CHAPTER IV

STEEL AND ITS USES

Tempering, Hardening, Testing.

Extracts from a lecture by Henry Seebohm, of Sheffield, Eng.

I fear that the advantages supposed to be derived from the use of manganese in the manufacture of cast-steel are to a large extent illusory. I have frequently conversed with consumers of steel who knew the trade before the introduction of spiegel iron into Sheffield, and it is remarkable how many of them expressed the opinion that the crucible cast-steel now in use is not so good as it was when they were young. Something may, perhaps, be allowed to the illusions of youth. But, nevertheless, I am convinced there is truth in the opinion that the quality of cast-steel has degenerated. In the present day we sacrifice much to appearances. For my part, I always distrust a bar of steel that has not a “seam” or a “roak” in it. The introduction of manganese into cast-steel is a rough-and-ready way of obtaining soundness at the expense of quality, instead of obtaining it by the tedious care and attention which the steel melter who knows his business gives to each individual crucible.

The question that should come before the consumer of cast-steel is the percentage of carbon which he wishes it to contain. When I first began business the “temper” of steel, or the percentage of carbon which it contained, was concealed from the consumer. The despotic sway of the rule of thumb was absolute. If the consumer discovered that chisel steel contained less carbon than tool steel he owed his discovery entirely to his own wit. My firm was the first to take the consumer into our confidence, and the success which has attended our efforts, and the extent to which our labels have been imitated, have completely justified our act. We have always labeled the steel we supplied to consumers with the percentage of carbon it contained, and the purposes to which, in our opinion, steel containing such percentage of carbon was applicable. The following is a list of the most useful “tempers” of cast-steel:

Razor Temper (one and a half per cent carbon).—This steel is so easily burnt by being overheated that it can only be placed in the hands of a very skillful workman. When properly treated it will do twice the work of ordinary tool steel for turning chilled rolls, etc.

Saw-file Temper (one and three-eighths per cent carbon).—This steel requires careful treatment, and although it will stand more fire than the preceding temper should not be heated above a cherry red.

Tool Temper (one and one-fourth per cent carbon).—The most useful temper for turning tools, drills and planing-machine tools in the hands of ordinary workmen. It is possible to weld cast-steel of this temper, but not without care and skill.

Spindle Temper (one and one-eighth per cent carbon).—A very useful temper for mill-picks, circular cutters, very large turning tools, taps, screwing dies, etc. This temper requires considerable care in welding

Chisel Temper (one per cent carbon).—An extremely useful temper, combining, as it does, great toughness in the unhardened state, with the capacity of hardening at a low heat. It may also be welded without much difficulty. It is, consequently, well adapted for tools, where the unhardened part is required to stand the blow of a hammer without snipping, but where a hard cutting edge is required, such as cold chisels, hot salts, etc.

Set Temper (seven-eighths per cent carbon).—This temper is adapted for tools where the chief punishment is on the unhardened part, such as cold sets, which have to stand the blows of a very heavy hammer.

Die Temper (three-fourths per cent carbon).—The most suitable temper for tools where the surface only is required to be hard, and where the capacity to withstand great pressure is of importance, such as stamping or pressing dies, boiler cups, etc. Both the last two tempers may be easily welded by a mechanic accustomed to weld cast-steel.

We may divide consumers of steel into three classes. First, those who use their own judgment of what percentage of carbon they require, and instruct the manufacturer to send them steel of a specified temper; second, those who leave the selection of the temper to the judgment of the manufacturer, and instruct him to send them steel for a specified purpose; and third, those who simply order steel of a specified size, leaving the manufacturer to guess for what purpose it is required. Fortunately, the size and shape generally furnish some clue to the purpose for which it is likely to be used. For example, oval steel is almost sure to be used for chisels, and small squares for turning tools. One and one-fourth square may be used for a turning tool or a cold set, one and one-fourth round for a drill or a boiler-cup, and the manufacturer has to puzzle his brains to discover whether the chances are in favor of its going into the lathe-room or the blacksmith’s shop. It cannot too often be reiterated of how much importance it is, when ordering steel, to state the purpose for which it is going to be used.

When the steel has arrived in the user’s hands, the first process which it undergoes is the forging it into the shape required. This process is really two processes. First, that of heating it to make it malleable, and second, that of hammering it, while it is hot, into the required shape. The golden rule in forging is to heat the steel as little as possible before it is forged, and to hammer it as much as possible in the process of forging.

The worst fault that can be committed is to overheat the steel. When steel is heated it becomes coarse grained; its silky texture is lost, and it can only be restored by hammering or sudden cooling. If the temperature be raised above a certain point, the steel becomes what is technically called “burnt,” and the amount of hammering which it would require to restore its fine grain would reduce it to a size too small for the required tool, and the steel must be condemned as spoiled. Overheating in the fire is the primary cause of cracking in the water.

The process of hammering or forging the steel into the shape required has hardened the steel to such an extent as to make the cutting impossible or difficult; it must consequently be annealed. This process, like the preceding one, is a double process. The steel must be reheated as carefully as before, and afterward cooled as slowly as possible.

We now come to the culminating point in our manufacture, where the invaluable property which distinguishes steel from wrought iron or cast metal is revealed.

The part of the tool required to be hardened must be heated through, and heated evenly, but must on no account be overheated. Our tool must be finished at one blow—the blow caused by the sudden contraction of the steel produced by its sudden cooling in the water—and if this blow is not sufficient to give to the steel a fine grain and silky texture—if, after the blow is given, the fracture, were it broken in the hardened part, should show a coarse grain and dull color, instead of a fine grain and glossy luster, our tool is spoiled, and must be consigned to the limbo of “wasters.” The special dangers to be avoided in hardening each kind of tool must be learned by experience. Some tools will warp or “skeller,” as we say in Yorkshire, if they are not plunged into the water in a certain way. Tools of one shape must cut the water like a knife; those of another shape must stab it like a dagger. Some tools must be hardened in a saturated solution of salt, the older the better, while others are best hardened under a stream of running water.

