PART II

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MATERIALS EMPLOYED IN HOROLOGY.

IRON.

=54.= Iron is an elementary body, that is to say it cannot be decomposed. It is the most tenacious of the metals, having a breaking strain of about 75 kilo. per sq. mm. (or 106,000 pounds per sq. inch) of section. Two pieces can be perfectly welded together when raised to a white heat.

In the smaller horological appliances, the metal is not employed except after conversion into steel. In common clocks it is used from motives of economy, for forming pins, screws, etc. In turret clocks, however, considerable use is made of it, many of the parts after they are formed being cemented, that is to say, having their surface rendered hard in a manner subsequently indicated (=65=).

Such a mode of manufacture is particularly applicable to pieces that are subject to a constant succession of impacts; their hardened, steelified surface resists wear, while the iron core affords security against rupture.

It is important to carefully distinguish the cases in which iron is preferable from those in which its substitution for steel serves merely to augment the profits of the manufacturer.

The fracture of a good piece of iron is characterized by long twisted fibres of a brilliant white color.

If heated frequently or carelessly, the quality of the metal is impaired—it ceases to be fibrous and looses its tenacity: in this condition it is said to be _burnt_.

It is better to work with a charcoal or gas fire, as coal acts more rapidly in rendering the metal brittle. Cold hammering, or “hammer-hardening,” also makes it brittle and diminishes its tenacity, but this is again restored by a suitable annealing.

Iron dissolves slowly in dilute nitric acid; if not diluted, this acid rapidly oxidizes it. Dilute sulphuric acid dissolves the metal easily, but if concentrated, it has no action in the cold, whereas, on heating to ebullition, the iron is dissolved with evolution of sulphurous acid gas. It is also dissolved by hydrochloric acid, or aqua regia.

Iron is less magnetic than steel, especially hardened steel, which, owing to its great coercive force, is magnetized with greater difficulty, but retains its magnetism for a longer period. Indeed, _soft iron_, if properly prepared, can be magnetized and demagnetized instantaneously.

Some workmen can distinguish iron from steel by the musical note emitted on striking. A more certain method, however, consists in using dilute nitric, or sulphuric acid. If the surface remains unaltered, or nearly so, when touched with a drop of either acid, the metal is iron, but, in the case of steel, a black mark will be left, owing to the liberation of carbon.

=55.= =To Remove Rust.= The usual mode is to rub the object with a piece of oiled rag, or emery paper. It appears that more rapid and more satisfactory results are secured by using very pure petroleum, and wiping with a hempen or woolen rag.

=56.= =To Prevent Rust.= Dip iron or steel articles in a mixture of equal parts of carbolic acid and olive oil, rubbing the surface with a rag. Others rub the metal with a mercurial ointment, leaving a thin layer over the entire surface. It is stated that, if iron be dipped in a solution of carbonate of potash or soda in water, the surface will be protected against rust for a long time, and objects can be protected for any period by burying in quicklime. Rubbing the surface with plumbago has a similar effect, and Barff has pointed out that, by exposing iron to the action of steam, heated above the boiling point of water, a coating of magnetic oxide of iron is formed, which is equally serviceable.

=57.= =To restore iron and steel that has been burnt, or badly forged.= When iron is burnt, or carelessly forged, it becomes crystalline and brittle; in order to restore it to its original condition, a fresh and very careful forging is generally needed. This can be avoided by having recourse to the following method, suggested by Caron: it consists in treating the metal somewhat after the manner adopted in hardening steel.

He experimented with a bar of good iron, which was easily bent when cold, without breaking or showing any cracks. It was then burnt and became brittle when cold, the fractured surface showing brilliant shining facets.

Prepare a boiling saturated solution of sea-salt, heat the piece of iron to a bright redness, and plunge it into the bath until it is of the same temperature (about 110° C. or 230° F.) After undergoing this operation, it is found that the metal can be easily doubled in the cold, exactly as it did before being burnt.

Perret states that steel which has been deteriorated by frequent hardening can be restored as follows: Heat it short of dull redness and quench in melted tallow, repeating the operation, if necessary, when the steel may be again hardened in the ordinary manner, and will be nearly, if not quite, restored to its original condition.

CAST IRON.

=58.= This is only used in the manufacture of tools and large clocks; the employment of cast iron wheels in the striking train of such clocks has materially reduced their price.

Like steel, it is a compound body, consisting mainly of iron and carbon. Cast iron, however, differs from steel in the quantity of carbon present, for, whereas its proportion in cast iron varies from 2 per cent. upwards, there is never, in steel, an amount exceeding 1.5 per cent., and even .5 per cent. renders an iron hard, converting it into “mild” steel.

Cheapness is not the only argument in favor of the use of cast iron. In virtue of its molecular structure, this material offers a considerable resistance to a crushing strain, so that the teeth of wheels, made of carefully selected cast iron, will work for a long time without sensible wear; moreover, the founder’s art has made such important advances that there is no difficulty in casting, to a constant pattern, a wheel, together with the pinion that it carries, and any other projections, etc., that may be required; this economizes labor to a very great extent.

The use of cast iron in the construction of certain classes of wheels, and parts of tools, presents advantages which we cannot afford to ignore; but it must be carefully observed that this material is not suitable in cases where great accuracy in the acting parts is required, as it cannot, like brass and steel, be conveniently worked by the turning tool or file. In recent years, however, this difficulty has been overcome by the introduction of what are termed “malleable castings,” produced as follows:

=59.= =Malleable Castings.= The object is first made of ordinary cast iron, and the invention consists in rendering this malleable by the removal of the carbon that has served the very important purpose of rendering the metal fusible. In large cast iron pots, the castings are laid with alternating layers of powdered red hæmatite, and the whole is kept at a temperature of about 900° C. (1,650° F.), or cherry-red heat, for 72 hours. On cooling, the castings are found to consist of nearly pure iron, and to be perfectly malleable, and, therefore, workable.

STEEL.

=60.= The treatment of steel involves some of the most prolonged and delicate operations in the entire range of horology. If the metal is badly selected and prepared, the working of it will be laborious, difficult and unsatisfactory; the resulting object will be distorted in the hardening, and will not harden uniformly; in short, it will occasion much toil and loss of time, with very little success.

Let the young watchmaker accustom himself from the first to study the steel that he uses, so that he may be thoroughly cognizant of both its advantages and defects; he will, in the practice of his art, be amply repaid for the brief time spent in making such an examination.

=61.= Steel is not an elementary body; it is usually regarded as a carbide of iron, that is to say a combination of carbon and iron. Analysis, however, proves other substances to be usually present in almost infinitesimal quantities; their remarkable influence on the physical properties of the metal has not yet been fully investigated, but much attention is being devoted to them at the present day.

The varieties of steel are very great. What are known as _puddled_ and _natural_ steel are obtained by acting directly on cast iron. _Cementation_ is a very old method of converting bars of malleable or pure iron into steel by enclosing them in charcoal and heating the whole for several days, until the carbon has worked itself into the center of the bars in such quantity as to covert the iron into steel.

The steel obtained by the above method is very heterogeneous; in other words, the composition is not uniform throughout a given block or bar. One part is highly carbonized, whereas another part, especially towards the center, will not be sufficiently so. The _grain_, although very fine in one part, will be more coarse in another; hard particles of pure cast iron, termed “pins,” are to be met with that resist the action of the graver or the file and give rise to cracks in the hardening, hammering, etc., and portions or sometimes even entire layers that have taken up no carbon whatever. The differences in the density, hardness, malleability, etc., that can be shown to exist at different points in the same bar arise from this cause.

Such faults can in part be corrected by _shearing_, an operation which consists in binding together a number of bars in a bundle, raising them to a red heat and beating them with sledge or steam hammers so as to weld them into one. The bar thus obtained is again heated, folded several times on itself, again hammered, rolled, etc., when it is termed _shear steel_. If these operations are performed carefully and without a too great heat, the quality of the steel is much improved; it is more homogeneous and can be worked with greater facility.

