the temperature to which it is raised and the more sudden the cooling, the greater is the hardness. On this principle is based the process of tempering, by which any desired degree of hardness is obtained. The different temperatures are indicated by a succession of colors which the metal takes while heating, and these colors consequently serve to direct the workman who seeks to obtain the hardness that is appropriate for certain uses. Thus a very pale straw color, corresponding to 430° F., is the right color for lancets; a deeper shade, 450°, is adapted for razors and most surgical instruments; an orange yellow, 470°, for penknives; a brownish yellow, 490°, for cold-chisels; a brownish yellow tinged with purple, 510°, for plane irons; a purple, 530°, for table knives and scissors; a pale blue, 550°, for swords and watch springs; a common blue, 560°, for fine saws and dirks; very deep blue black, 600°, for pit saws. At 630° it becomes sea-green, but above this temperature the colors disappear, and if slowly cooled the steel becomes very soft, so that it can be worked with ease, after which it may be tempered as desired. A more exact method of tempering than by the color is to immerse the steel in heated baths of mercury or of oil, the temperature of which is carefully regulated according to the indications of the thermometer, graduated up to the boiling point of mercury. The cooling may be effected by plunging the articles into cold water, into cold mercury, or oil, or if they are very small by waving them through the air. By hardening steel its volume is increased.-The early history of steel is involved in much obscurity. It is supposed that the substance was known to the ancient Egyptians, and that articles made of it were designated in their drawings by a blue color. In the Hebrew language there is no word specially applicable to it; but it is supposed the hard "iron from the north," spoken of in Jeremiah xv. 12, may have been steel from Chalybia, a country famous for its iron production. There are several allusions in the old Greek authors to the hardening of a metal, commonly understood to be steel, by plunging it when hot in cold water; thus when Ulysses pierced the eye of Polyphemus with a burning stick, Homer describes the hissing as like that of red-hot iron when plunged by the smith into water to harden it. Aristotle describes the processes of the Chalybes by which they converted iron into steel, purifying it from the scoria by a succession of meltings. The word σTоμwμa, applied to the new product, is used by various Greek writers to designate something distinct from odnpos, iron, and, when described at all, having the peculiar hardness and uses of steel. Daimachus, a writer contemporary with Alexander the Great, names under the same designation four varieties of steel: the Chalybdic, suitable for carpenters' tools; the Lacedæmonian, for files, drills, gravers, and stone chisels; the Lydian, for the same and also for knives and razors; and the Synopic. The Latin

At

writers called the same substance acies, and ferri acies, whence the French acier, steel. Beckmann affirms on the authority of Hesychius that the term adamas originally meant steel, and should be so translated when applied to chains, bars, gates, &c. Yet it is remarkable that no articles of steel have been found among the relics of the nations of antiquity, even to the period of the Roman empire. The iron and steel of India are both mentioned by ancient writers, and the latter is supposed to be the same as the wootz, of which 100 talents, called ferrum candidum, were presented to Alexander in India, and which is still prepared there by a very primitive method. The Hindoos charge their crucibles with bits of malleable iron, mixed with wood and covered with the leaves of trees, which, when the metal is thoroughly heated, furnish the carbonaceous and nitrogenous elements of the steel. Fusion ensues, and the steel, of very superior quality for fine cutlery, is finally found in a button at the bottom of the crucible. During the middle ages the art of making steel existed in the highest perfection in Turkey and the countries of the East; but in western Europe it was comparatively little known. Eisenärz in Styria it has been practised ever since the 8th century. Even as late as the 17th century few persons practised it in England, and the first patent granted for this manufacture was dated April 8, 1626, to Richard Lord Dacre, Thomas Letsome, and Nicholas Page, for " apparatus for making steel," according to the invention of Letsome. Foreign iron alone was used for it. About 1670 mention is made of steeling articles by "boiling them in sow-metal." The carbon of this is given up to the wrought iron articles in sufficient quantity to convert them into steel; and by Vanaccio this