IRON. 



tlu' air to afcend from a deep pit, by a pipe communicating prongs of a 'common fork made by this procefs can "hi 



with the blowing cylinder. This contrivance, however, welded together with the greateft facility. Pig-iron, until 



fiiould be alaid aliJe whenever the air of the atmofphcre lately, has been confidered a much more complex body thai 



becomes colder than the average temperature of the earth. experience has warranted. We have lieard of its being fup. 



With regard to the defcft aril'mg from increafe of vohime of poled to contain filex, or, according to Mr. Davy, filicum, 



tlie air in the fummer months, the heat caufed by the fric- to which it owes fome of its crude qualities. But the pro- 



tion of the blowing piilon will be found to contribute much cefs juft mentioned is fufficient to refute the afi'ertion. Iron 



to the evil. The air by this means gets an additional elaf- mailers, even at this day, however, will talk about oxyge:i. 



ticity, and if the faFne quantity of air be thrown into the ated pig-iron, meaning that wliich is loall carbonated ; but 



furnace it mud be effeiSled by dccreafmg the prefTure of the it mull be clear to every one acquaii.tcd with the chemical 



biaft, or by increasing the aperture of \.\\e nofe-pipe. If the qualities of thofe bodies, that the profcnce of carbon and 



compreiTion of the air could be effeded by any means which oxygen in a liquid mafs is perfrftly impoflibie, as they are 



would avoid the friclion of machinery, it would no doubt incapable of exilling together uncompoiinHed at any fuch 



be a defidei-atum in the procefs of blowing. It will appear elevated temperature. Hence v.-e muli regard pig-metal 



from thefe facls, that in fummer, when the quantity of air as a compound of iron and carbon only. Manganefe may 



is deficient from increafe of volume, and from the prefence periiaps fometimes be prefent in it, when particular ores 



of water, that a larger quantity of air fhould be made to are employed for fmelting, but its union mull be confidered 



enter the furnace, partly by increafing the velocity, and as accidental. 



partly by ufing a r.ofe-pip: of greater diameter. If the To make pure iron, therefore, we have, from thefe con- 

 deficiency were made up by the increafe of prelTure only, clufions, only to extricate the carbon. This may be done, 

 the velocity would be too great for producing a maximum in fmall mafles, by llratifying the articles in a clofe veficl 

 of combuftion. where it is immediately wanted, independent with fome fubftance containing oxygen. The poorer iron 

 of the mechanical evil it would be liable to produce. If, ores, which are free from fulphur, are ufed in powder for 

 on the other hand, the apcrtu.'-e of the nofe-pipe were in- this purpofe ; and after the 'materials have been expofed 

 creafed in fumm.er, to make the quantity equal to that of to a heat juft Ihort of the fufion of the metal, the air being 

 ■winter, the air would enter in a ilate of greater rarity, and completely excluded, the carbon will become difTipated, 

 the combuftion would, from this caufe, be of lefs intenfity. and the iron left in a Hate of purity. See Casting and 

 This circumllance alone, perhaps, is fufficient to prevent Fouxdery. 



a comolete remedy of the evil, and will go far to explain . _, . - „. . . ,j u r , o r 



the difference between the fraftions refulting from calcula- f +• Converjon of Ptg-tron into malleaUc Iron, and St.-cl. 

 tion and experiment. I. Bar, or wrought Iron — Iron, as obtained by the re- 



We fhall conclude our account of this ^department of duftion of its ores in the blaft-furnace, contains, as we have 



iron-manufadlure with fome general obfervations upon the before ftated, a certain proportion of carbon, which renders, 



nature and properties of pig-iron, as it is applied to different the metal unfit for the various purpofes of forging, but 



purpofes. conllitutes its principal value as applicable to the ufe of 



When the iron has combined with its full dofe of carbon, the founder. To deprive it of this ingredient certain pro- 

 conilituting what is called in the trade, grey, or fmooth- celTes are gone through, the ob'iecl of which is, by the con- 

 faced iron, and alfo N' i, it is admirably fitted for making current action of heat and air, to difiipatc the carbon under 

 the lighter and finer fort of callings, fuch as grates and the form of an elaftic compound. The kind of iron chofen 

 other ornamental work. It is from iron of this quality that for the converfion is that denominated by manufafturtra 

 the caft-iron cutler)- is manufaftured, fince no other would forge-pig. It is the loweft quality made for the purpofes of 

 run fufficiently fluid for articles fo fmall as the prongs of art; and, in confequence of its being combined with a fmaller- 

 forks, and the bows or rings of fciffors. This iron, how- dofe of carbon than any other, which thus caufes it to bear 

 ever, is not the bcl for larger caftings where ftrength and a lefs price in the market, is doubly preferable for the end 

 Imrdnefs are defirable ; as in large wheels, for example, required. 



beams, pillar?, railways, &c. The metal employed for The price of pig-iron is almoft excluGvely determined by 



thefe purpofes contains a lefFer proportion of carbon than the quantity of carbon which is in combination with it. 



the former, and is generally called melting-iron, or N 2. The varieties ufually diftinguidied are N i, ofherwife 



That fpecies of pig-iron, however, which is combined with called gi'ey, fmoothfaceil, or /i/Zy, metal; N" 2 and 3, 



the fmalleft dofe of any, is a'moll exclnfively employed for znA forgt'pig. The proportion of carbonaceous matter pre- 



making malleable iron, and is called, for that reafon,yc/r^(r- fent in thefe varieties is differently ilated by different eX". 



pig. We have given, in the next feclion, an account of the perimentahfts. Clouet makes the highefl proportion to 



proportion of carbon prefent in the different varieties ; and amount to ith ; but from the refults obtained by Mr. Mufiiet 



it will appear from thence, that of all the combinations of in combining iron direS/y with the dofcs of charcoal requiutc 



iron and carbon, ftecl contains the leaft, and grey, or N I, fo produce its various fub-caiburets, ^-'^th appeiued to be the 



pig-iron, the moft of any of the compounds we are yet maximum. Of this, the following table, pub iihed by him 



acquainted with. in the 13th vol. of the Philofophical Magraine, will afford 



As a proof that pig-iron only requires to lofe its carbon the necelfary proof, 

 to become malleable, we have at prefent in this country Soft call-fleel - - - - - - s\-e 



manufaftures upon a large fcale, for converting call metal Com.mon ditto ....-- -^{^ 



goods, fuch as nails, cutlery, &c. into iron perfeClly mal- Same, but harder .... - ^'5 



jeable, without even changing the figure given to them by Ditto, too hard for drawing . . - '.- 



cafting. Nails produced in this way arc fo malleable, even White caft-iron (fame as before callcd_/o»^i'/r^) ..' 

 when cold, as to bear the hammer, and are capable of being Mottled caft-iron (N^ 2) . . - - i^ 

 bent to a right angle in a r;ff. Black caft-iron (N' i.) - - - • .^ 



But a ftill ftronger proof that this metal alTumcd the The firft ftep in the procefs of decarbonization, according to 



form of iron u from the great keat it will bear. The the more common mode of operating, is to expofe the iron in a 



3 K 2 furnace^ 