=62.= The discovery of the earliest method of producing _cast_ steel, thoroughly homogeneous, was made by a watchmaker, B. Huntsman, of York, and metal produced by his method is very highly prized at the present day. Many other methods have been since introduced, amongst which may be mention the Bessemer and the Siemens-Martin processes, and steel is now produced from iron of very varying quality, so that the mark _cast steel_ is now far from being a guarantee of quality. The fusion of shear or cement steel will only secure a marked superiority in its quality under two principal conditions: (1) The metal must be carefully selected, since certain qualities do not intermingle thoroughly. (2) Very great care and skill must be devoted to all the operations, the successive heatings, forging, rolling, etc.

In short, in the case of steel it is exceptionally true that we must never accept the metal merely on its own recommendation. Whatever maker’s mark is selected, the results obtained will never be satisfactory unless the degree of hardness, the elasticity, cohesive force, etc., are such as will suit the metal to the special purpose to which it is to be applied as well as to the working it will have to undergo. _Experiment can alone make us fully cognizant of the qualities of a steel._

GENERAL OBSERVATIONS.

=63.= All steels, if of good quality to begin with, will deteriorate if subjected too often or too long (according to the character of the metal) to the action of either the fire or the hammer. They will become brittle and incapable of hardening, in the end even reverting to the condition of iron.

The quality of steel becomes worse as the number of flaws, blackish filaments, more or less carbonaceous veins, and occasional particles of pure iron in its substance are greater; as its surface is _cindery_, that is to say spotted with minute black marks which become more prominent after polishing, etc.; as its fracture presents an uneven grain, etc.

Such a metal is found to vary considerably as regards hardness, elasticity, etc.; not being uniformly affected in the hardening, it becomes difficult to work with the file and almost impossible to form into a perfect cylinder in the lathe.

Other conditions being equal, these faults are characteristic of natural steel rather than of the two other varieties. At the same time, if well sheared, it becomes very elastic, and has the great advantages of not being deteriorated under the hammer and of being less ready than the other varieties to be converted into iron.

Rolling, wire-drawing and hammering occasion a molecular re-arrangement; it is necessary, therefore, to anneal the metal from time to time, as otherwise it becomes brittle or cracks.

There is a certain temperature, corresponding to each variety of steel, which cannot be exceeded without the metal being injuriously affected; this temperature must, then, be previously determined.

The grain of a piece of steel that has been superheated or _burnt_ is characterized by brilliant diamond-like particles; the mass loses its beautiful color, and resembles iron more or less according to the degree of heat applied.

Some few workmen are enabled, by long experience and a very delicate touch, to judge approximately of the quality of a steel from its weight, feel, and resonance. Metal that is of a good quality, homogeneous, and very dense, they term _full_.

SPECIAL OBSERVATIONS.

=64.= =Natural Steel.= In the case of natural steels of low quality, the fracture is usually characterized by uneven grains, a somewhat fibrous nature and a bluish tint. The grain becomes finer and more even and the surface presents more and more the appearance of a piece of coke, as the quality of metal improves. In addition to these distinctive features a natural steel of high quality can be distinguished by the fact of its being more thoroughly hardened and less liable to break when hard.

In hardening it must be raised to a higher temperature than cement steel; in other words, steel of a low quality must be heated somewhat above bright redness, while the better qualities should be heated to an orange-red, or nearly so (=77=).

=65.= =Cement Steel.= The cement steel ordinarily met with has a lamellar fracture, the lamellæ varying in form and color from the center towards the circumference. The grain is usually finer and more uniform than that of natural steel, there is seldom any appearance of fibres, veins, or flaws. The color of the fracture is greyish, tending towards blue in the ordinary qualities.

The better qualities are marked by a closer grain, a more uniform, dull, greyish-white color, exhibiting neither streaks or black spots after hardening, and by the further fact that hardening can be effected at a lower temperature. If of the very best quality, it should not require heating beyond a clear cherry-red; often even a still less degree of heat will suffice.

=66.= =Cast Steel.= Cast steel is the most homogeneous, full, and beautiful of the three classes. Several varieties exist. The fracture of cast steel, as compared with others, is smooth, compact, and of a white-grey color, resembling coke. The grain is fine and very even. The metal must be hardened at a temperature much lower than can be safely applied to other classes of steel, since it is rapidly deteriorated by heat.

Cast steel is more fusible than ordinary steel, and will fracture with ease under the hammer when heated to a blue tint, so that great care is essential in hammering it.

The metal should never be heated beyond a dull or cherry-red heat, lest it be _burnt_.

The tenacity will be increased by forging at a low temperature or even by cold hammering.

The fineness in grain, together with its high density, afford an indication that the metal can be rendered very uniformly hard; that very fine cutting edges and the most minute rods can be made of it; and that, after hardening, it can be highly and uniformly polished; in other words, that it does not exhibit spots or streaks differing in color from the mass, as is always the case with natural and cement steels. For most horological purposes (such as making pinions, staffs, pivots, etc.) cast steel is preferable. It is the only kind that can with certainty be highly polished, turned perfectly round, and that does not get distorted in the smoothing. Moreover, when wear does occur it exhibits less irregularity.

Highly-carbonized shear steel exhibits a fine, close grain that would make it easily mistaken for cast steel. They can be best distinguished by the application of dilute sulphuric acid. The side of the bar when acted on by this means exhibits lines that indicate the junctions of the several layers constituting shear steel.

DETERMINATION OF THE QUALITIES OF STEEL.

=67.= It is unnecessary to observe that as we are writing mainly for the use of practical watch and clockmakers, we shall make no reference to those elaborate systems of testing that form a remarkable feature of the engineering of the present day, but shall confine ourselves to the tests which workmen can apply for themselves.

When the grain is fine, close and homogeneous, the fracture in even curved lines and the surface of a uniform grey aspect, the metal is considered to be of good quality. It is, nevertheless, unsafe to rely too much on such indications, for a steel that has been hammered until cold will exhibit a fine close grain, whereas the grain of the same metal will be coarse and open if it was still red hot when the hammering or rolling was concluded. The grain of hardened steel, moreover, depends on the degree of heat to which it has been subjected.

When of equal quality, even if from the same maker, the grain will be finer in bars of small dimensions than in those that are larger.

Cast steel even, especially in large pieces, is not always perfectly homogeneous, as can be easily perceived on applying the file, or still better, in the lathe; an object can with difficulty be turned perfectly round, and loses its shape in the smoothing. _As a general rule it is impossible to form a reliable opinion on a specimen of steel until after it has been worked, filed, turned, and tested according to the particular use to which it is to be applied; for a steel that is excellent for making, say, a spring or a cutter, may be quite unsuitable and give most unsatisfactory results if used for making staffs or fine pivots, or the converse may be equally true._

As a preliminary test, break a piece of the metal; after having examined the fracture, form a cutting edge, harden to what seems to be a convenient degree, then sharpen and employ for cutting small pieces of iron. If the edge is in no way damaged by the iron, this may be taken as a good indication that the metal possesses body and tenacity, and that it can be hardened as much as is required for such purposes.

The following are methods of obtaining more complete information as to the homogeneity, the character of grain, the degree of hardness a given sample can attain, as well as its malleability, body, elasticity, etc.

=68.= =Homogeneity.= Place drops of dilute sulphuric acid equidistant along the surface of a bar. If the metal is homogeneous all the drops will impart the same color.

Cold hammer or hammer-harden, and then fire-harden part of the bar. Break off the extremity in order to study the fracture; if the result of this examination is satisfactory, polish the hardened end carefully, and with the aid of a glass again examine into the homogeneity of the metal. The polish will be the better and more uniform according as the steel is more homogeneous.

