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they cohere but fljghtly one with another. 'The knife, or the file, cannot eafily cut any one of thefe granules, but a blow of a hammer eafily feparates large 'parcels of them from thofe to which they were joined : this calf, iron is therefore, ufed only for fuch purpofes as requires a fubflance pofleiTed of thefe qualities; purpofes where hardnefs is required, and where no blows are to be met with. 'Thus backs of grates, iron pots, and the like, are made of it. One of the genera] properties of metals is, that they are malleable ; that is, their feveral particles cohere fo well to- gether, that they are ductile and extcnfible under the ham- mer, and will fuffer the whole mafs to bend any way with- out breaking, that is, without their feparating from one an- other. In the words of the artizans, fuch fupplcnefs and pliability is called body in a metal, and the caft iron, which wants this, is faid to have no body, and is what they cal' Ho fift metal. It is therefore no way fit for fuch works a: require fafhioning by the hammer or the file, nor of fuch as are to ftand any violent blows ; but as it is eafily fufible, it ferves for caft works where there is no great delicacy in the figuring, fince it does not run fo thin as to adapt itfelf to every lineament of a fine figure, nor is qualified to be repair- ed by inftruments.
The ill qualities of caft iron are, in a great degree, reme- died in the forged or wrought iron, taken from the fame quantity, and the fame fofibi*. The forging of iron is only the placing it over the fire till heated to a certain degree, and then beating it out with large hammers till it becomes foft. When it has been fufficiently forged, it becomes foft and malleable, even when cold, and when heated, is eafily wrought into any figures, which it retains always after- wards ; and it is eafily cut by the file when cold, and is not brittle on being {truck, as is the caft iron. While it gains thefe properties by the forging, it lofes, how- ever, another by the fame means, which is its fulibiiity. It will no longer melt in the fire, but when the workmen give it the ftrongeft heat they can, it is only reduced to a fort of foft pafte, and fzveats a little, as they exprefs it ; that is, fome few drops of truly melted iron fall from it. It is very certain, that both the caft and the forged iron are mixtures of metalline, faline, and fulphureous particles ; and the different arrangement of thefe, "in their mere fimple run- ning together in the fufion, and their being driven intimately into, and among one another, by the hammering, makes the fufibility different in the two ftates. If the forged iron differ greatly from the caft, there is how- ever a third ffote into which it is reducible by art, which is yet different from both, this is what we caliyW; and the quality of .iron on receiving this change is not one of its leaft. valuable ones, fince from this we have all our inftru- ments for cutting, fawing, boring, and the like purpofes, the value of which to us is almoft infinite. The German fteel has always been in great repute, and though feveral other nations have made it, yet the Germans have kept their method a facred myftery, to keep up their trade in it.
Steel is confiderably harder than forged iron, and fo it is ne- ceffary that it fhould be, in order to many of the purpofes it is employed in. Shears of fteel, which are intended to cut iron, muft be harder than iron, otherwife their edge will turn, and they will not cut ; whereas, if the metal is too hard, then the granules will fly off, and the edge break away in fmall fragments. This is the cafe with all ed^ed tools ; and hence it is that good fteel is fo nice and difficult a thing to make, fince there is required fuch a degree of hardnefs, and no more.
It is very well known, that fteel acquires its hardnefs from the plunging it into water; it is to be heated to a certain degree, and then immediately plunged, while the fiery par- ticles yet remain in it, into water perfectly cold ; it is then to be fpeedily drawn out of the water, and thus the whole operation is finifhed. It acquires its hardnefs in degrees, pro- portionate to its heat when plunged into the water; and this hardnefs, or temper, remains with it only till it is heated as high again ; for after that, if it is left to cool leifurely, and not thrown into water, it is loft. All the maffes of fteel which are fold are thus tempered ; neverthelefs, when they are wrought into tools, their temper is loft, and is to be re- newed by plunging them again into cold water, when they have been forged into the fhape of which they are to be. Mr. Reaumur affirms, that fteel differs in nothing from forged iron, except that it contains more fulphurs, and more falts. _ Hence it follows, that caft iron fhould be fteel, fince it evidently differs from forged iron in the fame man- ner, and by the ^ fame properties; and in effect, caft iron is fteel, fuch as it is, efpecially the white fort, which is more pure, and more perfectly diveftcd of its earth, than the browner forts ; and this white kind may be accordino-ly brought to all the hardnefs of fteel, by repeated heating and quenching in cold water. It follows alfo, that in order to convert iron into fteel, we are to give it new falts, and new fulphurs. It may be afked, where is the neceffify-; of giving again that, which the mere caft iron pofleffes? To which the anfwer is s that fteel is required to be malleable in fome
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degree, which the mere caft iron is not- and it is to be add- ed to this, that it may be poffiblc for us to give to forced iron iuch falts and fulphurs as are more proper for the fteili than thofe which the caft iron naturally pofleffes. We have great variety of falts and fulphurs, out of which to chufe for this purpofe, and Mr. Reaumur made many trials to find which would fucceed beft ; and the refult of all was, that for fulphurs, powdered charcoal and common foot} and for falts, fea-falt alone fucceeded beft, and that thefe were properly to be mixed with aihes, by way of an inter- mediate fubftance. Thefe fubftances muft alfo, have their allotted dofe ; that is, there muft not only be a certain pro- portion of the feveral ingredients one to another, which how- ever need not be very piecife or exact, but there muft alfo be a proportional quantity of the whole employed to the quantity of iron that is to be wrought upon ; and in this alfo regard muft be had to the feveral forts of ores from which the iron was obtained, fince the iron of fome ores is much fooner convertible into fteel than that of others, and makes alfo a better fteel.
