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
part 18-carat gold, and he affirmed that this alloy became polished at
the acting surfaces of the teeth. Jurgensen states that chronometer
escape-wheels made of this alloy, carefully hammered, do not require
oil at the points of their teeth.
Dumesnil proposed an alloy of 2 parts copper, 1 part silver, and 1 part
zinc, all perfectly pure. Lecocq made chronometer balances in which the
brass was replaced by pure silver deposited on the surface of the steel
by electrolysis, thus avoiding the use of a fire. The compensation is
said to have been very efficient.
ALUMINIUM AND ALUMINIUM BRONZE.
=115.= Aluminium is an extremely light elementary body, having a
density of only 2.56; with equal bulks, therefore, it will weigh only
about as quarter as much as silver. As its capacity for heat is very
great, this metal is observed to heat or cool more slowly than other
metals.
Pure, or in a slightly alloyed state, it has not been used in horology,
except for pendulum rods and large hands in regulator clocks; in short,
it can be employed where lightness is the principal quality in view.
It is extremely ductile. The presence of 1-100th part of bismuth,
however, renders the metal somewhat brittle, and it develops cracks
under the hammer. Traces of iron also decrease its malleability.
An alloy of 5 parts silver and 95 aluminium can be as easily worked as
the pure metal, but is harder and takes a better polish.
We would add a curious observation of M. Redier: After passing a piece
of aluminium several times through the draw-plate, he observed that the
elongation had only occurred at the surface; for on cutting the wire at
different points, he noticed that, throughout a portion of the length,
the metal was hollow, a very fine capillary tube being thus formed.
=116.= _Aluminium Bronze_ is an alloy of aluminium with copper. A
alloy of 5 parts of the former to 95 of the latter has a beautiful
golden color, but if the proportion is changed to 10 and 90 parts
respectively, we obtain the most serviceable and the most easily worked
alloy.
This bronze can be forged at a cherry-red heat, and even near its
melting point; and its thickness can be reduced to a very small amount
under the hammer. It is easily filed and turned, but does not possess
any special advantage over brass, which is less detrimental to the
file; the density is 7.7, very little below that of brass, 8.4.
It appears from a considerable number of experiments that it might
be used with advantage for the bearings of axes that rotate with
high velocities. It resists wear better than any other metal. In the
experiments made by Foucault to demonstrate the rotation of the earth
by means of the pendulum, he found that an aluminum bronze wire lasted
for the longest period. Its tenacity is equal to that of iron. It has
been shown that slide-bars of locomotives made of this bronze resist
wear twice as long as those formed of the ordinary bronze. There would
then be an advantage in using it for the bearings of foot-lathes, etc.
Grossman asserts that lever escape-wheels of this metal have proved
satisfactory, and he makes the following observation on the subject. If
aluminium bronze be reduced to three-fourths of its original thickness
by hammering, it will begin to crack. This can be prevented by heating
to a red heat and plunging into water; it can then be again reduced by
one-fourth of its thickness, and again annealed, and so on. He reduced
the thickness from 2.5 millimeter to 0.2 millimeter, and the metal
resisted for a long period repeated flexures backwards and forwards;
and he observes that no other metal, after being so much compressed,
would possess the same marvellous degree of tenacity.
In order to obtain aluminium bronze of the best quality, the copper
should be absolutely pure, and, in the manufacture, the alloy must be
melted and forged two or three times in succession, as by this means
the strength and tenacity are increased, and the metal can be more
easily worked.
The beautiful golden color possessed by certain of these bronzes when
polished, has caused them to be used for cheap watch-cases, but they
always tarnish at those parts that are not subject to daily wear.
MERCURY.
=117.= This is the only metal liquid at the ordinary temperature; it
solidifies at -40° C. (-40° F.). It possesses a high metallic lustre,
resembling silver, but with a slightly bluish tint, and does not
oxidize at ordinary temperatures.
Mercury alloys with many other metals, forming amalgams, and as small
a quantity as 1-40th per cent of lead suffices to entirely alter its
character. The presence of such traces can be easily detected by the
liquid wetting glass or china, and therefore forming a tail when a
vessel containing it is tilted.
The commercial metal is rarely pure, but the greater portion of the
lead, tin, bismuth or copper, by which it is contaminated, can be
removed by distillation. The most convenient method consists, however,
in agitating the metal with either dilute nitric acid, a solution of
mercurous nitrate, strong sulphuric acid, a solution of corrosive
sublimate or of perchloride of iron, and subsequent washing with
distilled water. When mercury is only contaminated with mechanical
impurities, they can be very effectually removed by agitating with
powdered loaf sugar.
This metal has many uses in the arts, for the construction of
thermometers, barometers; for plating, etc.; in horology it is used
for compensation pendulums, and has also been occasionally used for
compensation balances.
PLATINUM.
=118.= This elementary body is almost as white as silver, takes a
brilliant polish, and is highly ductile and malleable. It is the
heaviest of the ordinary metals, the least expansive when heated, and
has a breaking strain of 40 kilo. per sq. mm. section (56,500 lbs. per
sq. inch.).
Platinum is infusible, except at the high temperatures attainable with
the oxy-hydrogen blow-pipe. At a white heat, however, it softens,
and can be forged and welded. It is unacted upon by the air at any
temperature, and is insoluble in acids, except aqua regia (=155=),
although acted on by certain alkalies.
This metal is used in the construction of scientific instruments, and
for objects that are exposed to the air, as, for example, sun dials.