In some tools, where the shape necessitates a great difference in the rapidity of cooling, it is wise to drill holes in the thicker parts where they will not interfere with the use of the tool—holes which are made neither for use nor ornament, but solely with a view of equalizing the rapidity of the various parts, so as to distribute the area of tension and thus lessen the risk of cracking in hardening. So many causes may produce water-cracks that it is often difficult to point out the precise cause in any given case. Perhaps the most common cause is overheating the steel in one or more of the processes which it passes through in the consumers’ hands, or it may have been overheated in the process of forging, or rolling it into the dimensions required while in the hands of the manufacturer. A second cause may be found in the over-melting, or too long boiling of the steel, causing it to part with too much of its confined carbonic acid, a fault which may be attributed to the anxiety of the manufacturer to escape honeycomb in the ingot. A third cause may be sometimes discovered in the addition of too much manganese, added with the same motive. A fourth cause may, curiously enough, prove to be a deficiency of carbon, while, in some cases, too much will produce the same effect. A fifth cause may be one which, as a steel manufacturer, I ought to mention in a whisper—the presence of too much phosphorus in the steel; but, after all, this may not be the fault of a greedy manufacturer, who wants to make too great a percentage of profit. It might be the fault of a stingy consumer, who begrudges him the little profit he makes. You may depend upon it there is nothing so dear as cheap steel. It must be more economical to put five shillings’ worth of labor upon steel that costs a shilling, to produce a tool that lasts a day, than to put the same value of labor upon a steel that costs only ninepence, to produce a tool that only lasts half a day.

Our difficulties are not quite over when the process of hardening has been successfully accomplished. Our steel was originally lead; it has now become glass. To attain its proper condition our tool must pass through the final process—that of tempering.

If you heat a piece of hardened steel slightly, and allow it to cool again, it becomes tempered. It suddenly changes from glass to whalebone; and in the process of changing its nature, it fortunately changes its color, so that the workman can judge by the hue of the color the extent of the elasticity which it has acquired, and can give to each tool the particular degree of temper which is most adapted to its special purpose. The various colors through which tempered steel successfully passes are as follows: Straw, gold, chocolate, purple, violet and blue. Of course, in passing from one color to another, the steel passes through the intermediate colors. It really passes through an infinite series of colors, of which the six above mentioned are arbitrarily selected as convenient stages.

It is supposed that the maximum of hardness and elasticity combined is obtained by tempering down to a straw color. In tempering steel regard must be had to the quality most essential in the special tool to be tempered; for example, a turning tool is required to be very hard, and is generally taken hot enough out of the water to temper itself down to a degree so slight that no perceptible color is apparent, while a spring is required to be very elastic, and may be tempered down to a blue. If you ask me to give you a scientific explanation of the process of tempering steel, I must confess my absolute ignorance.

Hardening in oil is another mode of treating steel, which appears to a certain extent to attain by one process the change from lead into whalebone without passing through the intermediate glass stage, and is of great value for certain tools.

There are many kinds of steel to which your attention should be called, but which can only obtain from me the briefest mention. A special steel for taps, called mild-centered cast-steel, is made by converting a cogged ingot of very mild cast-steel, so that the additional carbon only penetrates a short distance. These bars are afterward hammered or rolled down to the size required, and have the advantage of possessing a hard surface without losing the toughness of the mild center.

Another special steel, somewhat analogous to mild-centered cast-steel, is produced by melting a hard steel on to a slab of iron, or very mild steel heated hot enough to weld with the molten steel, so that a bar may be produced, one-half of which is iron and the other half steel, or three-fourths iron and one-fourth steel, as may be required.

A third kind of special steel, which is used for turning tools for chilled rolls, magnets and some other purposes, is made by adding a certain percentage of wolfram, or, as the metal is more generally called, tungsten, sometimes with and sometimes without carbon, sometimes to such an extent that it can be used without hardening in water. Special steel of this kind is the finest-grained that can be produced, but it is so brittle that in the hands of any but exceptionally skilled workmen it is useless. The addition of chromium, instead of wolfram, has somewhat the same effect.

TESTING.

It is much to be regretted that no easy method of testing cast-steel has been invented. The amount of breaking strain and the extent of contraction of the area of the fracture are all very well for steel which is not hardened, and not required to be used in a hardened state, but for hardened and tempered steel it is practically useless. It is very difficult to harden and temper two pieces of steel to exactly the same degree. A single test is of comparatively small value, as a second-rate quality of steel may stand very well the first time of hardening, but deteriorates much more rapidly every time it is rehardened than is the case with high quality steel. Nor am I at all sure that the breaking strain is a fair test of the quality of steel. For many tools the capacity to withstand a high amount of breaking strain slowly applied is not so much required as its capacity to withstand a sudden shock. The appearance of the fracture is very illusory. The fineness of the grain and the silkiness of the gloss is very captivating to the eye, but it can be produced by hammering cold. The consumer of steel may be enraptured by the superb fracture of a bar of steel; but, after all, this is only a dodge, depending upon the inclination of the axis of the revolving hammer to the plane of the anvil. The practical consumer of steel must descend from the heights of art and science and take refuge in the commonplace of the rule of thumb, and buy the steel which his workmen tell him is full of “nature” and “body.”

Hints Regarding Working Steel.

Salt water is no more likely to crack steel than fresh or soft, if the steel has been properly, uniformly, heated. Brine will produce a greater degree of hardness at the proper heat, other things being equal.

Steel requires the same conditions for annealing, whether in bulk, ponderous or otherwise. The sine qua non is, heat uniformly to proper heat and as soon as homogeneously saturated (not super-saturated) permit to cool as slowly and uniformly as practicable.

My experience says: Harden in every case where practicable under a stream of cold water, taking care that the contact is perfect and directed to the locale requiring the greatest degree of hardening. It is almost always prudent to move the article constantly, if only slightly.

Wherever water is in impinging motion it is, of course, more rapidly changing its heated for a colder co-efficient, or successive heat extractor, we will call it, and the more extractors receiving heat the quicker the locality is refrigerated and fixed, consequently the hardest.

Very few, if any, drop hammer dies, if properly hardened, require a subsequent tempering.

I have known good gray, or, in some cases, white cast-iron, capable of doing twenty times the amount of work of any kind of steel tried.

My way is to heat all ordinary brands of “tool cast-steel” very slowly (and if practical) in a COOL fire, to commence with, gradually letting (by draught rather than blast) both fire and steel increase in temperature together, to as low red as is necessary.—By W. DICK.

The Warping of Steel During the Hardening Process.