=69.= =Grain, hardness and temperature of hardening.= All varieties of steel do not harden to the same degree, and each requires to be heated to its own particular temperature for hardening; moreover, the character of the metal, its color, and the size of its grains vary according to the degree of heat to which it is subjected. It would be difficult to draw any exact conclusions as to the character of grain and the hardness without the following practical method, which we owe to Reaumur:

At a temperature not exceeding a dull redness, forge a piece of the steel to be tested into the form of a razor-blade, that is to say, leaving it thick on one edge and thin on the other, in the direction of its length. Then heat the blade, holding it by one end, and when the other end has reached a bright red heat, plunge the whole into water. Part of the steel will then be hard hardened. Along the entire length of the thinner edge carefully break off the metal with a hammer or otherwise, and examine the character of grain at different points of the exposed thicker edge thus left.

As the form, color, etc., of the grain depend on the degree of heat to which each portion was subjected, it follows that we shall observe four types of grains: (1) Large, white, sparkling grains; (2) Grains that are medium sized and intermixed, some being white and sparkling, others white and dull; (3) Fine dull grains; and (4) Grains that are medium sized, but dull and ill-defined.

According as the third class of grains is observed to be more numerous than the second class, so is the fineness of the steel greater, and conversely.

This method of testing possesses, moreover, the advantage that the workman can experiment on his blade of steel with a view to determine the temperature best suited for hardening.

Grain No. 1 corresponds to a white-red heat for hardening.

Grain No. 2 corresponds to an orange-red heat for hardening.

Grain No. 3 corresponds to some shade of cherry-red heat for hardening.

Grain No. 4 corresponds to a dull red heat for hardening.

As there is some difficulty in remembering the exact points at which these several temperatures are reached we will complete this account of the mode of testing by the following:

=70.= On a thick plate of metal, maintained at an orange-red heat, place three fragments of the steel under examination, previously marking them, so as to observe the order in which they are immersed in water; and have three vessels of water standing near. As soon as one of the pieces reaches a dull cherry-red heat, allow it to slide into one of the vessels; heat the second to a medium cherry, and the third to a bright cherry-red, introducing them in succession into the water-vessels. If these pieces be examined as to the resistance they offer to breaking, and the fracture of each be compared with the fracture at different points of the razor-blade, the file being used to test hardness, we shall have sufficient evidence as to the most suitable temperature for the hardening of this particular variety of steel.

=71.= =Body.= A steel that possesses _body_ is not brittle. This quality may be tested in the following manner: Several bars of different kinds of steel, of equal dimensions and hardened as uniformly as possible, are bent until the breaking point is reached. If all the conditions of the trial are identical, those bars that stand the greatest angular deflection without breaking have the most body.

Steel that possesses body does not break as easily as that which is wanting in body. Its fracture will be, as it were, bevelled off like the mouth-piece of a whistle. If soft and fibrous, it will be characterized by parts being torn asunder.

=72.= =Elasticity.= The elasticity may be tested in a similar manner. It is proportional to the curvature or to the weight that a rod or blade of the metal under examination can support without failing to return to its initial position as soon as the weight or obstacle is removed. A sample of steel that is distorted by a weight that another specimen resists, is evidently inferior in elasticity.

=73.= =Malleability, tenacity, ductility.= A cold hammering, if carefully managed, will suffice to indicate the limits between which steel will support frequently repeated percussion, without breaking, cracking or flying.

Forge a piece, introducing it a number of times into the fire in order to ascertain whether it loses its distinctive characteristics rapidly, and whether it can be successfully forged.

It is more difficult to forge, according as it is harder and more “steely.”

The degree of malleability is indicated by the manner in which it supports hammering and rolling, and by the smallness of the dimensions to which it can be brought by such operations.

Passing the metal through a draw-plate with smooth holes, or tapping it in a screw-plate will give useful indications as to degree of ductility and tenacity.

A metal is said to be _malleable_ when it can be easily spread out under the hammer or in the laminating rolls. It is called _ductile_ when it can be reduced to very thin wire by passing through the draw-plate.

It would seem that these two properties, ductility and malleability, should always exist together, to the same degree, in any given metal, but such is not the case. Iron can be drawn into very fine wire, but cannot be reduced to sheets of relatively equal thinness; tin and lead give leaves of extreme thinness, but cannot be drawn out into very fine wires; gold and silver are both very malleable and ductile, and they rank highest as regards the possession of these properties.

Steel is more fusible and malleable than iron, but less ductile.

=74.= _Observations._ Formerly the makers of cylinder escapements preferred forged steel, and their cylinders often cracked after the hardening: modern makers employ drawn steel, and it is much preferable. At the same time they do not appear to recognize the principal reason for the difference in the two varieties of steel. It seems to us to be as follows: forged steel is malleable; drawn steel, which has passed well through the draw-plate, is ductile, and, therefore, tenacious. But tenacity in a metal is nothing else than an exceptional resistance, opposed by its particles to a fracture or separation; it follows, then that drawn steel will crack with less facility than the other.

PREPARATIONS OF STEEL.

=75.= When a variety of steel has been selected that possesses the requisite properties: that is to say, fibre and elasticity for springs; body and tenacity for circular cutters, gravers, etc., it must be prepared; in other words, it must be made so that it can be worked with ease, for steel that is badly prepared will resist both the file, the graver and the drill. It can never be turned perfectly round, and will harden unevenly.

=76.= =To anneal steel.= The commonest, and at the same time best, method consists in heating the metal to a dull, red heat, burying it in hot ashes and allowing it to cool slowly.

Steel raised to a red heat in contact with air loses a portion of its carbon, so that it is better to place the metal in a vessel of burnt clay; this is introduced into a fire which must not be too bright at first, and when the vessel has attained a red heat the fire is checked and left until the whole is quite cold.

In order to soften steel by annealing with a view to work it, engineers entirely cover the metal with dry powdered wood charcoal or dry iron filings or turnings, in a cast iron box or pot, or in a crucible, shutting up all the openings so as to protect it from the direct

## action of the fire and from the air. The vessel is then put in a dull

fire, the heat being gradually raised until the whole has acquired the requisite temperature, which is known by observing the color (see the following table); this degree of heat is maintained for about ten minutes and the fire quenched, after which it must be allowed to gradually die out. Frequently the cooling is not complete for a day or two, and even more when the crucible is of large dimensions.

The metal will become softer, according as the cooling is more slowly effected. It is generally heated to 800° or 900° C. (1500° or 1600° F.), a cherry-red heat. When the steel is associated with brass, as in the case of a compensation balance, it is not safe to exceed 600° C. (1000° F.)

=77.= It will be useful here to give the following table, compiled by Pouillet, of the temperature, as indicated by the air-thermometer, corresponding to various colors of a heated body:

Incipient red heat corresponds to 525° C. ( 980° F.) Dull red ” ” ” 700° C. (1280° F.) Incipient cherry-red ” ” 800° C. (1470° F.) Cherry-red ” ” 900° C. (1650° F.) Clear cherry-red ” ” 1000° C. (1830° F.) Deep orange ” ” 1100° C. (2010° F.) Clear orange ” ” 1200° C. (2190° F.) White ” ” 1300° C. (2370° F.) Bright white ” ” 1400° C. (2550° F.) Dazzling white ” 1500-1600° C. (2730-2910° F.)

=78.= _Annealing or softening in water._ Instead of allowing a piece of steel to cool slowly, it may be thrown into water when heated to a temperature just below that at which it would harden. In this case the metal will not harden, but, on the contrary, become very soft. A single operation suffices for certain varieties of steel, but with others it must be repeated.

The only difficulty consists in fixing upon the precise moment at which the metal has the requisite tint (a purplish yellow or dull red), and this is more especially felt when dealing with small pieces; experience can alone guide the workman in this matter.

A skilful workman recommends the employment of water containing one-fifth of its weight of gum arabic. He also recommends that the metal be wiped over with an oiled rag, then held in the fire, and, as soon as the oil is converted into a thick smoke, and is on the point of igniting, to immerse in water.

=79.= =Hammering steel.= Watchmakers who are called upon to manipulate exceedingly small pieces of steel, can somewhat increase the body and homogeneity of the metal by a cold hammering. After annealing, the object is hammered with light, uniform blows, again annealed, and the same operation is repeated one or more times, according to the degree of malleability already acquired by the metal. Steel thus prepared has more body; the particles composing it are more closely pressed together; it files and turns well, can be heated more evenly, and is not distorted or only very slightly in hardening, providing the requisite precautions are taken.

