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<ngine.'s power uieJ formcvly lo compvefs tKe air to 3 or 

 4 lb. would now be employed ia a blownng cylinder of larg- 

 er diameter, raifiiig per minute, or indeed per ilroke, from 

 ICO to 200 cubic feet of ah'. Oppofed to this there (land 

 two formidable objedions, refulting from the neceffity of 

 iilinj^ blow-pipes or nozles ot increafcd dliimeters, fiom 

 •-vliich to difchargc the additional quantity of air, '.iiaking up 

 in area what is wanting in velocity to difchargc the air in a 

 ^iven time. The full h a re-aftion of tlic uir, fo powerful 

 as to iffue back from the tuyere with a vclocily little (hort of 

 that at which it enters. This, with uofc-p-.pes of .2, 2 1, 

 and from that to 3 inches, is fcarcely ftlt when the blall is 

 foft, and may be entirely obviated by a judicious arrange- 

 ment of the tuyere iron and nole-pipe ; but with pipes 

 from 3 to 4 and 4' inches diameter, the recoil increafes 

 as the fquares of the diameters ot the blowpipe,-, ;i!id even iu 

 denfe blafls the recoil increafes with the diamettr uf the dif- 

 charging pipe. It is therefore probable, that to blow with 

 a nolepipe 4 or 5 inches diameter, lo as to Rave no recoil, a 

 velocity or denlity of air would be requifite beyond any 

 thing yet in ufe. 



Thofc who advocate for the ufe of a foft blaft, cither 

 upon the plea of their materials, or as being the moll advan- 

 tageous method of uling any given mechanical power, fre- 

 quently feel the full cffeAs of the recoil of a confiderable 

 portion of the whole blaft. But to obviate this, and to gain 

 the advantage of the whole air, the blowpipe is enclofed in 

 a moveable frame or building, which is made air-tight at- 

 •every call, and completely prevents the return of the fmallell 

 portion of it. The combulUon at thefe furnaces is carried 

 on with equal effecl, and the refulting produfts in iron equal 

 in point of quantity and quality to thofe where blalls of double 

 denfity are uled. 



Again, at other furnaces, where a foft blad had been ori- 

 ginally preferred, the plan of forcing back the recoiled air, 

 in order to make up in quantity what was now deemed to be 

 deficient in denfity or velocity, has been in vain attempted. 

 The tuyere irons have become immediately heated, and burnt 

 back will, violence. The materials would not admit of the 

 tuyeres being raifed fufficiently high to prevent the cinder 

 from flowing back into the bag, which connects the large 

 and fmall pipes, and dellroying it. Even, in more than one 

 inllancC; the entii'e tuyere lide of a furnace has been loft in 

 endeavouri:)g to tllablilli this plan of blowing, where either 

 the materials would not anfwcr, or fron fome mifconception 

 in the mode of operating. Where a furnace works uniformly 

 with a dark or honey-combed tuyere, this mode of blowing 

 may be attended with the gre.itell fuccefs. In all new erec- 

 tions, however, the blaft ought to polTefs of itfelf fuffieient 

 velocity not only to enter the turnace, but to afcend through 

 the materials, without admitting of any important recoil. 



The fecond objeftiou, ariling as a confequence of the 

 want of velocity, and of being obliged to ufe pipes of a 

 larger diameter to carry in the full complement of air, arifcs 

 from a belief that a large pipe never makes the metal of a 

 good quality. This dtduftion is perhaps not altogether 

 correct ; but it fcems highly probable, that in the ufe of a 

 comparatively loofeblaft, only almall portion of tlieair pafTes 

 , through the furnace without decompofition. The point of 

 feparatioQ may by this means be changed, or perhaps be 

 raifed too high for the prefervation of the metal, immedi- 

 ately previous to feparation. As the increaled temperature 

 prevails upwards, the affinity between the particles of metal 

 in the iron-llone, and t!ie carbon of the fuel, may be earlier 

 ellablilhed, and no ultimate evil confequence, in point of 

 reafoning, ought to enfue. It appears from numerous ob- 

 fervations, that the quantity of iron-ilone, which a given 



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weight of cokes fmchs, and to the metal of which is conveyed 

