Wade, who details them in an exceedingly clear and interesting manner. One new fact developed by them is, that iron fused a number of times up to a certain point, is thereby greatly improved in strength. In trials with some iron it was found that its transverse strength was nearly doubled by being melted and cast four times. This is a discovery of great importance to all engineers and cast-iron founders. At the South Boston foundry, experiments were made to test the strength of cast-iron which had been submitted to fusion during different periods of time. Eleven thousand pounds of iron were cast into four six-pounder guns: one after the metal had been under fusion or melted half an hour; the second, under fusion an hour and a half; the third, under fusion three hours; and the fourth, under fusion three hours and three quarters. The gun first cast burst at the thirty-first fire; the second, at the thirty-fourth; the third was fired thirty-eight times, and remained unbroken. Thus the strength of the metal seemed to increase in a ratio corresponding to the period of fusion, or under which it was kept in a highly molten state, and it might have been inferred from this that the fourth gun would have been the strongest of all. Instead of this being so, however, it proved to be the weakest, for it burst at the twenty-fifth discharge. In view of these experiments, Major Wade, in this report, says: "these results appear to establish satisfactorily the fact, that a prolonged exposure of liquid iron to an intense heat, does augment its cohesive power, and this power increases as the time of the exposure up to some (not well ascertained) limit, beyond which the strength of the iron is diminished." This is a new developed fact in relation to castiron, subject to concussions, of deep import to all engineers. Experiments were also made to test the transverse strength of cast iron bars, two inches square and twenty-four inches long, the metal of which was kept under fusion during different periods of time. These bars were set on supports twenty inches apart, and the breaking force was applied at the middle. The results obtained from four castings were in favor of that which was kept fused longest -three hours. On this head the report says, "from this it appears that the cohesive power of the iron, so far as it can be shown by its capacity to resist transverse strains, is increased 60 per cent. by its continued exposure in fusion." This is also a fact of importance to engineers and architects, regarding girders and beams, subject to a crushing force.

In most of the books which treat of the strength of cast-iron, the resistance which it opposes to certain strains is given; but little useful information can be obtained in them regarding the very great difference of strength in different kinds of cast iron. But as the density between the lower and higher grades of this metal differs as 6.9 to 7.4-a difference of 31 pounds per cubic foot, and as the tenacity of the metal has a relationship to its density, it was found by these experiments that cast iron, having a density of 6,900, had only a tenacity of 9,000; while that having a density of 7,400, had a tenacity of 45,970.

Castings of the greatest weight, according to their size, are by far the strongest, and weighing them is a ready means of judging comparatively of their strength.

Some important facts were also developed in relation to the cooling of heavy castings. At the Fort Pitt Iron Works, two eight-inch and two teninch guns were cast, one of each in the common way, solid, and one of each with a core on a tube of iron, through which water was made to circulate after casting, to cool it from the interior, according to an invention of Lieut. Rodman. The solid eight-inch gun burst at the seventy-third discharge; the hollow cast one stood 1,500 discharges, and did not burst; the solid ten-inch cast gun stood only twenty fires, while the hollow ten-inch gun stood 249. These guns were cast of the same material and at the same time, the difference in favor of the hollow cast guns is astonishing. This is attributed to the method of cooling, it being supposed that in cooling, the solid guns contract entirely from the outside, and that a strain is exerted upon the arrangement of the particles of the metal, in the same direction as the strain of the discharges.

Lieut. Rodman goes into a very subtle mathematical demonstration to show that this is the case, and that his method of cooling the casting obviates this unequal strain. But on the back of this, Major Wade presents a new fact in relation to the effect of time after the castings are made, and before they are used, which is also of vast importance to engineers. Eight-inch guns proved thirty days after being cast solid, stood but 72 charges; a gun of the same bore, proved thirty-four days after being cast, stood 84 charges, while one which was proved one hundred days after being cast, stood 731 charges, and another, proved after being cast six years, stood 2,582 charges. What in important fact is thus newly developed, showing us that solid cast iron shoul not be actively used until they have been kept for some years. Major Wade accounts for this phenomenon in cast-iron, by supposing that the particles strained in the cooling re-adjust themselves in the course of time to their new position, and become free or nearly so, and he presents some good arguments in favor of this theory.