was carried so far that the cast metal was also brought down to the steel point, making however poor steel. This is probably the same operation that is spoken of by Agricola, Imperati, and others, as practised at an earlier period on the continent. The manufacture by cementation is said to have been practised at Bromley by John Heydon as early as 1697, but was first made generally known by Réaumur, and described in his work on steel published in 1722 (see RÉAUMUR); and cast steel, it is stated, was first made by Mr. Huntsman at Attercliff, near Sheffield, in 1770. The subject attracted some attention in the Connecticut colony as early as 1655, when the assembly of New Haven granted privileges to John Tucker of Southold, Long island, who undertook the manufacture. There is no record however of his succeeding in it. Joseph Higby, an ingenious blacksmith of Granby, Conn., who also distinguished himself by his coinage of the Granby coppers, memorialized the legislature of Connecticut in 1727, that he had "with great pains and cost found out and obtained a curious art, by which to convert, change, or transmit common iron into good steel, sufficient for any use, and was the very

first that ever performed such an operation in America." He produced samples of good steel, and obtained a patent for 10 years.-Steel is obtained, first, either directly from iron ores, the carbon being infused into the iron as this is revived from the natural oxides; or, second, from cast iron, by removing from it a portion of the carbon it contains; or, third, from bar iron, by causing this to absorb a due proportion of carbon; and in procuring it from each kind of manufactured iron several processes are employed. From certain rich magnetic ores steel may be worked in a small way directly, even in the blacksmith's forge; and in the Catalan furnace the manufacture has been carried on upon a considerable scale. When this is the special object of the operation, the process of reduction is somewhat varied, with the view of checking the decarbonizing action before it is carried to the point of malleable iron. The operation is stopped at a point determined by experience, when the loop is removed and drawn out into bars under the hammer. By long continued hammering the steel thus obtained may be made to acquire a tolerably uniform density and composition; but a more expeditious method is to convert it into cast steel by melting in crucibles, in which condition it is kept from 3 to 4 hours, when it is poured out into cast iron moulds. The method is not largely practised, owing to the want of uniformity in the product.-Among the methods of treating cast iron for steel, that of partial refining by puddling has been long practised in Isere in S. E. France, in Thuringia, Westphalia, Styria, and Carinthia. What is known in this country as German steel, produced from pig iron made from spathose iron ores, is chiefly puddled steel carefully refined. In Isère the cast iron, usually gray, sometimes a sublamellar white iron, is first melted in a furnace with a single tuyère, together with rich scoria of the preceding operation, with charcoal. The iron is slowly brought to the melted state, and is thus kept about 8 hours. The refining then commences, and lasts about 6 hours. The temperature is kept lower than in ordinary refining fires, just sufficient for the scoria to remain in a fluid condition. The charge is worked up with a ringer, as in ordinary puddling, and the oxygen which removes the carbon from the cast iron is in part derived from the oxide of iron of the scoria. To check its too rapid action the draught is diminished and silicious sand is thrown in. Steel "comes to nature" at the surface, forming a spongy crust. This is broken up, pushed toward the extreme end of the furnace, and formed into little loops of 30 or 40 pounds weight each. As these are produced about one every 10 minutes, they are taken out and hammered into blooms. About 8 hours are required to remove the whole charge of about a ton weight, making 22 hours for the whole operation. The blooms are afterward heated in a separate fire, and then drawn down into bars. About 132 parts of cast iron are