In heating steel to harden it, especial care is necessary, particularly when the tool is one finished to size, if its form is slight or irregular, or if it is a very long one, because unless the conditions both of heating and cooling be such that the temperature is raised and lowered uniformly throughout the mass, a change of form known as warping will ensue. If one part gets hotter than another it expands more, and the form of the steel undergoes the change necessary to accommodate this local expansion, and this alteration of shape becomes permanent. In work finished and fitted this is of very great consideration, and, in the case of tools, it often assumes sufficient importance to entirely destroy their value. If, then, an article has a thin side, it requires to be so manipulated in the fire that such side shall not become heated in advance of the rest of the body of the metal, or it will become locally distorted or warped. If, however, the article is of equal sectional area all over, it is necessary to so turn it in the fire as to heat it uniformly all over; and in either case care should be taken not to heat the steel too quickly, unless, indeed, it is desirable to leave the middle somewhat softer than the outside, so as to have the outside fully hardened and the inside somewhat soft, which will leave the steel stronger than if hardened equally all through. Sometimes the outside of an article is heated more than the inside, so as to modify the tendency to crack from the contraction during the quenching; for to whatever degree the article expands during the heating, it must contract during the cooling. Hence, if the article is heated in a fluid, it may often be necessary to hold the article, for a time, with the thick part only in the heating material; but in this case it should not be held quite still, but raised and lowered gradually and continuously, to insure even heating.

Pieces, such as long taps, are very apt to warp both in the fire and in the water. In heating, they should rest upon an even bed of coked coal, and be revolved almost continuously while moved endways in the fire; or when the length is excessive, they may be rested in a heated tube so that they may not bend of their own weight. So, likewise, spirals may be heated upon cylindrical pieces of iron or tubes to prevent their own weight from bending or disarranging the coils.

If a piece is to be hardened all over, it must be occasionally turned end for end, and the end of the holding tongs should be heated to redness or they will abstract the heat from the steel they envelop. Very small pieces may be held by a piece of iron wire or heated in a short piece of tube, the latter being an excellent plan for obtaining a uniformity of heat, but in any event the heating must be uniform to avoid warping in the fire, and, in some cases, cracking also. This latter occurs when the heating takes place very quickly and the thin parts are not sufficiently heated to give way to accommodate the expansion of the thick ones. The splitting or cracking of steel during the cooling process in hardening is termed water cracking, and is to be avoided only by conforming the conditions of cooling to the size and shape of the article.

Experiments have demonstrated that the greater part of the hardness of steel depends upon the quickness with which its temperature is reduced from about 500° to a few degrees below 500°, and metal heated to 500° must be surrounded by a temperature which renders the existence of water under atmospheric pressure impossible; hence, so long as this temperature exists the steel cannot be in contact with the water, or, in other words, the heat from the steel vaporizes the immediately surrounding water. As the heated steel enters the water the underneath side is constantly meeting water at its normal temperature, while the upper side is surrounded by water that the steel has passed by, and, to a certain extent, raised the temperature of. Hence, the vapor on the underneath side is the thinnest, because it is attacked with colder water and with greater force, because of the motion of the steel in dipping. Suppose, now, we were to plunge a piece of heated steel into water, and then slowly move it laterally, the side of it which meets the water would become the hardest, and would be apt to become concave in its length.

From these considerations we may perceive how important a matter the dipping is, especially when it is remembered that the expansion which accompanies the heating is a slow process compared to the contraction which accompanies the cooling (although their amounts are, of course, precisely equal), and that while unequal expansion usually only warps the article, unequal contraction will in a great many, or, indeed, in most cases, cause it to crack or split.—By JOSHUA ROSE, M. E.

Tempering Steel.

I have read with considerable interest the different processes for tempering steel, and the different treatments that have appeared from time to time in mechanical journals. It always seemed to me the object to be sought for is to cool the steel as soon as possible after it has been heated to the well known cherry red, and, in doing so, the different solutions offered for a cooling bath are as numerous as the recipes for a toothache. Mercury, no doubt, makes the best bath, and salt water, for many purposes, is equally as good. But one object I have observed in quenching steel, is the time required for reducing the heat. For some moments the heated steel shows its cherry color through the cooling bath. Mercury, being the best conductor of heat, takes away the heat the fastest and hardens it the hardest. If there were any way in which the cold water could be brought in contact with the metal, its heat would the sooner be removed. Warm water hardens almost as well as cold, except for light work. This may be owing to the jacket formed about the heated steel, which protects the steel from losing its heat. This is more particularly noticed in hardening the face of a hammer so that it will not settle in the center, or cave off around its edge. In plunging it into the bath, the center of the face is, to a certain extent, protected by the heat from the outer edge, and remains the softest. The drawing process or tempering being governed by the color of the oxidization that appears on the polished surface, there is no way to distinguish the hard places from the soft that were produced in hardening; and without further comment, will state that the process of hardening by cooling with water that is brought in close contact with the heated surface by pressure, promises well, and should find its way more effectually into general use. The writer remembers very well when at work in a shop close by a reservoir, where a stream of water rushing through an orifice, under a head of twelve feet or more, was always ready for quenching steel for the purpose of hardening. Hammers were heated as near the right temperature as was thought best and held under the stream where the water would strike square upon the face of the hammer, removing the heat with great rapidity, the heated liquid passing off out of the way and the cooler taking its place, and, owing to the great pressure, the film of vapor that might otherwise be formed between the heating and cooling surfaces is broken up. Smooth metallic surfaces, when heated to a low red heat, are protected from coming in contact with a liquid by the intervening film of steam which gives an imperfect in hardening, and is known as the spheroidal state of liquids, as observed when cooling sheets of iron by pouring water upon them, the liquid will run about in large drops without breaking up or boiling. Steel is hardened to a remarkable degree by being forced in contact with almost any cold substance. A flat drill that has been heated at the point, and driven into a lump of cold lead, is as hard as if quenched in a bath of cold water. Any way to remove the heat is all that is required for hardening, and the sooner it is removed the better, and in chilling with cold water it is necessary that the steel should be moved about to break up the film, and to keep in contact with the cooling liquid. I have felt an interest in the matter of tempering steel, and cannot but feel that this state of things in regard to the close communion between heated metals and their cooling solutions should be more fully understood.—Cotton, Wool and Iron.

Another Method of Tempering Steel.

