Page:Encyclopædia Britannica, Ninth Edition, v. 13.djvu/309

 IRON 293 coal burnt to carbon dioxide and water vapour at 20. The heat of combustion of coke and charcoal is somewhat less than this : 1 part by weight of carbon gives out about 8000 units of heat, so that, if the coke contained 7 5 per cent, of ash and no appreciable amount of hydrogen, the heat of combustion (burnt to carbon dioxide) would be about 7400 (see 20). For certain purposes, and more especially for use in the blast furnace, the physical properties of the coke used are important ; when caking coal is coked in furnaces so constructed as to permit of the collection of the products of the decomposition of the coal by heat, a larger yield of coke is obtained than is got when the coking is effected at a higher temperature brought about by the combustion of the volatile matters as fast as they are generated ; but the softer coke obtained in the former way is less suited for smelting iron in the blast furnace than the harder variety obtained by the latter pro cess ; where lofty furnaces are in use, a hard coke that will stand the crushing action of the weight of the superincumbent materials answers better than a softer coke which is disintegrated by the pressure. Moreover, the hard compact form is less readily acted 1145011 by carbon dioxide so as to produce carbon oxide (the carbon of the coke being gasefied) than is the case with the softer form of coke ; accordingly it results that when soft coke is employed in the blast furnace a larger amount of it is requisite per given weight of iron made than would be required were hard coke used instead ; so that the greater yield of soft coke from the coal used in the first instance is counterbalanced, and even more than counterbalanced, by the increased quantity required to do the work of the furnace. Grampian s Furnaces. For various purposes for which fuel is employed, whether for raising steam or producing a more or less oxidizing or reducing flame (e.g., in puddling), a form of ilame-pro- ducer is available obtained by blowing into the furnace a jet of air carrying with it finely ground coal ; for this purpose Crampton employs a mill like an ordinary flour mill with Derbyshire grit stones. The ground coal is placed in a hopper A (tig. 3) con- FIG. 3. Crampton s Mill. taining a sieve B, two agitators C and D stirring up the fine coal under the sieve, and urging it outwards through an opening E, the size of which is controlled by a sliding door F ; from this opening it passes between rollers H and I, the distance between which can be regu lated by a screw L acting on a lever MIST, which adjusts the position of the bearings of the upper and smaller roller ; in this way the feed is perfectly under control ; the agitators cannot force out the coal- dust from the hopper at a greater speed than that regulated by the rollers. The stream of issuing coal-dust falls down a shoot K, a scraper O being provided to prevent adherence to the rollers ; at the bottom of the shoot it is blown away continuously by an air blast, flic shoot delivering the dust into the blast pipe continuously ; the blast remaining the same, the amount of fuel is regulated by the screw and levers ; or, the coal-dust supply being constant, the air blast can be varied. The flame thus produced on kindling the jet of air and coal (suitably proportioned to one another) is smoke less, and perfect combustion is effected with an intensely high tem perature ; for puddling and reheating furnaces, for heat-generating purposes generally, and for steam raising, the arrangement answers admirably (Journ. I. and S. lust,., 1873, 91, and 1874, 384; see 24). Besides coal, coke, and charcoal, various other forms of com bustible matter are used as sources of heat in certain of the opera tions involved in the extraction of iron from its ores. Among these may be mentioned the following. Coal Tar. At the Wyandotte Rolling Mills, Michigan, coal tar has been employed as fuel, being injected into the puddling furnace to be heated by means of a jet of superheated steam, which carries with it a certain amount of atmospheric air, the principle being much the same as that of firing tar-stills with waste naphtha. The steam at a pressure of four atmospheres (tiO It) per inch) is super heated by forcing through a coil in the exit flue of the furnace, whereby it is raised to a red heat, and issues from a ^ or ,V inch nozzle into an opening at the level of what would be the bridge were the ordinary firehole employed, the tar dripping down into the opening, and the air drawn in thereat being impelled onwards by the jet so as to fill the whole furnace with flame. Petroleum. Haw petroleum and the lighter benzoline obtained as a bye product in the manufacture of illuminating and lubricat ing oils have been used in America as fuel applied in much the same way as the above-described. Experiments at Pittsburg indicated that for puddling and steel melting furnaces this fuel answered well, a consumption of a gallon of benzoline used in this way producing the heating effect of several times its weight of coal burnt in the ordinary fire-place. Crude petroleum contains, according to Plagge, Carbon 84-00 per cent. Hydrogen 13-75 Oxygen 2 25 Hence its calculated heat of combustion is about 11,300 per unit weight of substance burnt (i.e., 1 part by weight, on combustion to carbon dioxide and water, will give out heat enough to raise the temperature of 11,300 parts of water 1 C. ), or considerably in excess of that of charcoal and coke ; if burnt to carbon dioxide and steam, the heat evolved by petroleum will be some 6 per cent, less, or 10,600, that of coal being 8300 on an average, as stated above. At the Eaines Iron-Works, Titusville, Pennsylvania, petroleum is allowed to trickle over a series of shelves in a cham ber through which highly superheated steam passes; the current of combustible vapour produced is used for reheating and puddling furnaces, with the result of employing thirty barrels of petroleum daily for an output of iron that would otherwise require 40 tons of coal. Natural Gas. In Pennsylvania the gas evolved from petroleum wells and springs into a subterranean stratum (some 1600 feet below the surface) is largely utilized as fuel. One of the largest of these, the Delamater Well, some 30 miles from Pittsbuvg, was described in 1877 by Professor Laurence Smith as having at first yielded considerable amounts of petroleum, but then giving off nothing but gas coming up with a velocity of 1700 feet per second at the rate of about a million cubic feet per hour, or upwards of 1400 tons daily. In a 5| pipe at the well the pressure was 100 1T&amp;gt; per square inch, so that large engines were worked by the gas current pressure alone. The illuminating power was about 74 candles, or less than half that of good coal gas ; the calorific effect was considerably superior to that of the most bituminous coal (weight for weight) on account of the much larger percentage of hydrogen (free and combined). Puddling and reheating furnaces fired with this fuel fed in through pipes in the rear of the fire bridge answer well, but emit some smoke ; when it is used with a more plentiful supply of air under steam boilers, no smoke at all is produced. The composition of the gas from some of these wells is indicated by the following analyses by Sadtlcr : Burns, Butlur Co. Lucliburg, Westmore land Co. ITarvey, Butler Co. Chfi-rytree. Indiana Co. Ethane. CJL 18 12 4-39 5-72 6 SO Olefines CnH 0-56 Marsh gas CH, 75 44 89-65 80-12 60-27 Hydrogen 6-10 4-79 13-50 22 50 Carbon oxide Carbon dioxide... Nitrogen CO co a trace 0-34 0-26 0-35 0-66 2-21 7-39 Oxvtren 0-83 100-00 100 -CO 100-00 100-00 Gaseous Fuel. Various forms of arrangement for pro ducing combustible gases in one place and leading them by means of tubes elsewhere to be burnt as fuel have been devised by numerous inventors. The object arrived at being essentially cheapness of production, the combustible substances have usually been coal, slack, lignites, shales, and the like, more or less submitted to distillation by the heat developed by the combustion of a part of the mass, the ultimate product of this combustion being largely carbon oxide formed by the action of the heated carbonaceous