The lesson to be derived from this by our engineers is, that heavy castings of iron for beams and machinery, subject to strains, are less capable of resisting them immediately after being cast; in other words, old castings are much stronger than new iron castings.

THE MANUFACTURE OF STEEL.

The method by which steel is manufactured is in its leading principle generally known. The interest in this pursuit must greatly increase in this country, and a statement somewhat in detail of the process of its manufacture may be instructive to many of our readers. Preparations are making to use the Lake Superior iron extensively for this purpose.

It has been clearly demonstrated that the Lake Superior iron can be converted into steel of the finest and best quality; and the Sharon Iron Co. of Pennsylvania, which owns the Sharon Iron Mountain of Lake Superior, is making preparations for entering extensively into its manufacture, intending to convert all their iron from Lake Superior into steel. The success of this enterprise (and there is no reason to doubt it) will form a new era in American manufactures, and give increased value and importance to Lake Superior iron, as no other kind in this country has been found capable of making steel that would at all compare with Swedes, English, Russia and Madras. Indeed, in Great Britain there is only one kind of iron, the Wolverstone charcoal, that can be converted into good steel; and with that exception, nearly all steel manufactured in England is made from Madras, Swedes and Russia iron.

Steel is iron passed through a process called cementation, the object of which is to impregnate it with carbon. Carbon exists more abundantly in charcoal than in any other fusible substance, and the smoke that goes up from a charcoal forge is carbon in a fluid state. Now, if you can manage to confine that smoke, and put a piece of iron into it for several days, and heat the iron at the same time, it will become steel. Heating the iron opens its pores, so that the smoke or carbon, enters into it.

The furnace for this purpose is a conical building of brick, in the middle of which are two troughs of brick or stone, which hold about four tons of bar iron. At the bottom is a large grate for the fire. A layer of charcoal dust is put upon the bottom of the troughs, then a layer of bar iron, and so on alternately, until the troughs are full. They are then covered over with clay to keep out the air, which, if admitted, would prevent the cementation. Fire is then communicated to the wood and coal with which the furnace is filled, and continued until the conversion of the iron into steel is completed, which generally happens in about eight or ten days. This is known by the blisters on the bars, which the workmen occasionally draw out, in order to determine when the conversion is completed. The fire is then left to go out, and the

bars remain in the furnace about eight days to cool. This is called "blistered steel." German steel is made of this blistered steel, by breaking the bars into short pieces, and welding them together, drawing thein down to a proper size for use.

Blistered steel when reduced into smaller bars, and beaten under heavy hammers, forms what is termed "tilted steel." The building in which the operation is performed is called "a tilt" on account of the workman, when holding a bar of steel sitting in a kind of cradle suspended from the roof, and swinging to and fro as he thrusts or "tilts" the bar under the hammer. The word "tilt," as applied to this action, and to the rise and fall of the hammer, is of Saxon origin-implying to thrust at, and also to vacillate, or to move up and down.

Tilted steel, when broken, heated, welded, and again forged into bars, is known as "shear steel," from the circumstance of its universal employment in the manufacture of the best shears for sheep-shearing.

English cast steel is another variety of this protean compound of iron and carbon, and is obtained by melting steel with vitrifiable matter and charcoal, then casting it into the form of ingots, which are subsequently gently heated, and carefully hammered or rolled into the form of smaller bars.

Blistered steel and cast steel contains 98 to 99 per cent. of iron; the remaining portion consists of carbon.

Tempering Steel.-Steel which has been rendered excessively hard and brittle by heating to redness and suddenly quenching in water, admits of having its hardness reduced, and of acquiring elasticity by a process called "tempering." This admits of the following illustrations:

Let three strips of elastic steel, of equal length and breadth, and thickness, be placed on a clear glowing fire; when they become equally red-hot, remove two of them with a pair of tongs, and drop them into cold water; then remove the third and place it upon the hearth to cool.

Take one of the suddenly quenched strips and attempt to bend it by the strength of the hands; it will not bend but break short, and will scratch glass; so that the steel by this treatment becomes exceedingly brittle and hard.