It is desirable to obtain any degree of hardness by a single process if possible. In some cases, by heating a known quantity of steel to a definite temperature and quenching it in liquid maintained at about an even temperature, the color is becoming dispensed with, the conditions of heating and cooling being varied to give any degree of hardness. Another and a very desirable method of hardening and tempering, is to heat in a flue of some kind, maintained at the required temperature over the fire, and after quenching, instead of applying the color test, provide a tempering bath composed of some substance heated to a temperature of from 430° to 630°. By placing the articles (after hardening them) in the tempering bath and heating it to a temperature equal to the color of the temper required, we have but to cease heating the tempering bath when a thermometer marks the required temperature. A uniform degree of temper will be given to all the articles, and the operation will occupy much less time than would tempering by the color test, because a liquid is much more easily kept at an equal temperature throughout its mass than are the heated sand or hot pieces of metal resorted to in tempering by the color test. Another method of tempering is to heat the steel to a definite temperature and cool or quench it in a liquid having sufficient greasiness or other quality which acts to retard its retraction of the heat from the steel and thus give a temper at one operation. As an example of this kind of tempering, it is said that milk and water mixed in proportions determined by experiment upon the steel for which it was employed, has been found to give an excellent spring temper. Such tempering carefully conducted may be of the very best quality. A great deal, however, in this case depends on the judgment of the operator, because very little variation in heating the steel or in the proportions of milk to water produces a wide variation in the degree of temper. If, on trial, the temper is too soft, the steel may be made hotter or more water added to the milk. If the steel was heated as hot as practicable without increasing the danger of burning it, more water must be added, while if the steel was made red-hot without being hot enough to cause the formation of clearly perceptible scale, the steel may be heated more. It is desirable in all cases, but especially with a high quality of steel, not to heat it above a blood-red heat, although sheer and spring steels may be and often must be made hotter in order to cause them to harden when quenched in water.

Hardening and tempering steel, as applied to cutting tools, are much more simple than when the same operations are required to give steel elasticity as well as durability of form or to give durability to pieces of slight and irregular form of sufficient hardness to withstand abrasion. One reason of this is that for tools a special and uniform quality of steel is readily obtainable, which is known as tool steel. Special sizes and grades are made to suit the manufacture of any of the ordinary forms of tools.

As a rule, the steel that shows a fracture of fine, dull grain, the face of the fracture being comparatively level, is of better quality than that showing a coarse or granulated surface, brightness denoting hardness, and fibrousness, toughness.

Very few steels are as yet sufficiently uniform to render it practicable to employ an unchangeable method of tempering, and to this fact is largely due the use of particular brands of steel.

In tempering steel, regard must be had to the quality most essential in the special tool to be tempered. A turning tool is required to be very hard and is often taken out of the water hot enough to temper itself down to a degree so slight that no color is perceptible, while a spring is required to be very elastic and may be tempered down to a blue.

A scientific explanation of the process of tempering steel has yet to be given without mystifying one by talking unintelligibly about molecular rearrangement and crystalline transportations.

Working Steel.

In making steel tires blacksmiths generally heat them too much. A deep cherry-red is hot enough. Of course you can’t make much headway in hammering, but you should heat oftener. It is better to spend time in heating often than to burn the steel, spoil the job and get nothing for it. When steel has been hammered cold and gets black it should never be heated hot enough to raise a scale, because this would open the pores and render it worthless for anything requiring tempering. Heat just to a low cherry-red and draw your temper accordingly. Some smith may say: “It wouldn’t be hard enough.” Don’t be afraid of that; it will be hard enough for anything.—By BENNINGER & SON.

Working and Tempering Steel.

To work steel never heat above a light cherry-red for hammering, then hammer light and quick until near black, as this improves the steel and will make tools that will do more than double the work than if not so treated. The hardness of steel is governed entirely by the heat when it is dipped in water; for instance, a piece of steel dipped at a bright cherry color and drawn to a straw, will be very much harder than a piece heated to a dark cherry-red and then dipped and drawn to a straw. Try it.

The forging, hardening and tempering of steel is an art that but few understand, as its knowledge is only gained by experience, and but few ever give its secrets to others; yet in a few words I will try to give the principal elements to workers of steel, which if followed will save you many losses, and give you a reputation for working steel that will ensure you good and serviceable tools, as well as increase your gains.

Please remember that the heat at which steel is worked and hardened are two of the vital elements to produce good and serviceable tools. If heated above a light cherry-red, some of the vitality of the steel is destroyed, and it would in heating too many times return to iron. If heated too hot when hardening it would fly to pieces, destroying your labor and steel as well as giving you a poor reputation.

Remember also to hammer your work lightly at a low heat, as this improves chisels, drills, lathe tools, and edge tools most wonderfully; also take as few heats as possible, as overheating and too frequent heating reduces the steel to iron by destroying the carbon.

To harden taps, rimmers, chisels and drills, always dip them slowly to the depth desired in as near a vertical line as you can by the eye and hand, then move in a circular position until cold, but never any deeper in the water than first dipped, as this prevents them from cracking, which they would be likely to do if held perfectly still and the water formed a line around them. Do not change the water in which you temper, but as it wastes fill up the tank. If you are obliged to use fresh water always heat a piece of iron to put into it and bring it to such a warmth as is perceptible to the hand, as steel is liable to crack when dipped into cold water, When you have heated your article to be tempered take it from the fire and examine to see if any flaws are observable in the steel, as this will prevent your having poor pieces of steel laid to your carelessness in hardening.

In cutting up steel a thin, sharp chisel should be used, as a blunt one is liable to splinter or crack the bar, which will not be seen until it is tempered and then the labor is lost with the steel.

Colors of different articles for use.—Taps should be hardened and then brightened by rubbing emery and oil on the clearance, and then draw on a hot plate or in a heated ring to a dark straw color.

Dies should be a bright straw color and drawn on a hot plate or in sand.

Drills for iron should be a dark straw on the cutting part and the rest a blue.

Chisels for iron should be violet color; for cutting stone a purple is required.

Milling cutters should be of a yellowish white. Gear teeth cutters the same color. The usual way to dip these is to have a rod with three prongs to pass through the hole after it is heated to dip with, lower slowly until all the cutter is under the water about two inches, then move in a circular position until thoroughly cold, remembering that a great many things break by taking from the water before they are cold, especially large pieces of steel, as the center retains the heat, and when taken from the water it expands the outside and causes it to crack.

In tempering pieces having a thick and thin edge, always dip the thickest part first. Study the pieces you have to harden and it will help you very much. Large centers in work for tempering should be avoided, as they are liable to cause the end to split open.—Iron Trade Review.

Tempering Steel.

Two of the most important processes in blacksmithing, are the hardening and the tempering of steel. Great judgment particularly, as well as experience, is required to temper dies and tools. With good judgment, a person will soon learn to temper; but without good judgment, tempering can never be successfully learned. A man may learn to do one special kind of work, but put him in a large hardware manufacturing establishment, where all kinds of dies and tools are used, with hardly any two requiring the same temper, and without judgment, the difficulties connected with such a position can never be overcome.

To harden and temper a piece of steel, it should always be properly annealed; otherwise it is almost certain to spring or warp. It is a very general idea that you can draw all the temper out of steel, without heating it red hot all over; but such is not the case. Heating the face of a die and covering it up in ashes does not thoroughly anneal it by any means. Possibly in that way you can get it in such a condition that it can be worked; but it will not be very soft, and will not harden and temper as well as if it had been heated all over.