=80.= _The hammer and anvil._ It is important that in these operations the surfaces of the hammer and anvil employed be perfectly smooth and even polished. If they are rough or cracked, if they are uneven or have a grained surface, a flaw will be produced in the body of the steel or a crack on its surface.

=81.= =To clean rough steel.= The black coating known as “scale,” which covers the surface of the metal after it has been in the fire, will rapidly spoil gravers and files, and, in addition to this, it leaves behind in them excessively hard particles that will become imbedded in the steel itself after a clean surface has been exposed. It is then essential, in order to ensure good and rapid workmanship, to previously remove this crust from the surface.

This can be done in two ways: by using a rapidly-revolving grindstone, which instantaneously removes the oxide, at the same time smoothing the surface of the steel; or by leaving it for a sufficient length of time in dilute acid, by which the superficial oxide is dissolved.

Sulphuric acid is usually preferred; in addition to the cleaning, it is said to produce an effect somewhat similar to annealing. On withdrawal from the acid, the steel must be thoroughly washed with water and wiped dry with care.

=82.= =Ordinary mode of preparing steel.= When the metal has been annealed by one of the methods indicated above, its preparation is completed by “pickling” in acid, after which it is hammered cold between an anvil and hammer (=79=, =80=). When the metal has been worked, it is heated to a bluish tint, and after cooling slowly is ready for the hardening.

=83.= _M. Covillot’s mode._ This author adopts a method whereby he obtains steel that is very soft to work and perfectly free from hard grains or “pins” of cast iron, which are so often to be met with in steel, causing it to crack in consequence of their inability to spread under the hammer.

Take some garlic, the younger the better, mix it with sufficient good walnut-oil to cover the garlic and form into a paste; then place it in an earthenware pot on the fire. When beginning to boil, heat the steel to dull redness and plunge it into the boiling paste. Withdraw it with a quantity of oil and garlic adhering; again heat to redness and plunge into the paste. This operation may be repeated two or three times. Then heat the steel, while inclosed in an iron tube or box placed on the fire, and allow the whole to cool. Finally, the steel may be finished by setting it to _cook_ (if we may use such an expression) for ten or twelve hours in the composition of garlic and nut-oil.

The last operation may be performed by setting the boiling solution over an oil-lamp, after depressing the wick in such a manner that the paste may be kept just simmering.

M. Covillot employed the same mixture for hardening the objects; but then, of course, it must be cold.

HARDENING.

=84.= It is well known that by the operation of hardening, which consists in heating a piece of steel to a red heat and immediately chilling it, the hardness is very materially increased.

Hardening increases the dimensions of the object. A steel collar adjusted to fit a cylinder will slide on more easily after hardening.

Rolled steel is more liable to be distorted in the hardening than metal which has been forged or hammer-hardened. As a general rule, when steel—especially cast steel—has been carefully annealed, cold-hammered and, after working, heated to a blue temper and slowly cooled, it will not be distorted in the hardening, providing the heating is skillfully conducted, and if, at the moment of introducing the object vertically into the bath, the heat is evenly distributed throughout. Some practical men affirm that the mere presence of an oily layer on the surface of the water will check the tendency to distortion.

A workman frequently pretends that he has some exceptionally good solution for hardening, of which a great mystery is often made; but it is very generally admitted by those who are well-informed that these so-called secrets are a delusion and in no sense superior to pure water. There is a certain amount of truth on both sides, and the former class are somewhat justified by experiments with the various solutions enumerated below. We may, however, lay down the three following conditions as essential to the successful conduct of the operation of hardening: (1) _The steel must previously be carefully prepared and worked_; metal that has been skillfully hammered cold or below a red heat, for instance, will harden better than when not so treated; but if hammered too much or carelessly, it will crack; (2) _The method of heating_ should be such that the heat is evenly distributed throughout the object; if, on immersion, its temperature is not uniform, the degree of hardness will vary; (3) _The skill of the workman_ must enable him to detect the exact degree of heat the variety of steel can withstand, and this must on no account be exceeded, for in that case the steel will lose tenacity, will be more or less _burnt_, &c. In the case of irregular shaped articles, considerable skill is often needed to ensure that the several parts of the mass shall be cooled at, approximately, the same rate.

=85.= =Methods of hardening.= The baths used for hardening may be classed under three heads: _Tough_, _Hard_, and _Glass-hard_. It must be understood, however, that these classes may be made to merge more or less into one another, by varying the degree of temper.

=85a.= The following receipts are drawn from various sources, and the reader is recommended to select the one which he finds on trial to be best adapted to his requirements, for, as Prof. Akerman has pointed out, there are very many conditions exceedingly difficult of calculation that influence hardening, and hence it follows that a workman accustomed to hardening often considers that only one method, which he has been in the habit of employing, can be used for a certain purpose, while another equally skillful workman can only attain the same result by a method essentially different.

I. _Tough._ Tallow; tepid water; oil; resin; sealing-wax; lead; beeswax; a solution of 3 to 4 parts (by weight) of gum arabic in 100 parts of water; 1 part of soft soap in 100 parts of water; cold water with a layer of oil over it, the thickness of which varies with the degree of hardness required; 10 parts mutton suet, 5 parts resin, 2 parts sal-ammoniac, and 35 parts olive oil.

II. _Hard._ Cold water; water containing various salts, such as sal-ammoniac and sea-salt; a solution of 5 parts sea-salt and 1 part sal-ammoniac in 20 parts of water; 4 parts sulphuric acid, 50 parts sea-salt, 10 parts alcohol, and 1,000 parts water (all by weight); 4 parts sulphuric acid, 1 part nitric acid, 1 part pyroligneous acid in 1,000 parts water (to be used very cold).

III. _Glass-hard._—Mercury; nitric acid; opium; any cyanide.

=86.= As a rule it is well to employ tallow for the hardening of small objects in which hardness without brittleness is needed. Oil renders the surface harder than the interior, and soapy water has the same effect. Saline solutions generally give great hardness. Very minute drills may be hardened by simply whisking them about in the air after heating the blade to redness, and small objects may be hardened by pressing between two cold surfaces, as those of the hammer and anvil.

If hardened in nitric acid, opium, or mercury, the hardness of steel is so great that it will easily cut glass. But such steel is brittle and all the more delicate according as the precise temperature necessary (which is not very high) has been exceeded. For it must always be borne in mind that steel which has been heated too highly has deteriorated in quality and will remain brittle.

=87.= =Precautions to be observed in hardening.= In the case of delicate pieces it is necessary to avoid the use of the blow-pipe, as the current of air causes the surface to scale, and, as is well known, the metal being unevenly heated will be distorted in the hardening, and will not be uniformly hardened.

It is better to enclose the article between two pieces of ignited charcoal, or in a metal tube, or to bring it in contact with a sufficiently hot piece of metal, etc. An excellent plan is to heat the article in a bath of hot lead, or of lead and tin in proportions dependent on the temperature required. The heating is thus exceedingly uniform, and, if operating in a dark room, the temperature can be accurately judged.

When it is required to harden an object without discoloring the surface or destroying the polish, it may be placed in a tube, and completely surrounded with powdered wood charcoal, or, preferably, animal charcoal. The whole after being heated is plunged in water without the steel being in any way exposed to the air. The powder must be heaped up as a precaution against access of air. On being taken from the water, the steel is at once placed in alcohol, and if at all dull it will generally be only necessary to rub the surface with a little rouge.

It is essential that the animal charcoal be previously heated in order to expel moisture, as otherwise it would adhere to the surface and produce marks and even irregularity in the hardness.

As a rule the object must be immersed in the cooling liquid vertically in the direction of its greatest length, and if of unequal thickness, the stout portion should touch the surface first, so that the metal may cool more uniformly. In hardening large masses of steel, various devices are resorted to in order to insure uniformity in the cooling, but space prevents us from entering more fully into this interesting question.

