Page:Encyclopædia Britannica, Ninth Edition, v. 13.djvu/308

IKON with three firing grates, two on one side and one on the other. The magnetic ores and quartzose haematites of Sweden, Russia, America, and elsewhere are often calcined in Westmann s kiln (tig. 2). This is a nearly tubular vertical kiln slightly diminishing in diameter upwards, and fed at the base with waste gases from the blast furnace, together with air for their combustion ; the ore is thus rendered somewhat less dense than at first, whilst pyrites, when present, is decomposed ; analogous arrangements are employed in many Continental iron-works. Many attempts have been made to smelt clay ironstone without previous calcination, but as a general - rule but little saving appears to be effected, if indeed any at all is brought about ; the value of the small coal and slack saved in the roasting barely, if at all, compensates for various practical disadvan tages attending the use of raw ore as compared with calcined ores. Much the same remarks apply to brown ores, especially when earthy. Several methods have been proposed to remove phosphorus com pounds from ores containing that constituent before smelting them, so as to produce a purer metal ; the success of these as manufacturing operations, however, has been mostly indifferent, the cost and labour involved not being adequately repaid by the results. Amongst these processes may be noticed those of Jacobi and Velge ; the former places the broken-up ores in tanks, and lixiviates them with aqueous solution of sulphurous acid obtained by burning pyrites ; in this way phosphates are dissolved out, from which manures may be made ; the latter impregnates the ores (previously calcined) with brine, and after drying calcines again, subsequently washing out the phosphate of sodium produced by water, or preferably water containing a little hydrochloric acid. Jacobi s process has been tried on a considerable scale, and apparently could be worked com mercially were it not that, to extract the phosphates thoroughly, the ore requires crushing to coarse powder, or at least to lumps so small as very materially to interfere with its employment in the blast furnace ; moreover, whilst calcium phosphate is readily soluble in solution of sulphurous acid, ferrous phosphate is not soluble in that menstruum, and hence is not removed from ores containing phos phorus in this form. The ores being ready for smelting, the next stage in their treat ment consists in subjecting them to the reducing action of carbon oxide (and also of carbon), at a temperature gradually increasing as the reduction goes on, until finally the reduced metal melts ; in order to promote the separation of the earthy impurities of the ore from, the metal, and to facilitate their fusion, it is requisite either to mix various classes of ores together in such a fashion that the silicious admixtures of the one and the calcareous and aluminous impurities of the others may jointly be in suitable proportions relatively to one another ; or, which is usually more convenient, to add calcareous or other matters (in the form of limestone, ferruginous clay, aluminous poor iron ores, &c. ) to serve as a flux. To carry out this operation the blast furnace is employed, the ore, flux, and fuel being charged in at the top of the erection, and air being blown in at the base, so that a mixture of carbon oxide and nitrogen is formed at the lower levels, which, passing upwards, effects the deoxidation of the ore ; the heat produced at the base fuses the reduced iron and the earthy matters, &c. , which accumu late in two layers (the former being the heavier), and are drawn off from time to time, the one as cast or pig iron, into moulds for the market, the other as cinder or slag, usually of little or no value. Fresh materials are added at the top, so that the furnace works continuously. 