The best way that I ever found to anneal steel (when you do not have a kiln for that purpose) is to heat it all over in a slow charcoal fire; the slower it is heated the better. Do not heat very hot, but all over and all through. Then take it out and cover it up in fine charcoal, and let it remain till cold.

In heating a die for the purpose of hardening, it is not necessary to heat it all over, unless you want to harden it all over. The only way, in my judgment, that dies can be tempered as they should be, is for the one that tempers them to see, from time to time, how they work, as they are being used; and in that way he can tell if they require more or less temper and the particular places where they should be hard or soft.

It is useless for anyone to undertake to tell how to temper everything that is used in a manufacturing establishment; such knowledge can only be acquired by experience, combined with good judgment and mechanical ingenuity. I will try, however, to explain my way of hardening and tempering.

Trip-hammer dies may seem to be very easy to handle, but a blacksmith without experience would meet with many difficulties. Take, for instance, a die seven or eight inches long, one and a half inches thick and four and a half inches wide with several impressions cut in it, leaving several small points which are liable to fly off as soon as they are hardened or when you are drawing the temper. Now, my way to prevent the corners from coming off, and keep the dies straight is this: I heat my die very carefully in a clean charcoal fire, being careful not to get it any hotter than is necessary to have it harden. When the proper heat has been obtained, grasp it with the tongs near one end in such a way that it can be put in the water perpendicularly, and while in the water I turn it to a horizontal position and take it about half-way out, letting it remain until it is cool enough on the face to take out entirely for an instant without permitting the temper to run down. Then I withdraw it and return it to the water several times very quickly until it is cool enough to take out and scour off. The temper can then be drawn to suit, without any danger of the corners flying off.

The object in putting it in the water perpendicularly is to keep it straight; and, as it cools off all alike, when you bring the back out of the water the heat rushes up toward the back, and expands it, taking all the strain off the face of the die and preventing it from breaking.

By plunging it into the water and withdrawing it very quickly, the face of the die has time to get cool gradually, and the corners are thus prevented from flying off.

This process will work well on any dies or tools hardened in this way. I have tried it hundreds of times with the best of success.—By G. B. J.

Tempering Small Articles.

When tempering cold chisels, or any other steel articles, heat to a very dull red and rub with a piece of hard soap, then finish heating and harden in clear, cool water. The potash of the soap prevents the oxygen of the atmosphere from uniting with the steel and forming rust or black oxide of iron. The article will need no polishing to enable the colors to be seen. This will be appreciated when tempering taps, dies or various complex forms not easy to polish. Never “upset” a cold chisel. It is sure death to steel. Many of us have lived on a farm and know something about a bundle of nice, straight, clean straw. If you work it intelligently you can tie it up into stout bands for binding other bundles. You can take hold of the ends of the straw and draw out a handful without harm to the straw. After you have drawn out half that bundle a foot or so, try to drive it back; every blow breaks the straw, cripples and doubles it up, and it will hardly bear its own weight, to say nothing of making a band for other bundles. Just so with steel. If you have a broken chisel to sharpen, draw out and cut off, never upset. It will cripple the fibers just as the straw is crippled when driven endwise.

Make chisels short for hard, rough work. They transmit the power or force of a blow much better. Long chisels are apt to “broom up” on the hammer end, as the long steel through which the blow passes has more chance to absorb the force of the blow.

The harder the metal to be worked, the quicker the blow should be transmitted. Cast-iron works much better with a short steel chisel and light hammer, than if the blow was struck upon a very long chisel with a heavy wooden mallet. —Age of Steel.

Tempering Steel.

I have never used any mercury in tempering but have no doubt it answers the purpose. I was one of the first blacksmiths in this country who worked cast-steel. The boss under whom I learned the trade made it a part of his business to teach country blacksmiths how to put cast-steel in axes and how to weld and temper it. He welded with borax melted into a kind of hard glassy substance.—By C. W.

Tempering Steel with Low Heat.

Some curious statements on tempering steel are made in a paper published in Dingler’s Polytechnic Journal, vol. 225, by Herr A. Jarolimek, “On the Influence of the Annealing Temperature upon the Strength and the Constitution of Steel.” Hitherto it has been generally considered that to obtain a specified degree of softness it is necessary to heat the hard steel to a particular annealing color—that is to say, to a definite temperature—and then allow it to rapidly cool. Thus, for example, that steel might anneal—be tempered—yellow, it has to be heated to 540 deg. and the supposition was formed and acted upon that it must be allowed only a momentarily subjection to this temperature. Herr Jarolimek says the requisite temper, which is obtained by momentarily raising the temperature to a particular degree, can also be acquired by subjecting the steel for a longer time to a much lower temperature. For example, the temper which the annealing color—yellow—indicates, can be obtained by exposing the hard steel for ten hours to 260 degrees of heat; in other words, by placing it in water rather above the boiling point.

To Temper Steel Very Hard.

As hardness of steel depends on the quickness with which it is cooled, there are better materials than water, which gives an unequal temper; besides the steam bubbles developed interrupting contact; water is also a bad conductor of heat, and if the bubbling and heat did not put it in motion, it would be unfit for hardening. Water with plenty of ice in it gives a hard temper; small tools may be stuck into a piece of ice, as jewelers insert them in a piece of sealing wax. Oil is also used by them as being better than water, as it does not evaporate so easily. The Damascus steel blades are tempered in a small current of cold air passing through a narrow slit; this gives a much more uniform and equal temperature than water. But the most effective liquid is the only liquid metal—mercury. This being a good conductor of heat, in fact the very best liquid conductor, and the only cold one, appears to be the best one for hardening steel-cutting tools. The best steel, when forged into shape and hardened in mercury, will cut almost anything. We have seen articles made from ordinary steel, which have been hardened and tempered to a deep straw color, turned with comparative ease with cutting tools from good tool steel hardened in mercury. Beware of inhaling the vapor while hardening.

Hardening Steel.

Often when great care has been taken in heating a straight piece of steel, and it is put into water or other hardening compound, it comes out crooked; in this case the trouble is entirely in the forging. I will give my reasons for this statement.

Long pieces of steel, such as reamers for boring boxes for axles, are generally forged under a trip hammer. We will suppose the piece of steel to be forged is evenly heated through. The blacksmith takes the bar in one hand, and in the other his hammer, and the helper holds his sledge ready for business. The smith turns the bar back and forth, never turning it entirely over. Now, the hammer and the sledge will draw out the fiber or grain of the steel faster than the anvil. The steel is unevenly forged, and very likely will not be straight, but will be made straight across the anvil. Heat this piece of steel as evenly as possible, and put it into water or other compound, and it will very likely be crooked when hardened.