The vessel must be of such a depth that the object will not reach the bottom until quite cold. It is liable to distortion if introduced sideways, or if the vessel is too shallow.

The method described above for protecting the surface from the action of the fire should be adopted when hardening delicate or complicated articles; but in the case of drills, for instance, a simple coating of one of the following preparations is sufficient.

When an object is hardened in a saline solution, it is well to cover it with a paste composed of water, salt and flour (some use yeast and salt for this purpose), or a thin clay. This precaution prevents any blistering or oxidation of the surface. If it be desired to avoid oxidation, and, at the same time, to restore to the steel the carbon it has lost owing to the action of the fire, it must be rolled, while still wet, in another paste, containing powdered horn or leather, or some such calcined animal matter. Delicate parts can also be protected by a layer of beeswax and olive oil made hot.

In hardening small drills, very good results are obtained by enclosing the blade in a pellet formed of prussiate of potash, lard and Castile soap, and cooling in beeswax, or the surface may be protected by a layer of soft soap.

Steel as forged, that is with the thin scale on, is less liable to break in hardening than if previously brightened, for the scale causes it to cook, and, therefore, contract more slowly. At the same time it should be borne in mind that when the surface is bright the hardness will be somewhat greater.

It will be well to warn the beginner that, if an object is not entirely immersed in the cooling liquid, it should never be held still, but rapidly moved up and down, as otherwise there is a liability to crack at that part which was level with the surface.

As a watchmaker only uses steels of the best quality, he should, in hardening never exceed a cherry-red heat, and cherry-red comprises three distinct tints (=77=); incipient cherry-red, cherry-red, and clear cherry-red. The second of these should not be exceeded in hardening cast steel, and the third should be taken as an extreme limit in the case of shear steel.

Ice-cold water should never be employed, but the extreme chill should be first taken off. Indeed, it is found that frosty weather interferes materially with the operation of hardening.

Some workmen maintain that the hardening is done better if the water has been long used for the purpose without renewal.

TEMPERING.

=88.= Hardened steel is extremely fragile, but its tenacity may be restored by _tempering_, that is to say, by heating it to a degree dependent on the amount by which its original softness has to be restored. The color of the metallic surface will gradually change as the temperature rises, each tint corresponding approximately to the degree of heat given in the following table (Stodart):

1. Very pale straw yellow 220° C. (430° F.) } 2. A shade darker yellow 235° C. (450° F.) } Tools for metal. 3. Darker straw yellow 245° C. (470° F.) } Tools for wood and 4. Still darker straw yellow 255° C. (490° F.) } screws, taps, etc. 5. Brown yellow 260° C. (500° C. 500° F.) } Hatchets, chipping 6. Yellow, tinged slightly } chisels and other with purple 270° C. (520° F.) } percussive tools, 7. Light purple 275° C. (530° F.) } saws, etc. 8. Dark purple 290° C. (550° F.) } 9. Dark blue 300° C. (570° F.) } Springs. 10. Paler blue 310° C. (590° F.) } 11. Still paler blue 320° C. (610° F.) } Too soft for the 12. Still paler blue, with tinge } above purposes. of green 335° C. (630° F.) }

=89.= It will facilitate the precise determination of these points if it be remembered that

An alloy of 1 part lead and 1 part tin (by weight) melts at 196° C. (385° F.) Metallic tin ” ” ” 230° C. (446° F.) An alloy of 2 parts lead and 1 part tin ” 240° C. (465° F.) Metallic bismuth ” ” ” 270° C. (520° F.) An alloy of 5 parts lead and 1 part tin ” 290° c. (550° F.) Metallic cadmium ” ” ” 310° C. (590° F.) Metallic lead ” ” ” 320° C. (608° F.)

=90.= Before proceeding to temper an object, at least one of its faces must be smoothed with pumice-stone, oilstone dust, or emery paper, and the surface must be left perfectly clean, care being taken to avoid contact with the fingers, as otherwise it will be difficult to ensure the requisite tint being obtained.

Tempered to any shade between Nos. 1 and 6 the steel will, if previously well hardened, be left too hard to be worked by a file or graver; heated beyond No. 10, it can no longer be much bent without distortion.

When the quality and the degree of hardness of steel differ, the temper corresponding to a given tint will also vary. As a rule, hardened cast steel, tempered to No. 8, will be found as soft as natural steel which has been let down to No. 9, or even to No. 10.

A piece of steel can be let down to the same tint several times in succession without altering its properties.

If a good and uniform color is desired, the steel must be highly polished, as the oxidation of rough parts will render the tint irregular. The rouge employed must not be too dry, and, if the burnisher is used, care should be taken that it acts on the entire surface. Metal of a bad quality, which will not take an even polish, can rarely be nicely blued.

When the object is finely _smoothed_ with a uniform white surface, very good results may be obtained; but in such cases the cleaning must be carefully conducted, as the presence of minute greasy particles will always render the color irregular, and may even entirely prevent its appearance.

A uniform color can only be obtained by heating the object in such a manner that its temperature is raised evenly throughout.

The tempering may be performed by placing an object on the _bluing tray_, a thin metallic plate, often covered with a thick layer of fine brass filings, which should be renewed for each operation; or on a thick piece of metal previously heated to a sufficient degree; on ignited charcoal covered with a layer of white ash; in a bath of molten metal, the temperature of which corresponds to the requisite degree of heat, or the object may be laid on the surface of such a bath, etc. Some watchmakers when letting down a piece of steel immerse it in water to check the action; but by so doing they produce an exactly contrary effect. If a piece of steel be cooled suddenly in water as soon as it assumes any given color it will be _softer_ than if left to cool in the open air (=78=).

At one of the blue tints, steel possesses its _maximum elasticity_. The exact shade varies with the different qualities of steel.

If a hardened and tempered spring has lost its initial elasticity, this may be restored or even improved upon by gently hammer-hardening, and after whitening with emery, again tempering to the proper blue tint.

=91.= A very convenient way of tempering a large number of small articles at a time, heating them with absolute uniformity, is to place them in a small vessel with sufficient tallow or cold oil to cover them; the whole is then heated to the requisite degree, which may be determined by a thermometer or by observing the smoke. When smoke is first seen to rise, the temper corresponds to No. 2 in the table (article =88=). Smoke more abundant and darker corresponds to No. 5. Black smoke still thicker, No. 7. Oil or tallow takes fire with lighted paper presented to it, No. 9. After this the oil takes fire of itself and continues to burn. If the whole of the oil is allowed to burn away, the lowest temper in the table is reached.

It is often convenient to simply smear an article with oil or tallow, and hold it over a flame or piece of hot iron. The temper can then be judged in the manner just explained.

With a view to combine the two operations of hardening and tempering, M. Caron suggested that the temperature of the water used for hardening be heated to a pre-determined degree. Thus the requisite temper may be given to gun-lock springs by heating the water in which they are hardened to 55° C. (130° F.).

TO WHITEN AND BLUE STEEL.

=92.= Some makers of watch-hands and balance-springs, when they are not satisfied with the color assumed by an object in tempering, immerse it in an acid bath, which whitens it, after which the bluing operation is repeated.

We have seen watchmakers whiten small pieces of steel with a piece of pith moistened with dilute sulphuric acid, but the method cannot be recommended.

Others fix fine steel work, a watch-hand for example, with wax on a plate, and whiten it by means of pith and polishing rouge, or a small stiff brush charged with the same material. It is then detached, by heating, and cleaned in hot alcohol.

These methods, if judiciously employed, are of great service, but it is important to remember always to thoroughly wash after the use of acid, and then to allow the object to remain for a few minutes in alcohol.

Sulphuric acid does not whiten well. It often leaves dark shades on the surface. Hydrochloric acid gives better results.

