and flavoring agent.
A e e t o n e (dimethyl ketone, CHjCO.CH,) is the simplest of the class of substances called ketones. It is present in the products of the destructive distillation of wood, but is mainly prepared by heating calcium acclate. Acetone is a colorless, volatile liquid of boiling point 56.5° c. and sp. gr. .79 at 20° c., with a peculiar empyreumatic odor. It mixes with water and alcohol, and acts as a useful solvent. It is also cmployed in the preparation of chloroform, iodoform, and sulphonal, as well as for denaturing or rendering unpalatable ethyl alcohol.
Acetophenone, Hypnone (phenyl-methyl-kctone,C.Il5CO.CH,), ayellowish,oily fluid which boils at 198-200° c., of sp. gr. 1.0285 (15° C.). Crvstalline at low temperature. Used as hypnotic in coses of 5 grains. When taken in large doses it causes coma and death.
Acetyl (CH,CO) is a univalent radical of which acetic acid, acetyl chloride, etc., are derivatives, the former being the hydroxide, and the latter the chloride.
Acetylene (C,H,) is a colorless, brilliant gas, having a faint odor of garlic. Discovered by
Berthelot (1862), it was first brought into commercial use by Willson's discovery (1888) of the modern method of preparing calcium carbid_e, and is now widely used as an illuminant. It occurs in small quantities in coal gas, and to a greater extent in oil gas. Acetylene can be obtained by forming an arc between carbon poles in an atmosphere of hydrogen, or by the imperfect combustion of coal gas, but is usually prepared by bringing water into contact wfth calcium carbide, which is a crystalline substance obtained by strongly heating a mixture of lime an'd powdered coke in the electric furnace. Carbide is now manufactured on a large scale in America and Europe, chiefly by means of waterpower—eg. Niagara Falls, Sault Rapids, Falls of Foyers, Sarpsborg —and is supplied to consumers in air-tight drums. It must be kept hermetically sealed from the atmosphere, because it rapidly takes up moisture, thus deteriorating in quality and liberating the gas. Theoretically, 1 Ib. of carbide yields 5.8 cub. ft. of gas, but the commercial substance rarely yields more than 4.5 cub. ft. The specific gravity of acetylene is about twice that of coal gas. The presence of impurities especially compounds of phosphorus and sulphur, often gives it a very powerful and unpleasant odor, which is erroneously ascribed to the gas itself. It is liable to spontaneous explosion when compressed into the liquid state, and it is now illegal to manufacture or keep it in this form. At a pressure of 100 inches of water, or less, it is officially regarded as safe. In contact with copper, acetylene forms a dangerous detonating compound; its action on wet blcachingpowder, sometimes used as a purifying medium, has led to explosions; and its general chemical reactions have not been fully investigated. The gas is prepared in generators, in which water and carbide are brought together in various ways. The best form is that in which the carbide is thrown into an excess of water, for when water is dropped upon carbide intense heat is generated, and the gas is partly transformed into oily compounds, which condense in the pipes. From the generator the gas should be led into a separate gas-holder, large enough to contain a supply for twenty-four hours, ami weighted to give a pressure of 3 inches of water; thence through a purifier, in which the gas is exposed to a large surface of dry bleaching-powder. or is passed through sulphuric acid to the main pipes. Taps must be well ground in t*vnd lubricated with vaseline, as the gas corrcdes brass work. Special burners, by which
two jets of flame are thrown against each other, are used. The flame is intensely white. When examined by the spectroscope it is found to resemble sunlight more nearly than any other artificial illuminant. By the use of suitably tinted globes it is possible to produce a light which gives the true colors of objects; but the naked acetylene flame, though better in this respect than lamp, coal gas, or electric light, still confuses some blues and greens. Its extreme whiteness makes the light somewhat trying to the eyes. Acetylene has been used successfully for bicycle lamps, dock lights, and launch searchlights, and for church and domestic illumination in country places. The burners ordinarily used in house-lighting, consuming .7 cub. ft. per hour, give from 16 to 20 candles. The cost of lighting by acetylene is about the same as lighting by coal gas at 75 cts. per 1.000 ft. The gas is sometimes added to coal gas and oil gas to increase their luminosity: and it is an expensive but powerful heating agent for gas motors and bunsen burners. See Gibb's Acetylene (1900).
Achael, Acheaeans, a name applied by Homer to the whole of the Greek nation, and so used also by later poets. It probably represents the population of Greece before the admixture of races caused by the Dorian invasion. In historical times the name is restricted to the inhabitants of the north coast of the Peloponnesus (Achaia), who were united in a league of twelve towns, which after 251 B.c. became the chief power of Greece. Its constitution was to some extent based on representation. Finally the league declared war against the Romans, and was crushed by them in 146 B.C.
Achsemenlans, a dynasty of ancient Persia; it occupied the throne from about 730 B.C. to 333 B.C., and counted among its kings Cyrus the Great, Cambyses, and Darius the Great. In old Persian inscriptions Darius proudly traces his lineage back to Achtemenes, the founder of the line.
Achaia. (1.) With Elis, prpv. (nomarchy) of Greece, extending from E. to w. along s. side of G. of Corinth; mountainous; coast lowchief currant-producing region of mainland. Area, 2,028 sq. m. Pop. (1806) 236,251. Chief tn. and port, Patras. (3.) In New Testament times the s. prov. of Greece, the N. being Macedonia. Gallio was Roman 'deputy' or proconsul of Achaia (Acts 18:12). Aehamoth, or Acamoth. the (Valentinian) Gnostic name for a lower or imperfect manifestation of Wisdom, mother of the Demiurge" the form in which spirit becomes subservient to matter,