10. Fuel. The fuel employed in iron smelting by means of the blast furnace is substantially always one of. three kinds, viz., raw coal (anthracitic, or more or less bitu minous), coke, or charcoal ; l inasmuch, however, as raw coal inserted into the mouth of a blast furnace speedily becomes coked, the combustible matter reaching the tuyere level is invariably carbon in a greater or less state of purity. The effect of using raw coal instead of coke in the first instance is chiefly marked as regards the alteration thereby produced in the character of the gases in the upper part of the furnace, and the consequent alteration in the chemical changes taking place, chiefly owing to the presence of hydrogen and hydrocarbons in much larger proportion. For numerous other operations in connexion with the metal lurgy of iron, other kinds of fuel are often employed, lignites, turf, wood, <fec. The following analyses will give 1 Peat lias been used successfully as fuel in some Austrian furnaces, especially in the Vordernberg district, in open-topped furnaces about 30 feet high. The peat was made into compressed balls and dried in the air ; these descended to the tuyere without losing their shape, but of course wholly carbonized. The iron produced was white, but of as good quality as that obtained with charcoal. Lignites and brown coal have similarly been employed in districts where better coals are scarce. an idea of the general character of the fuels usually employed. In the north of England a very hard variety of coke, often known as " Durham coke," is made specially for iron smelters ; during the production of this, on an average about one half of the sulphur originally present in the raw coal is expelled, the yield of coke being about two-thirds of the coal employed. Character of ( Coal and-: Locality.... ( Durham CoaU Average. Dowlais Non- caking, poor in Oxygen. South Stafford shire Non- caking, rich in Oxygen. Alais, France. Caking Coa.. 2 Anthra cite, Swansea. Lanca shire Coals. 3 Alder Rilcy. Regn^ult. Hegnault. Admiralty Wright. 82 5 88-13 78-57 89-27 92 -5 (i 77-53 Hydrogen 5-0 4 51 5-29 4 85 3-24 5-32 Oxygen 5-0 2-94 12-88 ) (9-53 Nitrogen 1-0 1-41 1-84 ( 4-47 2-53 -h-30 Sulphur (total) ... Ash 1-2 1-01 2 00 0-39 1-03 ) 1-41 158 h-44 4 -88 1000 100-00 100-00 100-00 100-00 100-00 Sulphur in ash.... 0-05 1 " Busty " and " Brock-well " seams, largely used for making blast furnace coke. 2 Yields a good blast furnace coke. 3 Average of 28 samples of various kinds. Character of Fuel and Locality Bovey Tracey Lignite, Devon shire. Dart moor Peat. Oak Wood. 1 Highly Burnt Black Aider Char coal. 4 Coke from Durham and Noi th- umberland Caking Coal. 3 Haul Coke used in Cleveland Distiict for blast Furnaces. Yaux. Chevan- Violctte. Alder Lowt Irian dier. G6-31 54-02 50-69 96-51 92 5 93-5 5-63 5-21 6-03 0-C2 05 0-4 Oxygen 22-SG 28-18 42-00 57 2-30 1-28 j- 0-93 1 ... 2-36 0-56 1-0 Ash ... 2-27 9-73 1-94 5-0 G-G 100-00 100-00 100-00 100-00 100-0 100-5 1 Exclusive of 2 04 per cent, of ash. 2 Heated to an intense white heat to expel as much volatile matters as possible; similar charcoal prepared at somewhat lower temperatures retained 10 to 15 per cent, of oxygen and hydrogen jointly. 3 Average coke from " Busty " and " Brockwell" seams of coal, specially pre pared for blast furnaces. It is somewhat difficult to fix on an average value for the heat of combustion of coal, great variations being observ able with different classes. The following values of Sclieurer Kestner and Meunier (Annales de Chim. et Phys. [4], 21, 436, and 26, 80) are calculated after allowing for ash, and on the supposition that the carbon dioxide and water produced were formed at the ordinary temperature, near 20: Character of Coal. Percentage Composition. Calorific Value. Carbon. Hydro gen. Oxygen and Nitrogen. Lignites from Basses- Alpes... ] Non-caking coal, Creusot Cakin"- do. do 66-31 70-57 9079 88-48 87-02 92-36 83-82 76-87 88-59 4-85 5-44 4-24 4-41 472 3-66 4-60 4-68 4-69 28-84 23-99 4-97 7-11 8-26 3-98 11-58 18 45 672 6991 7363 9293 9622 9111 9456 8724 8215 9120 .-, ., Blsinzv... Anthracite n , */ (Jreusot Saarbriick coals s Ronchamp coal, average Hence average true coal may be taken to have a heat of combustion of 9000 when ash free ; assuming it to con tain 5 per cent, of ash, 8550 will be the heat produced. If aqueous vapour at 20 were formed instead of liquid water, assuming average coal to yield 40 per cent, of aqueous vapour on complete combustion, 4x593 = 237 heat units less would be evolved, 593 being the latent heat of water at 20 (Regnault) ; so that 8300 may be taken as an approximation to the heat of combustion of ordinary