R O N. 



vsriety, fix of ccke to fevcn of ore. The limeRone iin- 

 bi.irnt, undw the fame circunnihnces, is to coke as four to 

 eleven ; and, for melting metal, retains a lirr.ilar ratio. Witli 

 t'le above charge per day, that is, for 12 hours, this fur- 

 nace maiies On the average about 40 tons of melting iron 

 per week. 



Some furnaces cany fo little burthen as not to yield 

 niore than 14 or 14 tons weekly; wl::!ll other;;, particularly 

 in Scath Wale?, produce, with the fame ftzcd furnace, as 

 much as 60 and even 70 tons in an equal time. The burthen 

 of thefe furnices is very great, the ore to the coke being in 

 fome cafes as i j to 7 ; and the quality of the iron is 

 ur;iforraly inferior. Sinoe the cavity in the furnace is con-, 

 ftantly kept full of the above materials, it may eafily be 

 conceived that the whole muft be in many intermediate 

 ftages, from the fully melted iron to the unchanged ore. 

 At the point where the greatell heat is produced, which 

 v.iU be a little above l!ie level of the blaft, every thing 

 capable of fufion will be affuming the liquid form. We 

 cannot, however, for a moment fuppofe, that the iron at 

 this point is in a (late of oxyd, fince it would of ntjceflity 

 Leall vitrified, and enter into tlie com.pofition of the cinder. 

 If the iron, even in its carburetted form, were to remain 

 long at fo great a temperature, and within the influence of 

 fo much oxygen, it would firft lofe all its carbon, and ulti- 

 mately pafs into the (late of vitreous oxvd. As, however, 

 the oxygen of the blaft rifes in the furnace, it comes in 

 contaft with the carbon of the coke, and is very foon con- 

 verted into carbonic acid gas. That point in the furnace, 

 therefore, where the whole of the oxygen has entered into 

 combination with carbon, may be denominated the com- 

 mencement of cementation, or the point where the oxyd 

 of iron is liril deprived of oxygen, and ultimately faturated 

 or cemenleil, as it is termed, with carbon. From this point 

 to the top of the furnace the procefs of cementation is 

 going on with different degrees of rapidity, proportionate 

 to the temperature. It is found by experiment, that if a 

 piece of iron-ore, particularly any of tlie oxyds that con- 

 tain but little earthy matter, be expofed in a clt:fe veiFel 

 in contaft with carbon, it will firll lofe tlie whole of its 

 oxygen, and afterwards become fo faturated with carbon, 

 as to be capable of fufing into the bell pig-iron. Hence 

 it appears that the reduciion of the ore, fo far as relates to 

 the deoxydation and carbonization of the iron, may take 

 place at a temperature below fufion, and without the mafs 

 of ore changing its form. The ore expofed to the car- 

 bonaceous matter in the cementing part of the furnaa?, 

 muft' as completely undergo a fimilar change as if it were 

 in the clofeft vefiel ; for the oxygen is excluded by the 

 prefence of carbonic acid gas. When the carboni-,icd, 

 but yet folid, iron, in the form of the ore, falls below the 

 cementing poinf, or perhaps Ihort of that, it begins te fufe. 

 The earthy matter of the ore, being in contaft. with lime, 

 begins alio to affume the liquid form ; and wliihl the melted 

 metal is expofed to the oxygen of the blall, a fmall por- 

 tion of oxyd of iron is produced, which will enter into 

 the compofition of the cinder, and thus tend to increafe its 

 fufibility. The liquid iron now crops into the chamber 

 of the fumace called the hearth ; and the liquid cinder, 

 behig of lefs fpccific gravity, floats upon its furface, com- 

 pletely defendirg it from the oxygen of the blaft. Hence 

 we fee that the column of the blaft-furnace may be divided 

 into three portions ; the upper portion, or cementing part ; 

 the middle, or melting part ; and the chamber, or liearth, 

 *'hcre the metal is preferved till it is in fufficient quantity 

 to be run out into pigs. The cementing portion is by far 

 Vol. XIX. ^ 



the mod extenfive, and will vary in ns extent ui-h the 

 ftrength of the bl.il^. 



Sime the combuftion muft be in proportion to the quan- 

 tity of oxygen confunied in a given time, the heat of the 

 furnace will depend upon the quantity and velocity of the 

 air blown into it to a certain extent. If the blall ftiould 

 have too great a velocity, the oxygen would pafs through 

 a greater fpace in the furnace than is dcftrable before it 

 v>'a5 diCpofed of, and the cenientiug portion would be leflcned 

 in confcquence. On the contrary, if the velocity were too 

 liitle, the heat would be confined to the vicinity of the 

 tuyere, and the cementing, as well as the melting proceflcs, 

 would be retarded for want of heat. 



When the blaft is fufficient to generate the nccefTary heat 

 for melting the cinder and the metal perfeftly, the extent 

 of the cementing portion will depend upon the height of 

 the furnace. 1 his gives us one very fatisfaclory reafon, 

 why a fm'nace is required to be higher for the ufe of coke, 

 than when it is heated with charcoal ; fince the carbon of 

 the latter enters into the compofition of the iron with much 

 more facility than that of the former. 



According to experiment, it appears that the facility with 

 which carbon enters into combination with iron, in a clofi 

 veftel, is invcrfely as it?, aggregation or cohefion. Hence 

 it is found, that the carbon obtained from animal fubftances, 

 which is foft and porous, is bett calculated to convert iron 

 into a carburet. 



It will appear from tlie laft obfervation, and from what 

 has been faid on the nature of coke, that the carbon em- 

 ployed for cementation fliould be mechanically difTerent 

 from that required to generate the great and permanent 

 heat neceiTary to the fufion of the materialsi The one 

 in the cementing portion fhould, therefore, if it were prac- 

 ticable, be furrounded with coke of the fofteft kind, while 

 the materials within the iitfiuence of the blaft, and occupying 

 the meltiug portion, fliould be fupplied with fuch as is 

 harder. 



In making the moft highly carbonized iron, or what ii 

 called N^ i, it fometimes happens that a portion of the 

 iron unites with a great excefs of carbon, forming a fub- 

 ilance, which, when cold, appears in bright fliining fcales. 

 It is found to poflefs moft ot the properties of plumbago, 

 differing from that fubltance only in containing lefs car- 

 bon. This carburet is no doubt in the liquid form in the 

 furnace, and, being of much lefs fpccific gravity than the 

 iron, floats upon its furface. It is fo much more infufible 

 than the metal, that before the iron enters the moulds of the 

 pig-bed it is feen fwimming at the top in the fcaly form 

 before mentioned. 



This fubftance is called by the v.orkm.en L'l/h ; and when- 

 ever it appears, is a certain fign that the furnace is working 

 on the beft fort of iron. So furely, indeed, is it the cafe, 

 that N I, or the moll highly carburetted metal, has le- 

 ceis'ed the epithet of ii/hy, becaufe i-iju is the common 

 attendant on its produclion. 



The moil remarkable and anomalous circumftance pre- 

 fented in the fmclting of iror, is the difference in quantity 

 and quality of the iron made in winter and in fummer, whea 

 all other things arc equal. It is a fatl well afcertainfd, that 

 in order to n;ake the fame quantity and quahty of iron in 

 fummer as in winter, tlv; furnace will not carry fo great a 

 burthen, and, at the fame time, the means of generating heal 

 requires to be increafed. 



Various opinions have been given to explain this curiou» 



faft. Some have fuppofed that the proportion of the oxygen 



was lefs in the atmofpliere in fummer than in winter. Otliers, 



3 K th.t 