 the carbonaceous principle, is confiderably dependent upon 

 the diameter of the blowpipe. Suppofing the ore of equal 

 richiiefs, the fmaller the pipe, the greater burden will the 

 coke carry, and the cheaper will the iron be made per ton, 

 fo far as r.uiterials are concerned. On the contrary, with 

 large pipes, whatever the denfity of the air may be, the quar.- 

 tity of coals nccelTary to manufafture an equal quality of 

 pig iron will be incieafed, and the coft of the iron is alfo 

 enhanced. As an equivalent for this, however, the quantity 

 is confidcrably increafed with nearly the fame amount of la- 

 bour ; fo that it remains a queftion with the manufafturer, 

 whether the additional coil of coal is compenfatcd by the 

 extra produce of metal he is enabled to bring to market. 



4lh. The quantity of air difeharged into the furnace, un- 

 der the appellation of blaft, depends upon the number of 

 ihokes or cylinders which the engine makes per minute, 

 and on the area and diameter of the air pump. This is in- 

 dependent of every confidcration of denfity and increafe of 

 power in the fteam cylinder, fo long as the blowing or air 

 cylinder remains the fame, and the engine performs the fame 

 difcharges ; the meafure of atmofpheric air, which enters 

 the furnace, will remain the fame. The rapid improvements, 

 which of late years have been made in the blowing machine, 

 have increafed the quantity from 1000 to 4000 feet per mi- 

 nute per furnace ; and the quantity or produce in ii-on has 

 been alio confuleiably increaled. We by no means, how- 

 ever, find that the increafed manufafture of iron has been in 

 the exaCl ratio of the quantity of blaft thrown into the fur- 

 nace. Many inftances of late years have been noticed dtir- 

 ing the tranfition from the old to the improved modes of 

 blowing, wherein the proportion has had little or no fimila- 

 rity. 



Fifteen hundred feet of atmofpheric air in one minute was 

 found in moft fituations equal to the maniifafture of twenty 

 tons of melting iron ; in the fame fituations, 3000 feet in 

 the fame time has never exceeded thirty tons per week ; and 

 in one particular trial for two weeks, the difeharge of 60CO 

 feet, being the whole produce in air of tlie engine, the pro- 

 d'lce in iron never exceeded 36! tons. In the laft cafe, the 

 quality of the iron was irregular, and the quantity of cokes 

 for each ton of metal thus produced was conliderably in- 

 creafed, although the iron was of inferior carbonation. 



Without recurrence to the diameter of the air cylinder, 

 and the particular movements of the engine, the fame fafts 

 have been frequently deduced from the diameters of the nofe- 

 pipts. We have frequently feen air ditciiarged under a pref- 

 fure of 2 J lb. upon each fquare inch, but with a pipe of zl 

 inches diameter, reduce materials, and manufacture good 

 melting iron to the extent of 20, 22, and 25 tons per week; 

 and in the fame furnace, and with the fame materials, the 

 air difeharged by 2 pipes, each 2\ inches, under a prelfiii-e 

 of 3 lb. upon each fipiare inch, the produce never exceeded 

 30 tons of metal of an equal quality, but more frequently 25 

 to 28 tons. One obfervation Itill more diredl, and made witli 

 a blaft of a denfity equal to 2| lb. per inch, and difcliarged 

 by one pipe of 2{. inches diameter, frequently manufactured 

 22 tons fine melting iron weekly ; another pipe was added 

 to the oppofite tuyere of the fame diameter, and the quantity 

 of metal weekly was never increafed beyond 32 tons, and 

 upon an average of fix months only 27 tons. Thefe are cu- 

 rious fads relative to the nature and effefts of blaft, and ex- 

 liibit the invcftigation of its principles as a matter of fingu. 

 lar importance in the economy of the manufaflure. 



One remark was made relative to the burden of ore in the 

 laft ftated faft, that with the fmall pipe a given weight of 

 cokes fmeltcd and carbonated the metal in 3 cwt. ol iron- 



ftone; 