If a piece of steel is heated evenly, and hammered equally as many blows on all sides, and if, when crooked, while forging, it is straightened by hammering, and care has been used in heating, it will generally come out straight, providing the same care has been observed before it comes to the blacksmith.—By C.

Case-Hardening Steel or Iron.

I think the best and simplest method of case-hardening iron is to use prussiate of potash. It is a yellow substance that comes in the shape of flaky, shining flat lumps. Pulverize it till it is as fine as flour; heat the article to be hardened to a deep red, and put on the potash just where you want it to be hard. Then put it back in the fire, heat to a deep red and plunge into cold water.—By J. P. B.

How Damascus Sword Blades Were Tempered.

Perhaps the best method which has ever been discovered for tempering steel, resulting in hardness, toughness and elasticity combined, is that followed in hardening the blades of the famous Damascus swords. The furnace in which the blades were heated was constructed with a horizontal slit by which a current of cold air from the outside entered. This slit was always placed on the north side of the furnace and was provided on the outside with a flat funnel-shaped attachment by which the wind was concentrated and conducted into the slit. The operation of tempering the blades was only performed on those days of winter when a cold strong north wind prevailed. The sword blade when bright red-hot was lifted out of the fire and kept in front of the slit and by this means was gradually cooled in the draft of air. It acquired the proper degree of temper at the single operation.

To Harden Steel.

A very fine preparation for making steel very hard is composed of wheat flour, salt and water, using say two teaspoonsful of water, one-half a teaspoonful of flour, and one of salt; heat the steel to be hardened enough to coat it with the paste—by immersing it in the composition—after which heat it to a cherry-red and plunge it in cold, soft water. If properly done, the steel will come out with a beautiful white surface. It is said that Stubb’s files are hardened in this manner.

Tempering Steel Springs.

The hardening and tempering of springs whose coils are of thick cross-section is performed at one operation as follows: The springs are heated in the furnace or oven described, and are first immersed for a certain period in a tank containing fish oil (obtained from the fish “Moss Bunker,” and termed “straights”), and are then removed and cooled in a tank of water. The period of immersion in the oil is governed solely by the operator’s judgment, depending upon the thickness of the cross-section of the spring coil, or, in other words, the diameter of the round steel of which the spring is made. The following, however, are examples:

 Number of coils in spring53/4
 Length of the spring6 inches.
 Outside diameter of coils43/4 inches.
 Diameter of steel1 inch.

The spring was immersed in the oil and slowly swung back and forth for twenty-eight seconds, having been given thirty-five swings during that time. Upon removal from the oil the spring took fire, was re-dipped for one second, and then put in the cold water tank to cool off.

Of the same springs the following also are examples:

  Time of immersion in oilNumber of swings in oil.
  Example.    
 Second36 seconds.46
 Third27 seconds.36
 Fourth38 seconds.40

SIZE OF SPRING.

 Number of coils in the springs6
 Length of the springs9 inches.
 Inside diameter of coils31/4
 Size of steel1 × 11/2 square.
  Time of immersion in oil.Number of swings in oil.
 Example.    
 First9 seconds.12
 Second8 seconds.12
 Third8 seconds.12
 Fourth9 seconds.12
 Fifth9 seconds.12
 Sixth9 seconds.12

To keep the tempering oil cool and at an even temperature, the tank of fish-oil was in a second or outer tank containing water, a circulation of the latter being maintained by a pump. The swinging of the coils causes a circulation of the oil, while at the same time it hastens the cooling of the spring. The water-tank was kept cool by a constant stream and overflow.

If a spring, upon being taken from the oil, took fire, it was again immersed as in the first example.

In this, as in all other similar processes, resin and pitch are sometimes added to the oil to increase its hardening capacity if necessary.

The test to which these springs were subjected was to compress them until the coils touched each other, measuring the height of the spring after each test, and continuing the operation until at two consecutive tests the spring came back to its height before the two respective compressions. The amount of set under these conditions is found to vary from three-eighths of an inch, in comparatively weak, to seven-eighths of an inch for large, stiff ones.

The springs were subjected to a severe test in a machine designed for that purpose, being compressed and released until there was no set under the severest test.

In the following description of the plans adopted by a very prominent carriage-spring maker will also be found a process termed a water-chill temper, which tempers at one process. The steel used by this firm is “Greave’s spring steel.” The spring plates are heated to bend them to the former, which is a plate serving as a gauge whereby to bend the plate to its proper curve.

This bending operation is performed quickly enough to leave the steel sufficiently hot for the hardening; hence the plates after bending are dipped edgeways and level into a tank of linseed oil which sets in a tank of circulating water, the latter serving to keep the oil at about a temperature of 70 degrees when in constant use. About three inches from the bottom of the oil tank is a screw to prevent the plates from falling to the bottom among the refuse sediment.

To draw the temper the hardened springs are placed in the furnace, which has the air-blast turned off, and when the scale begins to rise, showing that the adhering oil is about to take fire, they are turned end for end in the furnace so as to heat them equally all over. When the oil blazes and is freely blazed off, the springs are removed and allowed to cool in the open air, but if the heat of a plate, when dipped in the oil to harden, is rather low, it is cooled, after blazing, in water. The cooling after blazing thus being employed to equalize any slight difference in the heat of the spring when hardened.

The furnace is about ten inches wide and about four inches longer than the longest spring. The grate bars are arranged across the furnace with a distance of three-eighths of an inch between them.

The coal used is egg anthracite. It is first placed at the back of the furnace, and raked forward as it becomes ignited and burns clearly.

For shorter springs the coal is kept banked at the back of the furnace, so that the full length of the furnace is not operative, which, of course, saves fuel. By feeding the fire at the back end of the furnace, the gases formed before the coal burns quickly pass up the chimney without passing over the plates, which heat over a clear fire.

For commoner brands of steel, what is termed a water-chill temper is given. This process is not as good as oil-tempering, but serves excellently for the quality of steel on which it is employed. The process is as follows: The springs are heated and bent to shape on the former plate as before said; while at a clear red heat, and still held firmly to the former plate, water is poured from a dipper passed along the plate. The dipper is filled four or five times, according to the heat of the plate, which is cooled down to a low or very deep red. The cooling process on a plate 11/2 × 1/4 inches occupies about six seconds on an average, but longer if the steel was not at a clear red, and less if of a brighter red when the cooling began, this being left to the judgment of the operator.