The manner of beft introducing thefe falts and fulphurs into the body of the iron, was found by this author a matter of great difficulty to determine. He foon perceived, that fire was the only agent that could convey thefe bodies into the metal ; and in contriving how this might be done moft ea- fily, and with leaft expence, he found out, after many trials, a new fort of furnace, which effected this purpofe with great eafe, and which was not fubjedt to the inconveniences of other furnaces.
As fteel is iron with ah admixture of heterogene particles, it follows that it muft be left metallic, that is, lefs malleable* or more brittle ; and it is alfo neceflary that it muft be, in fome degree, malleable for the purpofes it is required for; and it is eafy to conceive that thefe properties cannot be given it, in a proper degree, but by means of a very accurate operation ; and even when all the parts of the procefs are the fame, there is yet much depending on the iron itfelf, which can never be perfectly known but by trial. Something, how- ever, may be judged of the iron by breaking bars of it : the feveral forts of iron, when broken, fhew fome of them only granules, others flakes, and others fibres ; fome alfo fhew all three of thefe molecular at once, and others two of them*- but it is eafy, in either of thefe cafes, to fee which fort is in the greateft number. The laminated and the fibrous iron are the two extremes ; the firft is very brittle, the latter very malleable. The laminated iron is ever the worft of all kinds for making into fteel ; and of this kind fuch pieces are worft of all, the lamina; of which are very white and fhin- ing, and are large and irregularly difpofed, and arranged in different inclinations. Mr. Reaumur began to reckon front thefe an arrangement of all the kinds of iron, which com- ing, each by degrees, to have the laminx ftill fmaller and fmaller, and at the fame time lefs glittering, and placed more evenly together, funk at laft into the irons of the- granulated kind. It is eafy to conceive how many differences there muft be between thefe ; and from thefe the fibrofe ones may be deduced, owing their texture merely to the granulse, which in thefe are difpoied into long firings or ftreaks. Tho' in this arrangement of the irons, the firft are, of all others, the leaft proper for making fteel, it does not follow that the laft are the moft fo : thefe indeed ufually make a very foft and pliant fort of fteel, which has what the workmen call the greatejl body of all the kinds of fteel, and is therefore moft: proper of all for certain purpofes, as the making watch- fprings, and the like ; but the want of hardnefs makes it very unfit for cutting tools of all kinds, from the razor to the ax. The granulated iron always makes the tmeft and hardefl fteel; and of thefe fuch fucceed beft, whofe granules are fmalleft.
One thing remarkable Is* that all fteel, though made of iron of the granulated or flriated kind, yet is, before it has been hammered, of a flaky, or a fort of laminated ftructure ; but this feems owing to the fire's having melted fome of the granules in the operation, and run feveral numbers of them together into thefe plates. The fmallnefs of thefe flakes in fteel, which has not been worked, are a proof of its being but of a bad kind,
A bar of iron, when converted into fteel, is not equally fo converted in all its parts ; the fire has always acted more ftrongly upon its furface than on its central parts, and it is therefore more perfect fteel there than in its inner parts ; but a perfection in the operation is not neceflary to thefteel's being good and ufeful, and the whole bar is often very good fteel, as are alfo many bars made at the fame time, yet all perhaps fomewhat differently affected.
If the compofition, which is to convert the iron into fteel, be too ftrong, or if the fire be too violent, or the matter con- tinued too long in it, in all thefe cafes the fteel will be over made; that is, there will be an- over proportion of faline and fulphureous parts added to the iron : thefe will therefore too far feparate the particles of the metal afunder, and the confequence will be, that the fteel will be too brittle to bear hammering, and will be of great lofs to the proprietor in the great quantities that will be broken, betide the lofs he
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