IRON. 



309 



lion- The preliminary experiments above mentioned, should 

 "V ^ always be made previous to any chiwge in the coal or the 

 iron ore, as the earthy matter in the former is very dif- 

 ferent in different lutis and sometime* even in differ- 

 ent parts of the same bed. The argillaceous iron stone 

 also varies in the proportion of its clay, and sometimes 

 contains a considerable portion of (ilex, which, when it 

 bears a certain proportion to the clay and lime, is r.i-ily 

 separatol Tlit- iron stone abounding with shells, fre- 

 quently contains carbonate of lime, and will require 

 less lime to be added as a flux. 



Formerly, the fuel employed in blast furnaces was 

 charcoal, which is still used on the continent The 

 iron works of this country, with a few exceptions, are 

 carried on with-the coke of pit coal, which is found to 

 be much better fitted for making cast iron. 

 H-v ; .-n The coke is prepared, by piling heaps of coal on the 

 UK coke, ground in the open air. In some works, a short brick 

 llhilsHii jr is placed in the middle of the pile*, which 

 baring holes round the bottom, has the effect ot 

 cing a current of air through the mim of coal* on fire, 

 and bringing them Mpnw into a ?tau- of combustion. 

 In any part of the pile where the combustion is too ra- 

 pid, a quan'ity of ashes are thrown from time to time, 

 without which the carbonaceous part of the coal would 

 become destroyed. Indeed, the operation of coking is 

 intended to dissipate the volatile part merely. As tin's 

 change is effected, the finished part i covered with 

 ah, and ultimately the whole combustion is (topped. 

 The covering is to be kept upon them, till they are 

 cooled below ignition. This coke, when cold and se- 

 parated from the dust, is in the state to be used in the 

 furnace. 



HOTuion The preparation of the iron itone is the next process, 

 the if OQ. which consists in roasting it, for the purpose of separa- 

 ting its volatile matter. For this purpose, the stone is 

 stratified with small coal, in a manner similar to that 



tused in burning lime. These alternate strata are gene- 

 rally exposed to the open air, and the mass allowed to 

 till all the fuel is exhausted. In some iron works, 

 kilns, similar to the lime kiln, have been employed for 



purpose. 



During this process, camphor, carbonic acid, and 

 water are separated. The stone assumes a reddish pur- 

 ple colour, and consists of the pure oxide of iron and 

 earthy matter, principally clay. 1'he limestone, which 

 is employed as the flux, reqqpes no preparsvon ej 

 being broken into pieces. 



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I Hsu !ur - 



In the practical management of a blast furnace, the 

 coke is in general made a constant quantity, the pro- 

 portions of ore and limestone varying with the (| 

 of iron to be made, the season of the year, and the work- 

 ing order of the furnace. The proportions of the ore 

 limestone, will be pretty marly the same at all 

 times when the ore is the same. To give the prsflbe 

 proportions of eat., would not apply generally, and cut 

 merely answer for the iron work from which our state- 

 ment has been taken. The ore is argillaceous, and con- 

 tains on the average about '/7 pc* cent - of iron- 



The liim -tone is that abounding with shcllf, from 



ythire. The coal is rather soft, but not 



very <. and contains a large proportion of 



carbon. The furnace is that described under this ar- 



which, it it common rate of working, makes 



4 iron weekly. The blowing cy- 



-char^c I j ' times in a minute, and coi 



abOfet 100 cubic feet. Hence the ahr discharged in that 



time is 2301) cubic fret. The diameter of the nose-pipe 



i* generally 2f inches. 



At this, and most other blast furnaces, the metal is Iron. 

 run out twice in the 2+ hours, at intervals of 12 hours ^^TT 

 each. The latter periods are called shifts, from the manags . 

 workmen being changed, as the furnace is attended mem O f 

 night and day. During the 12 -hours, 50 charges of blast fur. 

 coke are used, at regular intervals, each charge weigh- naess. 

 ing 2| cwts. During the same period, about the same 

 quantity of calcined ore is added, at similar inter- 

 vals. These are the proportions for the common melt- 

 ing iron, called No. 2. For No. 3, which has less car- 

 bon, and is called forge pig, the coke to the calcined 

 ore is about 6 to 7. That of the best quality, called 

 No. I, and which contains the most carlwn, requires 

 less ore to the coke than No. 2. The limestone is also 

 added at stated intervals ; the whole quantity in the 

 lii hours being in proportion to the coke, as 4 to 11. 



These proportions cannot be applied generally, so 



uiuch depends on the nature of the materials, and other 



circumstance- ; some furnaces work to such a disadvan- 



tage, as to consume a quantity of coke equal to that 



-tated, and yet will not admit of more ore than 



will pro.hu-c from 1'J to 20 tons of iron weekly. Some 



of the Welsh furnaces, on the contrary, will carry so 



much burden, that they witt bear the use of so much 



ore, a* to give from 60 to 75 tons weekly. These 



great differences are dependent upon so many circum- 



stances, as frequently to baffle the skill of the most 



flBperieaoed iron raa-ur-i. I.\p. ri.mv and strict ob- 



un are very essential points in iron-making : but 



.-, mechanical as well as clu-mic il, much facili- 



tates the progress of this useful branch of manufacture. 



We have before attended to these stages of the pro- 

 cess, between the entrance of the materials into the fur- 

 nace, and the discharge of the iron at the tap hole at 

 the bottom. 



The blast which enters at the point (', in Figures 1 PLATE 

 and 2, produces the greatest heat a little above this ' 

 point, where the iron and the cinder are melted, and 

 where the former drop* into the cavity D. The oxygen 

 of the atmosphere, in making its way through the 

 combustible matter, soon combines with it, so that 

 i>r very little, escapes from E to A. This part of 

 the furnace, which we have called the cementing part, 

 contains the ore and coke mixed together, and i 

 will be affected just as they would be in a close vessel, 

 that is, the oxygen of the ore combines with the carbon 

 of the coke, forming carbonic acid, or rather, perhaps, 

 carbonic oxide, which it generally the case at this 

 single temperature. This change will go on, in each of 

 the masses of ore, to the very centre, when it consists 

 of metallic iron and earthy matter only. As soon as 

 the oxygen is separated from the Iron, the combination 

 jdftoarDon with the metal cornmcnces-^ndilkontinues 

 till, from, the reduction of the mass belffw, it is in its 

 turn brought to the melting point, when the lime com- 

 bines with the earthy part of the ore, and the liquid 

 metal fills down. The vitreous cinder, thus separated, 

 alto becomes iron, and being specifically lighter than 

 the liquid iron, floats on its surface. 



The melted iron occupies the part D, Fig. 1. and 2. 

 in the furnace, and the cinder floats above it, till it 

 runs of over the part d, which is called the dam ttonr. 

 As the metal accumulates, the cinder is raised, and runs 

 over the dam stone ; and the metal itself ultimately 

 would run over the same ; but, previous to this, it is 

 let out at the tap hole r, Fig. 5., which is on a level Fig- 5. 

 with the bottom of the cavity which contains it. 



The quality of the metal, with respect to its quantity 

 of carbon, will depend upon the quantity and quality 



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