Some brands of steel of the Swede steel class, will not temper by the water-chill process, while yet other brands will not harden in oil, in which case water is used to dip the plates in for hardening, the tempering being blazing in oil as described. In all cases, however, steel that will not harden in oil will not temper by the water-chill process. —By JOSHUA ROSE, A.M.

Tempering Small Tools.

I have had a great many years’ experience in the matter of tempering small tools, such as chisels, punches, drills, etc., and I think that I may be able, accordingly, to give some simple directions which will be of use to the trade. Steel for tools of this kind should never be heated beyond a bright cherry-red. The last hammering should be invariably on the flat sides, and at a very low heat; the tool meanwhile being held fairly on the anvil, and blows struck squarely with the hammer. This process is technically known as hammer-hardening, and serves to close the grain of the steel. After this, heat the article slowly and evenly until it shows a cherry-red about one and one-half inches from the point. Immerse the tool edge first into pure cold water, the surface of which is perfectly calm, a short distance, and hold it steadily at that point until the red above the water has become quite dull. Brighten the tool slightly by rubbing on a stone or by any other convenient means, and watch the changes of color which occur. First, blue will appear next to the body of the chisel, then probably brown, after which will come dark straw-color, then light straw-color, and at the edge a quite bright straw-color. Heat from the body of the tool will gradually change the location of these colors. The bright edge will assume a light straw-color; then will follow straw-color, orange, brown, and finally blue.

A word with reference to colors in the matter of tempering. A tool to cut hard cast-iron should be straw-color, or sometimes light straw-color; for soft cast-iron it should be dark straw-color; for wrought-iron, purple; or, if the iron is quite soft, blue may be found hard enough. A chisel treated as last described will wear well and not break easily. Drills may be tempered in the same way as described above. In my own practice, I leave them a shade harder than is required in a chisel. On the other hand punches may be slightly softer for the same work.—By SMALL TOOLS.

To Temper Small Pieces of Steel.

Many blacksmiths are bothered to temper small pieces of steel on account of their springing. My way is to temper them in linseed oil, and they give me no trouble. I make a great many very thin knives.

Take a tin can large enough to insert the steel that you want to temper, say a tall two-quart fruit can, fill it with oil. Do not work your steel too hot, for that will spoil any steel. Temper just the same as you would if you were using water, and I think the result will be satisfactory.—By VOLNEY HESS.

Hardening Thin Articles.

In hardening any article of steel that is thin or light and heats quickly, it is advisable to remove on a grindstone or emery wheel the scale formed in forging before heating. The scale being of unequal density, if it is not removed it is generally impossible to heat evenly; besides, the degree of heat can be better observed if it is removed.

Sword Blades.

Sword blades are made and tempered so that they will chip a piece out of a stone without showing a nick upon their edges, says a gentleman who has been through the great sword manufactory at Soligen, Germany. The steel, he says, is cut from bars into strips about two and one-half inches wide, and of the required length, by a heavy cutting machine. These are carried into the adjoining forge room, where each piece is heated white, hammered by steam so that about twenty blows fall upon every part of its surface, and then thrown into a barrel of water. Afterward these pieces are again heated in a great coke fire, and each goes through a set of rolls, which reduce it to something like the desired shape of the weapon. The rough margins are trimmed off the piece of steel in another machine, and there is left a piece of dirty, dark-blue metal shaped like a sword, and ready for grinding. This is done on great stones, revolved and watered by machinery, the workmen having to be the most expert that can be obtained, as the whole fate of the sword is in their hands. It is afterward burnished on small wheels managed by boys from twelve to sixteen years old, and when it has been prepared to receive the fittings of the handles, is ready for testing, which has to be done with great care. Any fault in the work is charged to the workman responsible for it, and he has to make it good. It is said that any blade which will not chip a piece out of a stone without showing a nick on itself is rejected.

To Temper Steel on One Edge.

Red-hot lead is an excellent thing in which to heat a long plate of steel that requires softening or tempering on one edge. The steel need only to be heated at the part required, and there is little danger of the metal warping or springing. By giving sufficient time, thick portions may be heated equally with thin parts. The ends of wire springs that are to be bent or riveted may be softened for that purpose by this process, after the springs have been hardened or tempered.

Heating to a Cherry-Red—Points in Tempering.

What is a cherry-red heat? To answer this question I will describe how I do my work. My shop is well lighted by windows and I heat to a cherry-red in the shade on days when the light is good, but on cloudy days I don’t heat quite so high. I do not think that in hardening cast-steel it should be heated above a cherry-red in the shade. After hardening, temper thus: for razors, straw color: penknives, slightly bluish; screw taps and eyes, yellow; chipping chisels, brownish yellow; springs, dark purple; saws, dark blue.—By JOHN M. WRIGHT.

Brine for Tempering.

Brine for tempering is usually known as hardening liquid, or hardening compound. The tempering is done after the hardening, and is usually termed drawing the temper. If good crucible steel is used there is nothing better than rain or soft water to harden with, that is, for tools which are not so thin as to bend, spring, or break when hardening. When thin articles, such as knife or saw blades, are to be hardened, cold raw linseed oil is the best material or compound extant. The bath may be filled entirely with oil, or have a surface of oil say six inches, and six inches or more of oil underneath the water. Clear oil is best, because, when water is present the lower stratum of oil is likely to saponify or become soapy, and loses its cooling qualities.

When the steel is not uniformly hard or lacks the necessary amount of carbon for hardening properly, then re-agents called hardening compounds are used to produce the necessary hardness. Of these compounds there are many, some of value, and more of questionable character. I give a few good preparations. Avoid using hard water at all times.

Chloride of sodium (salt), 4 ounces; nitrite of soda (saltpetre), 1/2 ounce; alum pulverized, 1 dram; soft or rain water, 1 gallon; when thoroughly dissolved heat to cherry-red and cool off. This process hardens and tempers, or draws no temper.

Another preparation is: Saltpetre, 2 ounces; sal-ammonia, 2 ounces; pulverized alum, 2 ounces; salt, 11/2 pounds; soft water, 3 gallons. It is not necessary to draw with this mixture.

Another compound is: Corrosive sublimate, 1 ounce; salt, 8 ounces; soft water, 6 quarts. Corrosive sublimate is a subtle poison, so be careful with it.

