IRON. 



Jsept in more I'nan twelve hours in tlie day, and this will not 

 allow of more than three heats. For the beft poflible caft- 

 ftcel, the bars of the beft bliftered-fteel are broken into fmall 

 pieces, it beint;, on coining from the cementing furnace, fiif- 

 ficiently brittle fur this purrofe. An inferior kind of ca'\- 

 fteel is made from the fcraps, which confill of tlio wafte of 

 the manufaftories. The heat required to melt ftecl is very 

 great ; and inverfely as the quantity of carbon combined 

 with it. Before caft-fteel making was brought to great 

 perfeftion, the quantity of carbon given to it was greater, 

 in order to effeft its more eafy fufion. The crucibles and 

 furn-.cef, however, are now fo much improved, that the 

 fteel can be melted with much lefs carbon, and it is, in con- 

 fequence, fo l':rul, to ufe a technical piirafe, as to weld with 

 iron, and even to be capable of u'.ii:ing two pieces of it to- 

 gether. 



After the ftsel has become fufficiently fluid, it is poured 

 into call-iron moulds, which form it into ingots of an ofta- 

 gonal iliajje ; and are about 30 inches long, each weighing 

 about 3olbs. Formerly, the great fecret of making cart- 

 Heel 'ras faid to confill; in ulin^ fome peculiar flux. No fub- 

 ftance, however, from what has been obferved, can increafe 

 the fufibility of the fteel, hut an additional dofe of carbon, 

 which is improper after a certain quantity has been united 

 with it. Th ■ only fubftance, 'herefore, which can be em- 

 ployed to any advantage, muft be fome fufiMe vitreous 

 matter, capable of floating upon the furface of the metal, 

 and defending it from tlie contaft of air. 



The flux at prefent ufcd, and the moll proper for this pur- 

 pofe, is the blaft-furnace cinder. But pounded glafs, or 

 any vitreous fubilance which fufes a little before the metal 

 melts, will anfwer equally well. 



The ingots of call-fteel, as well as the bars of bliftered- 

 fteel, and (hear-fteel, are drawn into rods ready for forging 

 into various articles, by a piece of machinery ca'Ied a tilt, or 

 tUting-miU. (See Tiltixg-mill.) By this hammer, the 

 caft-fteel can be drawn down to the iize of ^ inch fquare. But 

 in reducing fmaller than that, it would be liable to be injured 

 in its fabric. It is drawn into rods of fmal'er fize by hand, 

 for the purpole of making gravers, and watch-makers' 

 tools : and for ftill more delicate articles, it is manufac- 

 tured into wire. Tiie bliftered-fteel will not bear drawing to 

 a fmall fize, on account of the loofenefs of its texture. 



Steel is of a mean fpecific gravity between wrought and 

 pig-iron ; and, like the former, it increafes its property in 

 this refpeft by hammering. Like iron, too, it becomes 

 fofter on being annealed, but never becomes fo foft as that 

 metal. When of good quality, and at a certain degree of 

 hardnefs, it is ftronger than iron ; that is, when ftretched 

 longitudinally by a weight ; but, by fudden bending or twift- 

 ing, it is more liable to break ftiort. In working it with the 

 hammer, it will not bear fo great a heat as iron ; fince the 

 temperature iron and its combinations fuftain without melt 

 ing, is inverfely as their dofe of carbon. 



This property of bearing heat, is, however, in a ftill lefs 

 ratio in caft-fteel. This is owing to its having entirely loft 

 its fibrous form in the melting. Hence there is lefs danger 

 in heating it after it has been hammered. 



In welding fteel to iron, or fteel to fteel, the fire ought to 

 be very frre from fulphur, or other extraneous matter ; and 

 the heated parts of the rods fliould be frequently fupplicd 

 witheithcr fand, or fand mixed with the fcalcs which comcfrom 

 the hammered iron. This fufes upon the furface and keeps 

 off the air. See Forge. 