required for 100 of steel. In Westphalia lamellar manganesian white irons, which are rapidly refined, are treated for steel in furnaces like the refinery fires. The cast iron is thrown in, in quantities of about 75 lbs. at a time, and when sufficiently refined the loops are taken out and drawn down under the hammer. The steel is used for making scythes, cutlery, and swords, after being well refined. In the New Jersey iron region, and in that of N. New York, puddled steel has been made to some extent. The best charcoal iron is required for the purpose, and manganese is sometimes added to the charge, the purpose it serves being apparently to lengthen out the time of the refining, and thus diminish the risk of passing the desired point of decarbonization. The process requires much care and skill on the part of the workman, and the product is rather a steely iron, or mixture of steel and iron, and this of varying and uncertain quality, than good steel. Whether puddled steel has ever been cast or not is uncertain. It is supposed that this may be done in Krupp's works at Essen, which will again be referred to. Other methods of treating cast iron for steel will be mentioned, after describing the process in general use of producing steel from bar iron. Nearly all the steel of commerce is prepared from bar iron by what is called the "cementation process." It consists in exposing the iron, buried in charcoal, to long continued heat. The operation is conducted in a furnace resembling externally that used in the glass manufacture, in the base of which, under an arch, are set two horizontal troughs made of fire slabs, each of them from 8 to 15 feet long, and from 26 to 36 inches wide and deep. Bar iron, made from magnetic ores with charcoal, is selected for making the best steel, and the English works are supplied with such iron from Sweden and Russia, the choicest brands being those known as hoop 1, ; GL, G; and the double bullet, ; all produced from the ores of the famous Danemora mine. These irons are worth in England from £30 to £33 per ton, and, with other irons imported from Sweden, Russia, and Norway, are used in the manufacture of steel to the extent of 35,000 tons annually. The poorer English steel irons, worth £11 per ton, are used to the extent of about 20,000 tons. The bars are cut into lengths somewhat shorter than the troughs, and a bed for them being prepared in these about an inch deep, of pulverized hard wood charcoal mixed with its weight of ashes and a little common salt, the bars are laid in this edgewise, about half an inch apart. The charcoal mixture or "cement" is then sifted over the bars and pressed between them, so that each one is in contact with nothing else. When the bars are covered about an inch deep, another tier is added, each bar over the space between two bars of the bottom layer. The same packing with cement is repeated, and other tiers are added in the same manner,

till the chests are filled within 3 inches of the top. This space is then closed in with cement from a previous operation, and covered over either with damp silicious sand or with fire slabs, the joints plastered with fire clay. A complete charge is commonly about 15 tons; some furnaces hold 18 to 20 tons. In the end of the chests some of the bars in the centre are made to project through openings left for the purpose and through the brickwork in front, the object being to draw them out in the course of the process for indicating its progress. The fire is started and gradually increased for the first 24 hours, and after this the heat is kept at about 100° of Wedgwood's pyrometer, necessarily below the fusing point of steel. In 6 days the first examination is made, and in 2 more the bars are commonly found to be converted into blistered steel, so called from the blisters all over its surface, produced it is supposed by the insinuation of carbon beneath scales of the metal imperceptibly united to the mass; it has also been suggested that in the imperfectly welded places oxide of iron is formed, the oxygen of which uniting with the infiltrated carbon produces carbonic oxide and lifts up the metallic scale. The bars gain about in weight and about in length. From the manner in which the carbon is introduced, the steel cannot be homogeneous, but contains most carbon in its outer portions. If soft steel is wanted for springs and saws, the process may be stopped several days sooner than if a higher steel is required, suitable for files, chisels, and other cutting tools. The fire is stopped and the furnace is left for about two weeks to cool before the bars can be taken out. They may then be applied to a variety of ordinary purposes, as some agricultural instruments, table cutlery, coach springs, &c.; but to produce steel of good quality other operations are necessary. What is called shear steel, so named from its having been originally employed in the manufacture of shears for dressing woollen cloth, is made from fagoted pieces of bars of blistered steel, heated to a full welding heat, in which they are protected from oxidation by a coating of very fine clay, and drawn down under the tilt hammer to a bar two inches square, or any other desired size. The tilt hammer for finishing the small bars weighs only from 150 to 200 lbs., and is so constructed as to be worked with great rapidity, striking from 200 to 300 blows a minute, thereby keeping up the heat in the bar through the intense friction produced among the particles of the metal. Heavier hammers are also used, with heads faced with steel and weighing about a ton each. By this operation the steel is much condensed, and rendered of uniform quality and homogeneous structure throughout. Its tenacity, malleability, and ductility are increased, and it becomes susceptible of a high polish. By doubling the bar and repeating the operation the character of the metal is still further improved, and it is then known as double shear steel. The manufacture up to this point is carried on upon an extensive scale