Take the strip that has slowly cooled down upon the hearth; it will bend with the same facility as a similar sized strip of copper would bend; and, like it, will keep the form into which it is bent, and will not scratch glass, so that the steel by this treatment has become extremely flexible and soft.

Lastly, take the remaining strip of suddenly quenched steel, polish one of its surfaces with emery paper, then let the end of a large iron poker be heated bright red-hot, and afterwards be supported horizontally upon a brick or tile, placed on a table near the light; lay the strip of steel, with its polished surface uppermost, on the red-hot poker in the direction of its length; in the course of a few seconds the steel will present a curious display of colors, commencing with a straw tint, which gradually deepens to a brown, next to red, with streaks of purple, and ultimately to fine blue; let it be removed and allowed to cool. When cold it will be found to bend with readiness, and to fly back to its original straight form when the bending force is removed. It admits of being scratched with a piece of the brittle, hard strip; so that by this treatment the steel has become less hard than it was, and also regains its elasticity, or technically, it has acquired "spring temper."

The colors that appear upon steel, during the process of tempering, depend upon its iron sustaining slight oxidation, and is therefore rendered capable of decomposing light and of reflecting some of its chronic rays, or their mixtures; for when polished steel is heated out of the contact of the air, it retains its peculiar lustre and only reflects white light, yet it becomes perfectly tempered to any required extent.

The chemist has accurately determined the degree of heat by which steel may be suitably tempered for various implements, and has communicated another important fact to the artisan, that mercury may be heated to any degree short of its boiling point, so that a thermometer introduced into it will denote

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the temperature at which any given temper will be acquired. The best temper for penknives is attained at the straw color. This appears at 450 degrees; accordingly, the mercury is heated to such temperature, and introducing two or three hundred hard steel blades, they will be effectually and simultaneously tempered without involving the tedious necessity of watching the appearance of the straw color upon each individual blade, as must be done if they were placed on heated iron.

The tempering of steel, therefore, consists in reducing its excessive hardness to a moderate degree, by gentle heating, which also restores its toughness and elasticity.

The various colors that announce its fitness for cutting instruments, and the temperature at which they appear, if it be heated in air, or at which temper is conferred, if it be heated under mercury, are hereby subjoined;

At 430 degs., very faint yellow, for lancets.

At 450 degs., pale straw, for razors and scalpels.

At 470 degs., full yellow, for pen knives.

At 490 degs., brown, for scissors and chisels, for cutting iron.

At 510 degs., red with purple spots, for axes and plane-irons.

At 51o, purple, for table-knives and large shears.

At 55 degs., bright blue, for swords, watch and bell springs.
At 560 degs., full blue, for daggers and fine saws.

At 600 degs., dark blue, or almost black, the softest gradation for hand and pit saws.

Steel, if heated still further, becomes perfectly soft.

The ordinary bar iron of Sweden and England, when converted by cementation into steel, exhibits upon its surface numerous small warty points, but few or no distinct viscular eruptions; whereas the Dannemord and the Ulverstone steel present, all over the surface of the bars, well raised blisters, three eighths of an inch in diameter, horizontally, but somewhat flattened at the top. Iron of an inferior description, when highly converted in the cementing-chest, becomes gray on the outer edges of the fracture; while that of the Dannemord acquires a silver color and lustre on the edges, with crystalline facets within. The highly converted steel is used for tools that require to be made very hard; the slightly converted, for softer and more elastic articles, such as springs and sword blades.

One of the greatest improvements which this valuable modification of iron has ever received is due to the late Mr. JOSIAH M. HEATH, who, after many elaborate and costly researches, discovered that, by the introduction of a small portion, one per cent., and even less, of carburet of manganese into the melting pot along with the usual broken bars of blistered steel, a cast steel was obtained after fusion, of a quality very superior to what the bar steel would have yielded without the manganese, and, moreover, possessed of the new and peculiar property of being weldable either to itself or to wrought iron. He also found that a common bar steel, made from an inferior mark or quality of Swedish or Russian iron, would, when so treated, produce an excellent cast steel. One immediate consequence of this discovery has been the reduction of the price of good steel in the Sheffield market by from thirty to forty per cent., and likewise the manufacture of table-knives of cast steel, with iron tangs welded to them; whereas, till Mr. HEATH's invention, table-knives were necessarily made of shear-steel, with unseemly wavy lines in them because cast steel could not be welded to the tangs.