=93.= =To blue steel uniformly.= In order to secure a uniform color in tempering or bluing, it is essential that the smoothing and polishing should have been very evenly done. The surface must be perfectly clean; for otherwise parts that are greasy, or on which the rouge has remained too long, or has been too dry, will not exhibit the same tint as the rest. The heat must be uniformly distributed. This is why, when bluing screws in a perforated bluing pan, it is customary to lightly strike the handle, for the vibration and the perpetual change in the contacts ensures their receiving the heat more evenly. A similar purpose is served by placing the pieces in brass filings. Steel must not be tempered while only in contact with bodies that are bad conductors of heat, stone, either in powder or block, for example; because, as we have already observed, the distribution of heat would occur unevenly throughout the metal.

Watchmakers secure a uniform tint more easily by using an iron or copper polisher than one of any other metal.

=94.= _To blue small pieces of steel evenly._ If the foregoing precautions are carefully observed, the following methods will give satisfactory results:

First blue the object without any special regard to uniformity of color. If it proves to be imperfect, take a piece of dead wood that does not crumble too easily, or of clean pith, and whiten the surface with rouge without letting it be too dry. Small pieces thus prepared, if cleaned and blued with care, will assume a very uniform tint.

A clever mechanic assures us that he easily obtains a similar result by rubbing the surface, after it has been well smoothed, with the end of a stick that has been partly burnt in the fire.

=95.= _To blue a clock hand or a spring._ To blue a piece of steel that is of some length, a clock hand for example; clockmakers place it either on ignited charcoal, with a hole in the center for the socket, and whitened over its surface, as this indicates a degree of heat that is approximately uniform, or on a curved bluing tray perforated with holes large enough to admit the socket. The center will become violet or blue sooner than the rest, and as soon as it assumes the requisite tint, the hand must be removed, holding it with tweezers by the socket, or by the aid of a larged-sized arbor passed through it; the lower side of the hand is then placed on the edge of the charcoal or bluing tray, and removed by gradually sliding it off towards the point, more or less slowly according to the progress made with the coloring; with a little practice, the workman will soon be enabled to secure a uniform blue throughout the length, and even, if necessary, to retouch parts that have not assumed a sufficiently deep tint.

Instead of a bluing tray, a small mass of iron, with a slightly rounded surface and heated to a suitable temperature, can be employed; but the color must not form too rapidly, and this is liable to occur if the temperature of the mass is excessive. Nor should this temperature be unevenly distributed.

A spring after being whitened can be blued in the same way. Having fixed one end, it is stretched by a weight attached to the other end, and the hot iron is then passed along it at such a speed that a uniform color is secured. Of course the hot iron might be fixed and the spring passed over it. A lamp may be used, but its employment involves more attention and dexterity.

=96.= =Bluing as an indication of temper.= This subject has already been very fully considered in article =88= to =90=. When the color assumed by a piece of steel does not require to be preserved, and it is only necessary to temper the object at a certain temperature, the means best adapted to expedite the operation will naturally be sought. Thus, in factories, large numbers are tempered at once in a bath of tallow, oil, etc. The workman, in judging temper by color (=88=), must have enough experience to enable him to determine, for a given sample of steel, what are the successive colors as well as the temperature of the bath, etc. His success is certain; but it depends on the experience, and, therefore, on the sense of sight of the operator, and, we should again add, on the knowledge he possesses of the qualities of the steel he is using.

CASE-HARDENING.

=97.= This process is often resorted to when a hard surface is required on objects of wrought iron, for example the face of an anvil. It is the exact converse of the method already described in article =59= for obtaining malleable castings, and consists in heating the object to a red heat in contact with charcoal, or some substance containing carbon; this enters into the surface iron, converting it into steel. Or after heating to a bright redness the object may be sprinkled over with prussiate of potash, returned to the fire, and after a few minutes cooled by immersion in water. When a greater thickness of steel is needed, or when dealing with large articles, they must be enclosed in wrought-iron boxes, and bedded in such substances as fragments of horn, bones, leather cuttings, etc; the box is then luted up and the whole maintained at a red heat for twelve hours, after which the fire is allowed to die out. Articles may sometimes be case-hardened by coating with a paste of arsenious acid, powdered leather, horn, or other nitrogenous body and hydrochloric acid, and then heating them to bright redness in a muffle or other suitable furnace.

INFLUENCE OF FOREIGN METALS AND METALLOIDS ON THE QUALITIES OF IRON AND STEEL.

=98.= It would be impossible to give a full account of this subject in the space at our disposal, and the reader must be referred to works on the metallurgy of iron and steel for details in regard to the remarkable influence of minute traces of phosphorus, tungsten, silicon, manganese, arsenic, etc., on the mechanical and chemical properties of those metals.

COPPER.

=99.= Copper is an elementary body of a reddish-brown color, which must not be confounded with brass, occasionally termed yellow copper. In tenacity it comes next below iron, breaking with a strain of 34 kilo. per sq. mm. of section (or 48,000 lbs. per sq. inch).

In horology, the only use made of the pure metal is for the construction of compensation pendulums on the gridiron principle, and as wire in electric clocks. It is also employed, when rolled into thin sheets, for a base to receive the enamel of watch dials, in consequence of its expansion being about the same as that of the enamel, which does not therefore crack in the cooling.

The copper of commerce is seldom pure, and this gives rise to many of the imperfections met with in ordinary brass.

ZINC.

=100.= This is an elementary metallic body of a bluish white color. It is used in the form of rods, for compensation pendulums.

It must be obtained of great purity, whether it is employed by itself or to alloy with another metal. The presence of foreign bodies in zinc, even in very small quantities, has a marked influence on the physical properties of an alloy into which it enters.

The purer the metal the more easily will it roll, and this fact can be taken advantage of as a test of quality.

Although very brittle at 0° C. (32° F.) and 200°C. (400° F.), it has a maximum malleability at about 100° C. (212° F.), the boiling point of water; it should, then, be heated to this degree before bending, rolling, hammering, etc.

It may be annealed in boiling water, or by heating to such a temperature that water hisses when allowed to drop on to it.

It melts at 420° C. (790° F.) and volatilizes if raised to a red heat.

A sudden cooling, or the presence of arsenic or antimony, will render zinc brittle. It must not be melted in cast iron vessels, as the quality of zinc is deteriorated by the small quantity of iron it takes up under such circumstances.

This metal possesses a great affinity for oxygen, and therefore oxidizes very readily when fused.

It is usual, before pouring zinc that is intended for rolling, to throw some pieces of the solid metal into the molten mass, the object being to somewhat reduce the temperature, and thus prevent a too rapid cooling, as, in that case, zinc is very brittle.

BRASS.

=101.= Pure copper is difficult to work with the graver or file, but such is not the case when this metal is alloyed with zinc; we then obtain brass, or, as it is sometimes termed, yellow copper.

Alloys containing copper, zinc, and tin are termed bronzes.

If a small quantity of lead, about 1 per cent. of its weight, be added to brass, it renders the metal less fibrous, imparting to it a certain degree of brittleness so that it is more easily worked with the graver, file, drill, or the saw.

When the brass is required to be hammered, a portion of the lead is replaced by tin; by this means the metal becomes more malleable, or, in terms of the workshop, soft.

The color, tenacity, ductility, malleability, etc., vary with the percentage composition of the alloy. It is, then, of the utmost importance that a watchmaker be able to test and select the brass before employing it in his work; metal that is excellent for wire-drawing, for example, would be utterly useless for making an escape wheel, since it would become distorted in the cutting in consequence of its ductility. It belongs, in fact, to the class of metals that will extend under the hammer without hardening (very soft brasses).

The following is given as an analysis of brass very frequently employed in horology: copper, 66 per cent., zinc, 33 per cent.; and lead, 1 per cent. But it must not be forgotten that this is only to be taken as a mean. Both the proportions and the qualities vary with different makers, doubtless also according to the degree of purity of the metals employed in their manufacture.

=102.= =To select brass.= By following the directions given below any watchmaker should be able to select the brass best suited to his special requirements.