in many large establishments in Sheffield, England, and both the blistered and shear steels are sold, to be converted by other manufacturers into the various objects of their operations.-But steel is carried to a still higher degree of perfection by another operation, which converts it into what is known as cast steel. This consists in melting in crucibles the bars of blistered steel, broken in pieces of a pound weight or less. The furnaces, one for each crucible, are partly sunk below the floor of the foundery, and are intensely heated by coke, or in the United States by anthracite. The largest measure about 20 inches by 16, and are 3 feet deep. The crucible, charged the first time used with 36 lbs. of metal, the second time with 32 lbs., and the third and last time with about 30 lbs., is introduced from the top upon the grate bars in the midst of the fuel; and the cover being put on the fire is driven by the strong blast derived from the high chimney, and kept up from 3 to 4 hours. The crucible is then lifted out, and its contents are poured into the cast iron ingot moulds. The ingots are hammered or rolled into bars or sheets, and the steel thus obtained is of the hardest and densest character, requiring much care in forging that it is not hammered at a heat above a cherry red, when it is in danger of being broken to pieces. It is made into bars of various shapes and qualities, and is very largely produced in Sheffield for domestic use and exportation. Great care is taken to insure a uniform quality in each sort of steel sent to market, and also the exact quality suited to the particular use for which the steel is designed. Each ingot is not only examined to insure its uniform character, but it is also appropriated to the special use for which, according to its tenacity and hardness, it is found to be adapted. Many important tools require a particular grade of steel, and constant practice and long experience are necessary to appreciate the differences of quality. But notwithstanding all this care large lots are occasionally returned to the makers by manufacturers in this country, who find the steel ill adapted to their purposes, although from the same houses that have previously supplied them satisfactorily. It is not strange then that consumers are unwilling to incur the risk of trying a new variety, especially when so many instances are before them of failure on the part of novices to produce continuously good steel of uniform quality. Every one therefore who engages in this manufacture does so in the face of serious difficulties, not merely in producing a good article, but in getting it recognized as such, and a sale established for it. The most important improvement introduced of late years in the manufacture resulted from the experiments of Mr. Heath of Sheffield, who sought to produce with English iron steel like that made with the Swedish. The great difference in their qualities, it was thought, might be owing to manganese, which was always present in the Swedish iron. In

1839 he succeeded in producing a carburet of manganese, which caused the English iron to make good steel. He patented the process, but not the improvement he made upon it of using the carbon and manganese separately. This the Sheffield manufacturers adopted, and between 1839 and 1855 it has been estimated that the saving to the buyers of Sheffield cast steel goods by reduced prices in consequence of this invention has been equal to £2,000,000. But Mr. Heath was no more benefited than was Cort for introducing the puddling process; and he died in 1850 poor and broken-hearted.