The moft fingular property which belongs to fteel, is that 

 of its hardening by being heated red-hot, and cooling ra- 

 pidly. Tliis change is greater tlic hotter the fteel, and the 



colder the fluid into which it is plunged. (See Cutlekv.) 

 Water, in general, is employed for this purpofe ; and fpring- 

 water is better than any other. If the water abound with 

 animal or vegetable niat'er, the hot fteel cools more (lowly. 

 Tiii« is occafioned by a film of the matter in folution form- 

 ing and remaining upon the lurface, and, being a bad cou- 

 diidor of heat, prevents the ftecl from cooling. File- 

 makers fay, that the fait which is inevitable in their harden- 

 ing water, makes the fteel harder, and they fometimes put 

 fulphuric acid into it for the fame purpofe. 



In hardening ftecl in thin plates, fuch as faws, parti- 

 cularly when of caft-fteel, quenching in water would caufe 

 them to crack, and make them fo hard as not to be ufeful. 

 They have, in confcquence, recourfe to fome fubftance which 

 is not fo good a conduilor of heat. Oil, with tallow, bees' 

 wax. and rcfin difTolved in it, is generally employed for thefe 

 articles. ( See the article S.vw. ) If the fteel be heated red- 

 hot, it moilly returns lo its original ftate. This, however, 

 is fometimes not the cafe with thin plates of caft-fteel. In 

 giving various degrees of heat from the hard ftate, it be- 

 comes more foft and lefs claftic. See Cutlery. 



This curious and valuable property which it pofleftes might, 

 at firft view, appear to be caufed by an increafe of denfily ; 

 but the fpecific gravity of hardened fteel is lefs than before 

 it is hardened. It h.as been faid to depend upon a certain 

 cryftalline arrangement of its particles ; but this is a mere apo- 

 logy for ignorance. The moft plaufible theory we have heard 

 of IS mentioned in one of Dr. Darwin's notes to his " Botanic 

 Garden,'' and was the idea of a very ingenious friend of that 

 celebrated author. This theory was equally appHed to the 

 fingular property poflefled by the glafs toys known by the 

 name of Ptina Rupert's Drops. It is as follows. Whtn 

 the heated ileel or glafs is plunged into water, the exterior 

 ftratum becomes fo hard and folid, as not to be capable of 

 ftirinking ; and every fucceeding layer is to a certain degree 

 placed in the fame fituation. When caloric leaves a body 

 flowly, it contraAs in its dimenfions, until itafTum.es fome- 

 thing near its original volume. But if any force prevent 

 the parts from approximating, the molecules will attradi each 

 other with a power equal to the repellent energy of the calo- 

 ric that caufed the expanfion. So foon, however, as the 

 outer ftratum is broken, the whole of the others aje dellroy- 

 ed in fucceftion. This is moil glaringly the cafe with the 

 glafs drops before fpoken of, and, to a certain extent, with 

 unannealed glafs, and hardened fteel. 



With refpeclto the latter, hov.'ever, it is confined to large 

 maflTes, and particularly of caft-fteel. The rollers employ- 

 ed by jewellers and others are of call-fteel, and are very 

 liable to break in the hardening, although about half the 

 mafs in the middle is pure iron. They do not always crack 

 at the time, but at different periods afterwards, and fre- 

 quently, when no violence is apphed to them, fome have 

 been known to fly fix months after being finiflied. Some- 

 times they break with great report, and what ilrenglhens the 

 above opinion as to the caufe is, that the figure of the roller 

 is frequently changed from a round to an elhptical ftiape, . 

 For farther particulars, fee Steel. 



^ 5. Chemical Properties. 

 AVhen a piece of pohflicd iron is expofcd to the air/ 

 it foon lofes its luftre ; a.d if the atmofphere be humid, 

 it becomes covered with red fpots called rujl. Wiien 

 it is cxpofed at 400 degrees of Fahrenheit, it changes 

 to a yellow colour. The temperature being incrcafed, 

 the coL)ur gradually turns to a brown, and at the heat 

 of about 600 it becomes of a beautiful blue tint. This 

 change of colour arifes from the combination of oxygen ; 



the 