When the copper is in excess, zinc being proportionately reduced, the brass is usually soft and of a beautiful golden color. On the other hand, as the proportion of zinc is increased, the brass becomes more and more brittle, and at the same time, more fusible; the color changes to a light yellow, ultimately becoming greyish-white, and brass of this nature is said to be “hard.”

Very soft brass chokes the file, and spreads without hardening under the hammer; very hard brass, on the other hand, is fragile, liable to crack when hammered cold, and breaks in passing through the draw-plate.

Metal of a good yellow shade, intermediate between the golden and the pale yellow color, passes well through the draw-plate, spreads out slowly under the hammer, but without cracking, until of about half the initial thickness, and then resists the further action of the hammer, which rebounds from it; such brass is usually found to be of good quality for watchwork.

A sheet of brass is rarely homogeneous. If, after pouring, the metal has been allowed to cool slowly, the interior will be crystalline, and there will be an uneven fracture. This will cause the tenacity, etc., to vary throughout the mass. Similar differences are occasionally to be observed between the two faces of the same plate, due to the phenomenon of _liquation_; that is to say, to a tendency that characterizes certain metals when melted together to separate from one another when the cooling is not affected under proper conditions.

If the two surfaces of a plate be scraped clean at several points, and drops, as nearly equal as possible, of very pure watch oil, be placed on these clean surfaces, it may be taken as a rough indication that the metals are uniformly distributed if the successive shades of color of the oil as time goes on are the same at all the points experimented upon.

Some watchmakers heat the brass to a red heat (which must never be exceeded), and plunge it into nitric acid (equal parts acid and water). By this means the entire surface is cleaned, and the above examination is facilitated.

HAMMER HARDENING OF BRASS.

=103.= =Plates.= The selection of the metal will depend on the purpose for which it is intended, and the thickness must be such that, when hammered till of sufficient hardness, it will approximately equal one dimension of the required object; for it is advisable to remove as little of the surface metal as possible, a plate always hardening much more at the surface than in the interior.

There is considerable difficulty in indicating clearly in a book the exact mode of conducting the operation of hammer-hardening, and the assistance of a competent master is essential, at any rate for the first few trials. It must suffice to point out that the anvil, with a slightly convex surface, and the hammer, of sufficient weight, must be in very good condition and, if possible, polished on their faces; the head of the latter should be rather convex, and the pene or chisel end somewhat broad and gently rounded off in all directions, for it will be needed as a means of bending the metal upwards; the curvature being such that there is not a danger of starting a crack, etc., by its means. We have already spoken of these two tools (=79=, =80=); it is only necessary to add that a thick straw pad should be placed under the anvil or block.

When one is compelled to use brass that is too thick, so that there is much work to be done with the hammer to reduce the thickness to what is required, it is a good plan to commence by elongating the metal in one direction, striking with the pene of the hammer a series of parallel blows in the direction of the required elongation; when the thickness is two or three times that ultimately needed, the surface is smoothed with the hammer-head and annealed; then it is brought to the right thickness by another hammering in the manner explained below, but it should be again pointed out that, when possible, metal of a suitable thickness ought to be taken in the first instance, since too much hammering has a detrimental effect.

Before hammer-hardening a plate, it must be dressed, an operation which consists in rounding off the edges very carefully in order to prevent their cracking, and in rounding the bottom and sides of internal angles which, without such a precaution would occasion a rupture. After this is completed, proceed to the hardening, using a rather heavy hammer, and giving sharp blows along lines parallel to the sides of the plate; commence from one of the corners in the case of a square plate; and with a round plate let the blows be in circles. In the latter case, work from the circumference towards the center, at the same time gradually increasing the force of the blows, since the metal opposes a greater resistance towards the center. If the work is done evenly and without hurrying, the surface will remain fairly flat, a fact which should be verified from time to time by the aid of a metal rule.

Round plates are sometimes hardened by commencing to hammer in the center and working towards the circumference along two radii in opposite directions; that is along a diameter. This first diameter is then crossed by another at right angles; the intervals are filled in with other diameters that must not touch until the entire surface is covered, always taking care to work from the center towards the circumference.

When the metal is thin only the hammer-head is used, but beyond a certain thickness the pene of the hammer must be employed until about half the required thickness is reached; the surface is planished and the hardening finished with the face.

Blows that are irregular, too hard or roughly given, will cause the metal to crack. Hurried working will disturb the molecular grouping of the alloy; it will at the same time be heated and therefore softened, thus losing all the good qualities that are anticipated from hammer-hardening, namely increased body and elasticity. It was in order to avoid this heating that the old watchmakers used to hammer the brass in cold water, an excellent precaution which is too much neglected at the present day.

Brass that is badly hammered, the blows being violent or irregular, will spring out of shape on being cut and occasionally crack when gilding.

If during the process of hammering, a crack is observed to be commencing at the edge, it must be removed with a rat-tail file, all sharp angles being rounded off; and when cracks immediately reappear on continuing the operation, it is an indication that the metal cannot support any further hammering cold.

If brass is compact or well forged it may be relied upon to preserve the oil at pivots, etc., better, as oil is decomposed more rapidly in presence of a finely divided metal.

=104.= =Brass rods.= Rods having a square section must only be hammered on two opposite faces.

A rod of square section can be hammered on all four faces but it must be first filed perfectly square; the hammering must not be pushed too far, and the four angles must be maintained right angles. If some are made obtuse and others acute, a flaw will be produced in the direction of a diagonal.

The three following methods are employed in the case of round rods:

The first consists in hammering over the entire surface, the rod being at the same time rotated on the anvil by hand; but this operation must not be much prolonged, as the metal is liable to crack lengthwise.

The second method consists in reducing the diameter of an annealed brass rod to about one-half or two-thirds its initial amount by causing it to pass in succession through a number of holes of the draw-plate.

When the third method, which is due to Brocot, is adopted, one extremity of the brass rod is gripped in the bench vise and the other end in a hand vise, which is then caused to rotate round the rod as an axis. If the torsion be continued until the metal is on the point of breaking, it will be found to be very effectually hardened. This method is resorted to with advantage for hardening pin-wire and the metal for making pillars.

TO ANNEAL BRASS.

=105.= When it is necessary to considerably reduce the dimensions of a piece of brass, either with the hammer, rolls or draw-plate, it must be annealed from time to time.

The metal should not be heated to redness; it is supposed, rightly or wrongly, that such a proceedings especially if repeated, separates a portion of the zinc, or at least changes the mode in which it is associated with the copper. Brass should be heated slowly and uniformly, in a moderate fire, until the temperature is such that drops of water thrown onto the surface are rapidly converted into vapour, or paper turns yellow and begins to smoke. It is then withdrawn from the fire and allowed to cool.

Brass is brittle when hot, so that it can only be worked cold.

When brass is annealed, just as when steel is tempered, the metal should not be allowed to rest on a bad conductor of heat, such as wood or stone, because there will be a tendency to uneven distribution of the heat throughout the metal.

CAST BRASS.

=106.= This is usually brittle, owing to the fact that the copper employed in its manufacture consists, as a rule, of all sorts of scrap, from good or bad metal; moreover, from motives of economy, the proportion of zinc is generally increased and, in pouring, the precautions essential to avoid the effects of liquation (=102=), etc., are frequently neglected. Such an alloy must never be used for small objects, it must be entirely excluded from a watch, and in a clock only such pivots as are called upon to perform an insignificant amount of work should be allowed to run in it.

In order to avoid injuring the file, or embedding in the metal any

## particles of the hard coating of oxide that always covers rough

castings, it is usual to dip the object in dilute nitric or sulphuric acid (=155=), by which the oxide is dissolved.

TIN.

=107.= This is an elementary body, almost as white as silver and having a breaking strain of only 8 kilo. per sq. mm. of section (or 11,300 lbs. per sq. inch.)

Watchmakers use it in making solder. It is also sometimes used in the form of plates or rods for polishing with rouge, and it is said to be much more efficient when very pure.

If a strip of pure tin is bent, a crackling noise, termed the “crying” of tin, is heard. After frequent bending, the metal loses this property.