-Among the new processes of making steel, that of Bessemer (see IRON MANUFACTURE, vol. ix. p. 607) has attracted the greatest attention. It appears to be still on probation in Europe, and is spoken of as being tested in works especially built for the purpose in Sheffield. Little is stated as to the cost of the steel made by this process, or of its uniformity of character; but some of the steel produced by it possesses a wonderful tensile power. A bar 3 inches square was bent round until the outer curve was lengthened from 12 to 16 inches, and the inner lessened from 12 to 7 inches, cold and without a flaw. Four iron rods, 1 inches in diameter, were twisted cold into a cable; the rods stretched 1 foot in 4 during the process, and thinned out in inverse proportion. A steel bar 2 inches square was twisted cold into a spiral at an angle of 45°. A round steel bar was hammered cold into the form of a horse shoe. The manufacture of steel by this process is reported to be carried on in several localities in Sweden, especially by Daniel Elfstrand and co. of Edsken; and by Mr. Göranson of Gefle in Sweden large steel circular saw plates have been made from ingots cast direct from the fluid metal within 15 minutes of its leaving the blast furnace. The old firm of James Jackson and son near Bordeaux, France, is also reported to have adopted this process in preference to the manufacture of steel by puddling; and it was also about being adopted at 4 blast furnaces belonging to other establishments in the south of France. In Belgium and Sardinia it was also about being introduced.-What is known as the Uchatius process was introduced in 1856 by Captain Uchatius, engineer of the imperial arsenal at Vienna, and consists in melting in crucibles cast iron reduced to small particles and intimately mixed with some compound of iron and oxygen. Brown spar or the spathose protocarbonate of iron, with some oxide of manganese, was found to be well suited for the purpose. The quantity of oxide is graduated to furnish just the amount of oxygen required. The cast iron is granulated by causing it, as it flows from the blast furnace, to be dashed and scattered by the floats of a wheel from which it falls into cold water, and the smallest pieces are preferred, even such as weigh 1,000 to the pound. The most intimate mixture is thus effected, and the chemical change takes place most readily and thorough

ly, resulting in homogeneous steel of the softest quality. As the oxide of iron gives up its oxygen to carry off a portion of the carbon from the cast iron, it is itself reduced to the metallic state, and adds to the quantity of steel obtained, which is thus somewhat greater than of the cast iron employed. The mixture for producing 25 lbs. of steel consists of 24 lbs. of granulated iron, 4 lbs. of spathose ore, 4 lbs. of oxide of manganese, and a little clay. The conversion is completed in 2 to 3 hours, when the steel is poured into the moulds. The method is improved for irons of inferior quality by adding a portion of alkaline earths to the charge, the effect of which is to remove the impurities which readily combine with these as the granules melt.-Other methods of decarbonizing cast iron to the steel point are also practised. One consists in melting together proper proportions of bar and cast iron for the carbon contained in the latter to produce the sort of steel desired, when it is divided throughout the whole of the iron. A patent was granted for it a few years since to G. Brown, of Swinton. He mixes in a crucible small pieces of charcoal, with pieces of bar iron and of pig iron. For a 40 lb. ingot, the proportion of cast iron varies from 7 to 12 lbs., according to the sort of steel, mild or high, required. The great proportion of the charge is necessarily bar iron, and whenever this is to be melted great expense is incurred in crucibles, the best standing only 2 or 3 heats. The best sorts of iron must be employed, there being no provision for separating and removing the noxious elements usually present.-A method of converting malleable iron into steel by fusing it in the presence of an alkaline cyanide, has within a few years past been introduced into practice upon a large scale in the vicinity of New York. For a long time it has been known to workers in steel and iron that the latter might be superficially hardened by fusing upon it the cyanide of potassium; but it was not known that steel might thus be made in the large way until the fact was demonstrated by Prof. A. K. Eaton, who, while lecturing upon chemistry at Little Falls, N. Y., was led to engage in a course of experiments in this direction. He first studied the action of cyanogen, a gaseous compound of carbon and nitrogen, upon incandescent iron; and then of the solid compounds of this gas in the form of the cyanide or ferrocyanide of potassium (prussiate of potash) and cyanide of sodium. He found that iron raised to a bright red heat in a porcelain tube, or otherwise protected, was rapidly and perfectly converted into steel, by passing over it cyanogen gas; also that iron wire introduced into the flame of a burning jet of cyanogen was similarly changed by absorption of carbon. Bars of iron were then packed in fine charcoal with an admixture of yellow prussiate of potash or other cyanide, and at a high temperature these in a surprisingly short time were thoroughly converted into steel. The object of the charcoal is explained