While the above are of more or less value, the following will ever stand by you. It is in more general use than all the others put together:

Ferrocyanide of potassium, sometimes called prussiate of potash, 8 ounces, pulverized; 6 pounds of salt; 8 ounces of borax, pulverized; soft water, 10 gallons. The potash is poison, but when dissolved it becomes so well distributed in the water that its power as a poison becomes dissipated. For this mixture, as well as all others, use a wooden vessel, or a vitrified earthen vessel. The former is preferable. If prussiate of potash is not at hand, substitute 11/2 pounds of crude potash, or two gallons full-strength soap-makers’ lye, made by leaching hardwood ashes. In using this compound you will find that the salt and other ingredients are drawn to the surface edges of the vessel and form an incrustation on the outer upper section of the vessel, which you must remove and replace in the water. If in constant use replace the evaporated water with an equal amount pro rata of the ingredients. When much scale is deposited in the bottom of the vessel, remove the water to a clean receptacle, and clean the deposit from the vessel; replace the water drawn off and add sufficient water to replace the loss, and add ingredients pro rata. This preparation is in use by all file makers, and in it are hardened the smallest files extant. With care (keeping covered when not in use), a bath of this preparation may be kept with proper additions for years. I know of one bath of this kind which (by the necessary additions) has been in constant use thirty years. It is a tank holding about eighty gallons. Its owner would not dispose of it for $1,000. He makes the best files produced in America. For tools of any kind which are not liable to spring in hardening I do not know of a better ordinary process.—By IRON DOCTOR.

A Bath for Hardening Steel.

I have a hardening bath that is good and cheap. It is made as follows: Potassium cyanide, 2 ounces; ammonia carbon, 1 ounce; soda bicarbon, 1 ounce; aqua pura (water), 1 bbl; sodium chloride (salt), 15 lbs.

I use a coal oil barrel. The plow lay should be of an even cherry-red all over. Hold the lay with tongs at the heel, put it into the water point first, but not too fast or it will spring, and keep the lay under water until it is cold.—By E. W. S.

The Lead Bath for Tempering.

Among the many secrets of tempering is the employment of the lead bath, which is simply a quantity of molten lead, contained in a suitable receptacle and kept hot over a fire. The uses of this bath are many. For instance, if it be desired to heat an article that is thick in one portion and thin in another, every mechanic knows how difficult it is to heat the thick portion without overheating the thin part. If the lead bath be made and kept at a red heat, no matter how thick the article may be, provided sufficient time be given, both the thick and thin parts will be evenly and equally heated, and at the same time get no hotter than the bath in which they are immersed.

For heating thin cutting blades, springs, surgical instruments, softening the tangs of tools, etc., this bath is unequaled.

If a portion of an article be required to be left soft, as the end of a spring that is to be bent or riveted, the entire spring may be tempered, and the end to be soft may be safely drawn in the lead bath to the lowest point that steel can be annealed without disturbing in the least the temper of the spring not plunged in the bath. Springs, or articles made of spring brass, may be treated in the same manner. A great advantage in the use of the lead bath is that there is no risk of breakage by the shrinkage of the metal at the water line, as is often the case when tempered by the method of heating and chilling in cold water.

As lead slowly oxidizes at a red heat, two methods may be used to prevent it. One is to cover the surface of the lead with a layer of fine charcoal or even common wood ashes. Another, and a better plan, is to float on the top of the lead a thin iron plate, fitting the vessel in which the lead is contained, but having a hole in the center or in one side, as most convenient, and large enough to readily admit of receiving the articles to be tempered or softened.—By W. H.

Hardening Small Tools.

It is said that the engravers and watchmakers of Germany harden their tools in sealing wax. The tool is heated to whiteness and plunged into the wax, withdrawn after an instant and plunged in again, the process being repeated until the steel is too cold to enter the wax. The steel is said to become, after this process, almost as hard as the diamond, and when touched with a little oil or turpentine the tools are excellent for engraving, and also for piercing the hardest metals.

Hardening in Oil vs. Hardening in Water.

I have made and tempered cutters for straight and irregular molders, sash tools, etc. If tempered in oil they will hold their edges better, cut smoother and longer than if tempered in water. In hardening, the oil cleaves to the steel, which is in consequence longer cooling. The water seems to separate, leaving air spaces between the steel and the water. Water cools quicker and hardens harder than oil and consequently steel hardened in oil must be left at a higher color than when hardened in water. A good deal depends on the heating of the steel to get a good temper. While water injures the quality of the steel, oil improves it.—By D. D.

Tempering Plow Points.

If the steel is good, nothing will temper a plow point better than good clear water, with perhaps a little salt in it. Harden at as low a heat as the steel will bear, and do not draw the temper for blunt tools for cutting stone. Heat your plow points in the same manner. The great trouble with plow points is in the poor quality of the steel. You may make the plow points better by case-hardening, which every blacksmith knows how to do, and harden at a low heat without drawing the temper. —Scientific American.

Tempering Blacksmiths’ Tools.

Some blacksmiths will, perhaps, be glad to know that by sifting prussiate of potash on red-hot iron and cooling it immediately, a temper is obtained hard enough to make a great many of the anvil tools used by smiths.—By I. C.

Softening Chilled Castings.

For softening chilled castings my plan is as follows: Heat the metal you wish to drill in the fire to a little above a cherry-red. Then remove it from the fire and immediately place a lump of brimstone (sulphur) on the part to be drilled. You can keep the metal on the fire so as to retain heat and continue to throw sulphur on it until it will be as easy to drill as pot metal is. —By F. B.

To Harden Cast-Iron.

Heat the iron to a cherry-red, then sprinkle on it cyanide of potassium (a deadly poison), and heat it to a little above red, then dip. The end of a rod that had been treated in this way could not be cut with a file. Upon breaking off a piece about half an inch long, it was found that the hardening had penetrated to the interior, upon which the file made no more impression than upon the surface. The cyanide may be used to case-harden wrought-iron.—Scientific American.

Brass Wire—How Should it be Tempered for Springs?

Brass wire cannot be tempered, if, by tempering, is meant the method of tempering steel springs. The only method to make a brass spring is by compressing the brass by means of rolls, or by hammering. The latter method will be the one that will probably be used. If the springs are to be flat, hammer them out to shape in thickness from soft wire, or sheet brass, somewhat thicker than the finished spring is to be. If the brass shows a tendency to crack in hammering it must be annealed, which can be done by heating to a light red and plunging into water. In hammering use a light hammer, and don’t spare the blows.—By H.

To Harden Steel Cultivator Shovels.

Shovel blades will harden in good soft water, with a little sal ammoniac in it, say one pound to ten gallons of water, if they are not put in too hot. Steel will harden best at a given heat, and practice alone will teach what that heat is. Clean the blades well, or, better still, polish them; then cover them with a paste made of salt and shorts, or flour and heat them very slowly.—By E. J. C.