So great is the affinity of iron for carbon, that in certain circumstances, it will absorb it from carburetted hydrogen, or coal gas, and thus become converted into steel. Mr. Mackintosh, of Glasgow, obtained a patent for making steel. His furnace consists of one cylinder of bricks built concentrically within another. The bars of iron are suspended in the innermost, from the top; a stream of purified coal gas circulates freely around, entering below and creeping slowly above, while the bars are maintained in a state of bright ignition by a fire burning in the annular space between the cylinders. This steel

so produced is of excellent quality; but the process does not seem to be so economical as the ordinary cementation with charcoal powder.

All the artificial alloys of silver with steel, of which so much has been said, are not fit for any thing, and are never met with in commerce.

MANUFACTURE OF BAR-IRON.

Mr. W. Clay, of Liverpool, has patented some improvements in manufacturing bar-iron; that invention relates to the employment of rolling pressure for the conversion of bar-iron of various sectional figures, as, for example, plain, straight, square bars, or bars of angle iron, or T or channel grooved or trough iron, into taper bars, or bars which, in their cross-section, gradually diminish or increase from one point of their length to another, the object being to impart to bars of iron so made different strengths or powers of resistance at different points, and thereby to adapt rolled metal to various uses, where greater strength or rigidity is required at one point than at another. This invention also relates to the adaptation of rolling pressure to the formation of bars with sudden as well as gradual irregularities of depth or thickness, by which means it is proposed to form projections, protuberances, or indentions on or in the bars at different points, according to the particular purposes for which the iron may be required. Instead of allowing the top roll to rise gradually in its bearings, and thus afford increasing space between the rolling surfaces (as in his patent of Dec. 16, 1848), Mr. Clay adjusts the rolls to the work they have to perform, and keeps them to that position until the operation is completed, his object being to produce a class of work, the irregularity in the section of which is too great to permit of its being manufactured with facility by the rising roll process. For forming a taper on the extremity of bars suitable for railway "points," he sets the rolls to a distance apart that will correspond with the greatest depth which the formed bar is required to measure, say, for example, three inches; and assuming also, for example, that the extremity of the bar is to be tapered down to, say, one inch in depth, he provides a plate of iron or steel of a taper form, and of a thickness corresponding exactly with the diminution of thickness required in the end of the bar under operation. This plate he takes, in its cold state, and places over the end of the bar of red-hot metal, and then passes the two between the rolls. The taper plate acting as a filling piece, or as an eccentric projection on one of the rolls would act, enables the rolls to put a severer pressure on the bar at the part overlaid by the plate, and thus by simple rolling in an ordinary rolling mill a tapered bar may be produced.

The application of this principle of rolling may be further extended by giving to the contact face of the overlying plate such projections or indentations (whether gradual or sudden) as circumstances may require, such projections or indentations corresponding to, or rather forming a counterpart of the figure to which the contact surface of the bar is required to be reduced. A plate thus formed, being placed over a heated bar of inetal, and submitted with it to the pressure of a pair of rolls, will leave the counterpart impression of its face upon the heated bar of metal. In like manner, when projections or indentations are required on opposite sides of the bar, as will be the case when rolling the spokes for railway wheels, Mr. Clay proposes to enclose the metal to be rolled (the same having been previously heated) between two suitably shaped pressure plates, and then to submit the pile to the rolling pressure.

In this way it will be obvious that he can reduce to unequal thicknesses not merely flat bars or plates of iron, but also angle iron and metal bars, having a concave or convex surface. The patentee claims the imparting a rolling pressure to the bar-iron, in the manner and for the purpose above set forth.

ON THE FORMATION OF BRASS BY GALVANIC AGENCY.

Copper is more electro-negative than zinc, and separates more easily from its solutions than a metal less negative. If then, in order to obtain a deposit