FURNACE 



3378 



FURNACE 



Furnace (Lat. fornax, a furnace). 

 Term applied to structures in which 

 heat is developed or utilised, in- 

 cluding those used for steam 

 raising and certain chemical opera- 

 tions. Its most general and im- 

 portant application, however, is to 

 the structures used for the extrac- 

 tion of metals from their ores, or for 

 the refining or working of metals. 

 Some reference to the earliest forms 

 of furnaces will be found under the 

 heading Metallurgy. Modern fur- 

 naces may conveniently be divided 

 into five types, each of which again 

 may be sub-divided into classes ; 

 while one type will here and there 

 shade off into another. 



Hearths, the first type, are very 

 largely used for the preliminary 

 metallurgical operation of roasting 

 ores to drive off sulphur, arsenic, or 

 other volatile elements. Such 

 roasting hearths are the simplest 

 forms of furnace, consisting, in 

 some cases, of nothing more than a 

 prepared piece of ground on which 

 the ore is stacked in a pile or heap ; 

 more advanced forms are seen in 

 the stall, pit, and kiln, and in the 

 hearth used for the liquation of 

 argentiferous copper. All these are 

 worked by natural draught. In 

 the common blacksmith's hearth 

 and the iron refinery, we have a type 

 of hearth worked by forced draught. 



The second type of furnace is the 

 shaft, worked by natural or forced 

 draught. Some are in height less, 

 or little more, than in breadth, and 

 in others the height considerably 

 exceeds the breadth or diameter. 

 In the former case we have the 

 iron ore calciner, and various kilns, 

 and in the latter the blast furnace, 

 the cupola and special modifica- 

 tions of the blast furnace, such as 

 the Pilz and the Raschette. 

 The Reverberatory Furnace 



The third type is the reverber- 

 atory, which, while it may be 

 worked either by natural or forced 

 draught, is always distinguished by 

 a particular principle indicated by 

 its title. Whatever metal is being 

 treated in this furnace, it is not 

 normally in contact with solid fuel, 

 but is smelted of treated by causing 

 the heat to reverberate, or to be 

 thrown from the crown or sides of 

 the furnace on to the metal below. 

 There are many forms of this type 

 of furnace, including the puddling 

 and tube furnace, and forms asso- 

 ciated with the names of Siemens, 

 Hasenclever, Bruckner, Pearce, 

 Brown, and Stetefeldt. 



The fourth type may be called 

 the close chamber type, and may 

 be divided into two classes, those 

 in which the material under treat- 

 ment is merely melted more or less, 

 and those in which the substance 

 is volatilised. To the former belong 



the ordinary crucible and muffle 

 furnaces, and to the latter the 

 retort furnaces as used for the pro- 

 duction of zinc. The fifth type is re- 

 presented by the electrical furnace, 

 which like other types assumes 

 various forms, and may have 

 features either of the shaft or 

 reverberatory classes. 



The classification of furnaces 

 which has just been sketched, while 

 not perfect, is perhaps the simplest 

 thai; could be made, 



though an- *f U.^, other useful 

 classifica- aJMf' tion might 

 be arranged H I ' based upon 



exception 

 more ele- 

 forms of 

 furnaces 

 ally con- 

 two es- 



Furnace. Fuinace of closed vessel 

 type, as used for production of steel 

 for cutlery, etc., by cementation pro- 

 cess. A, firegrate; B, furnace ; C C', 

 pots or boxes containing bars of iron 

 in carbonaceous matter ; D, man- 

 hole ; E, shaft ; F, ash-pit 



sential portions, an inner one, 

 which contains the metal, and in 

 some forms the fuel also, and an 

 outer portion, the purpose of 

 which is to give structural stability 

 to the whole. The inner portion 

 may be detached as in the crucible 

 furnace ; but in any case, as it 

 must withstand very high tem- 

 peratures and also it may be the 

 combined mechanical and scouring 

 action of the molten contents, it is 

 necessary to construct it of re- 

 fractory materials. Again, where 

 it is part of the fixed structure, as 

 it must in course of time wear away, 

 it is desirable to build it so that it 

 may be renewed without serious 

 disturbance to the outer structure. 

 It is, therefore, usually made in 

 the form of a removable liner. The 

 materials used in the construction 

 of this important inner section 



comprise alumina, silica, lime, mag- 

 nesia, graphite, in the form of fire- 

 bricks of clay, bauxite, or magnesia 

 or lime, Ganister and Dinas rock, 

 and various special preparations. 



As in most modern furnaces 

 large quantities of materials, ore, 

 fuel, and fluxes require to be 

 handled, much ingenuity has been 

 expended in devising mechanical 

 appliances for this purpose in 

 order to save labour ; while gaseous 

 fuel in the forms of producer and 

 water gas has been largely sub- 

 stituted for solid fuels. See Blast 

 Furnace ; Coke ; Metallurgy ; 

 Smelting; also Boiler, illus. 



ELECTKIC FURNACE. The tem- 

 peratures attainable by gases, 

 liquids, and solids when resisting 

 the passage of an electric current 

 far exceed those of the fuel-fired 

 furnace, and even of the oxy- 

 hydrogen flame, and are ap- 

 proached only by those given by 

 the oxy-acetylene jet and the com- 

 bustion of powdered aluminium. 

 The application of electric heating 

 to metallurgical and chemical pro- 

 cesses on a commercial scale began 

 as recently as the year 1800, but 

 has already yielded most important 

 results. We owe to it the possi- 

 bility of manufacturing in large 

 quantities, at a corresponding low 

 cost, aluminium, carbide of cal- 

 cium, pure calcium, carborundum, 

 caustic soda, phosphorus, sodium, 

 strontium, and other chemicals. 

 In the old-established iron and 

 steel industries the electric furnace 

 is rapidly becoming a dangerous 

 rival to the coal or gas-fired fur- 

 nace, especially for the production 

 of high-grade and alloy steels. 

 Moissan's Electric Furnace 



Moissan, an eminent Frenchman, 

 first embodied the idea of the 

 electric furnace in a practical form. 

 His furnace was made from mas- 

 sive blocks of limestone hollowed 

 out into the form of a crucible, the 

 hollowed parts being lined with 

 magnesia. Two carbon poles were 

 introduced from opposite sides 

 just above the hemispherical 

 bottom where the material to be 

 fused would lie. A powerful electro- 

 magnet was fixed on the outside 

 of the furnace in such a manner 

 that as an arc was established 

 between the two carbon poles it 

 could be deflected down on to the 

 material in the crucible. 



In this furnace a temperature 

 of 3,500 C. (6,332 Fah.) could 

 readily be attained, and many sub- 

 stances which had been supposed 

 to be irreducible could be melted. 

 Moissan succeeded in isolating 

 chromium, manganese, molybde- 

 num, titanium, tungsten, uranium, 

 vanadium, and zirconium. Sir 

 William Siemens made further 