The degree of purity may be judged:

(1) By the loudness of the “cry,” which is found to be greater as the tin is purer;

(2) By the relative lightness of two balls of equal size, one of which is formed of very pure tin and used as a standard;

(3) By pouring the metal, when just melted, in a mould 1 or 2 centimetres (about ¾ inch) in diameter. If tin is pure, when cast into plates or ingots, the surface will be perfectly smooth, without exhibiting any sign of crystallization at the moment of solidification, whereas the presence of small quantities of foreign metals causes it to be covered with a network of needle-formed crystals, which are the more numerous according as the metal is less pure.

The Banca tin is almost chemically pure; English tin is also very pure; but others contain a small percentage of copper, lead, iron, or arsenic.

BRONZE.

=108.= Bronze is an alloy, in very variable proportions, of copper and tin, to which may be added, according to circumstances, a small percentage of lead or zinc, or even iron, when it is desired to increase the hardness or tenacity.

As a rule, this alloy is tough and hard to work; it is especially used for parts of large machines that are subjected to considerable pressure.

The fusion and casting of bronze require special precautions, for the proportion between the metals is liable to vary through oxidation of the tin, which then goes to form a dross, and the composition may vary throughout the mass. It sometimes results from this that the bronze bearings for the pivots in large clocks are not even as good as ordinary brass, and wear away more rapidly than the pivots.

Bronze is also used by watchmakers for making plates or small rods for polishers, and for the bells of clocks. Bell-metal contains about 78 per cent. of copper and 22 per cent. of tin; it has a beautiful fracture, and is very fusible and sonorous. The addition of any other metal is rather prejudicial than otherwise; this explains why so many clock bells are wanting in sonorousness.

An impediment to the use of bronze is its want of malleability; but Dronier has recently pointed out that such alloys may be rendered perfectly ductile and malleable by adding from ½ to 2 per cent. of mercury. These alloys are said to be less oxidizable than ordinary bronzes, and at the same time more hard, elastic, resisting and sonorous.

STERRO.

=109.= This is an alloy containing 56 per cent copper, 41 zinc, 2 tin and 1 iron. It resembles a reddish-colored brass, and has been much used in Vienna, where it is considered superior to brass from the point of view of ductility, tenacity and malleability.

An experienced horologist, M. Grossmann, made satisfactory lever escape-wheels of it, and he considers it to be superior to the best brass in regard to both density and elasticity. At the same time he points out that it clogs the cutter, and the color is inferior to that of good hard brass.

LEAD.

=110.= A metal with a brilliant bluish grey lustre, which rapidly becomes dull when exposed to the air. It is very malleable and ductile. It breaks with a strain of 2.9 kilo. per sq. mm. section (4,000 lbs. per sq. inch), but possesses extreme flexibility.

Lead is not used in horology, except as a constituent of solders; in these, however, it plays a very important part. It is occasionally used in the pure state as a lap for applying polishing materials, but more frequently alloyed with tin, by which hardness is imparted to the metal, the alloy being known as “pewter.”

NICKEL.

=111.= An elementary metallic body of a greyish-white color, resembling that of platinum. With care it can be forged when hot and formed into plates; its structure in that case is fibrous. Its hardness is the same as that of iron, and nickel will take a high polish. Next to iron, it is the most powerfully magnetic of all metals.

It can be caused to alloy with many other metals—notably iron, cobalt, copper, zinc, tin, and antimony. According to Stodart and Faraday, an alloy of 33 parts iron and 1 part nickel is as malleable as the former metal, but less liable to rust. Fleitmann has recently shown that by the addition of about 1-10th per cent of magnesium, nickel is rendered perfectly malleable and ductile, capable of being drawn into wires or rolled into sheets, and Garnier finds that 3-10ths per cent of phosphorus has a similar effect.

Nickel is useful as a coating for objects that are not subjected to friction, for preserving them from the action of the air. It takes a beautiful polish, and is not tarnished by being touched.

GERMAN SILVER.

=112.= Although the proportion of copper in this alloy is considerably greater than that of nickel, watchmakers frequently apply the latter name to it, doubtless on account of the beautiful polish of which the metal is capable and the comparative inoxidizability which it derives from the presence of nickel.

German silver is an alloy of copper, nickel and zinc, with the occasional admixture of a small proportion of iron or tin. When used in the construction of objects that require soldering, 2 per cent. of lead is added.

The alloy usually employed in horology is very malleable; it has a mean composition: copper, 60 per cent; nickel, 20 per cent; and zinc, 20 per cent. That containing 58 per cent copper, 14 nickel, 25 zinc, and 3 iron, is said to be highly elastic.

The following useful details with regard to the employment of German silver for watchwork are due to M. C. E. Jacot.

Watch movements have been made of this alloy for the past thirty years; it was long thought that the taste would die out, but, on the other hand, the demand for “nickel” movements increases each year.

The alloy is better prepared at the present day; it has a beautiful grayish-white colour, it is more malleable, and better to work than formerly, but still not so easy as brass. The latter alloy is less detrimental to the file, and can be turned and drilled more rapidly.

German silver is only used for the plates, cocks and bars. The barrels and wheels are of brass, and surfaces exposed to friction, such as the center pivot-hole (all other holes being jewelled) are bushed with the same metal, for it is observed that in presence of nickel oil is rapidly blackened and the pivots wear sooner than when working in good brass.

The color remains unaltered for a long time if the surface has been carefully smoothed in the first instance; and if cleansed with soap and water, its original freshness can be to a great extent restored. Some watchmakers prefer to employ chemical preparations for cleaning the metal.

The following is recommended as very effective for this purpose: Mix 50 parts alcohol, 1 part sulphuric, and one part nitric acid. Allow the pieces to remain in this liquid for 10 or 15 seconds, wash with cold water, and subsequently with alcohol, dry with a soft rag or in boxwood saw dust.

GOLD.

=113.= An elementary body, the most beautiful and the most valuable of all the ordinary metals. In the unalloyed state it has a pure yellow color, and when reduced to extremely thin leaves, appears green by transmitted light. It is the most malleable and ductile of all the metals, but its tenacity is low.

Gold resembles platinum, silver, iron, etc., in being capable of welding, that is to say, two pieces of the metal can be united without previous fusion. Indeed, by the application of great pressure it can be made to weld when cold.

It is insoluble except in aqua regia (a mixture of 1 part nitric acid and 4 parts hydrochloric acid), alkaline persulphides and selenic acid. Chlorine, phosphorus, and a few other substances can be made to combine with it by the acid of heat.

It is as a preservative, that is applied in layers termed “gilding,” that gold is principally used in watchwork, and some details will be found on this subject under “Gilding,” (articles =142=-=153=). Owing to its softness the metal is not used in a pure state, but usually alloyed with copper. The principal alloys in use in this country are:

22 parts (carats) gold, 2 parts (carats) copper, for coin and wedding rings.

18 parts gold, 6 parts copper, for high-class jewelry and watch-cases.

15 parts gold, 9 parts copper, for ordinary jewelry.

12 parts gold, 12 parts copper; and 9 parts gold, 15 parts copper, for common jewelry.

The alloys used for soldering gold will be described under “Solders” (=126=).

Alloys of gold with silver and copper have been employed for making watch wheels; they wear well, and will take a beautiful polish, which is maintained for a longer time than in the case of brass wheels.

Chronometer balance-springs and the suspension-springs for astronomical clocks have also been made of gold-copper or gold-silver alloys rolled and hardened (=591=.) If carefully prepared, they maintain their elasticity unimpaired for a long period, and there is no liability to rust.

The dilatation for a given change of temperature is, however, greater than that of steel, so that a greater compensating effect becomes necessary, but this inconvenience is partially compensated for by its inoxidizability and the fact that it is not liable to become magnetic.

SILVER.

=114.= This metal in an unalloyed state is too soft for use in horology; its principal use is for cases, and as a constituent of solders.

Houriet made watch wheels of an alloy containing 2 parts silver to 1

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