Alloyed with irridium, (a rare metal of the same group) it possesses an
excellent and unalterable surface for fine engraving, as the scales of
astronomical instruments, etc. This alloy has also been adopted for the
construction of international standards of length and weight.
Platinum is much employed for chemical apparatus, in consequence of its
being unacted on by acids, and its non-liability to melt in ordinary
furnaces. Both the pure metal and its alloys with silver have been
employed in the form of wire for bushing the pivot-holes of watches,
and in sheets for cutting out cocks and wheels, but the results
obtained were not as good as with good brass. As a rule, such wheels
are found to occasion a rapid wear of pinion leaves.
Attempts have also been made to construct balance-springs of this
metal, but we are informed that they were not found to possess any
sufficient advantages.
It is advisable to heat platinum in a spirit lamp or Bunsen burner; the
naked flame is objectionable, because, being charged with a certain
amount of carbon, it deteriorates the metal.
PALLADIUM.
=119.= This metal resembles silver rather than platinum, and is almost
as infusible as the latter metal. It has a density of 12.5. When heated
in contact with air it becomes blue, owing to the formation of an
oxide. It possesses the remarkable power of absorbing (or _occluding_)
about 900 times its own volume of hydrogen, if attached to the negative
pole of a battery in acidulated water; its bulk is increased slightly
by this charge, and, on expelling the gas by the aid of heat, the
metal shrinks to less than its initial dimensions. Palladium is useful
for the graduated scales of scientific instruments, since it is not
discolored by sulphurous acid. It forms alloys with most of the metals
and some of these can be hardened like steel. If 100 parts of steel be
alloyed with 1 part of this metal, the resulting alloy is said to be
excellent for making scientific instruments, and an alloy of 24 parts
palladium, 44 silver, 72 gold, and 92 copper has been recommended for
use in horology.
M. Paillard, of Geneva, has introduced balance-springs made of an
alloy, whose composition is not given, possessing the following
advantages: they are non-magnetic, their tenacity is considerable, are
not tarnished by the air, sulphurous acid, or sea water; nor are they
distorted by heating, and, on cooling, they recover their original
elasticity, which is equal to that of steel hardened and tempered to a
blue color. The co-efficient of expansion of this alloy is rather less
than that of steel.
CHARACTERISTIC PROPERTIES OF ALLOYS.
=120.= _Density._ This is sometimes rather greater and sometimes less
than that deduced from the densities of the constituent metals,[4] but
no exact law has been discovered in regard to this question.
_Hardness, Ductility, Tenacity._ Alloys are usually harder, more
brittle, and less ductile and tenacious than the most ductile and
tenacious constituent metal.
_Elasticity._ The co-efficient of elasticity of an alloy generally
approximates closely to the mean of the co-efficients of its
constituent metals.
_Expansion._ The co-efficient of linear expansion of an alloy, that is
to say, the number representing the proportional part of its length
by which it increases for each degree rise of temperature, may be
approximately estimated as follows: multiply the linear co-efficient of
each constituent metal by the percentage of it present in the alloy,
and divide by its density. Add together the several numbers thus
obtained. Multiply this sum by the density of the alloy (which must be
experimentally determined) and divide by 100. The resulting figure is
the required linear co-efficient (=122=).
_Fusibility._ Alloys are always more fusible than the least fusible of
their component metals, and often more so than any one of them.
_Oxidation._ As a rule, the air acts with less energy on alloys than
on their constituent metals. There are, however, cases in which the
converse is the case.
_Action of acids._ This is generally similar to the action on the
predominating metal.
_Observations._ Alloys formed of metals that differ materially in
density are rarely homogeneous, especially if they have been allowed
to cool slowly. It is, then, essential that they be thoroughly stirred
and cooled rapidly. It is for this reason that alloys are frequently
poured out on to a flagstone to cool, or that they are compressed after
pouring, whereby the formation of crystals is prevented.
=121.= =Metals and alloys.= The following table gives the more
important physical properties of the metals and alloys generally met
with, and will be found useful for reference. The precise meaning of
each number may be gathered from the notes in paragraph =122=.
+-------------------+------------+----------+-----------------------+
| | Specific | Degree | Linear Expansion |
| METALS. | Gravity. | of | per |
| | (Water=1) | Hardness | 1° Fahr. 1° Cent. |
+-------------------+------------+----------+-----------+-----------+
|Aluminium (115) | 2.56 | -- | 0.0000123 | 0.0000222 |
| ” Bronze (116)| 7.7 | -- | -- | -- |
|Brass, Drawn (101) | 8.54 | -- | 0.0000107 | 0.0000193 |
| ” Cast (106) | 8.10 | -- | 0.0000104 | 0.0000187 |
|Bronze (108) | 8.40 | -- | 0.0000100 | 0.0000180 |
|Copper (99) | 8.94 | 2.5-3 | 0.0000102 | 0.0000183 |
|German Silver (112)| -- | -- | -- | -- |
|Gold (113) | 19.26 | 2.5-3 | 0.0000077 | 0.0000138 |
|Iron, Wrought (54) | 7.84 | 4.5 | 0.0000066 | 0.0000119 |
| ” Cast (58) | 6.9 to 7.5 | -- | 0.0000062 | 0.0000112 |
|Lead (110) | 11.33 | 1.5 | 0.0000167 | 0.0000301 |
|Mercury (117) | 15.60 | -- | 0.000101 | 0.000182 |
|Nickel (111) | 8.82 | 5 | [cubical | [cubical |
|Palladium (119) | 11.80 | 4.5-5 | -- | -- |
|Platinum (118) | 21.50 | 4-4.5 | 0.000005 | 0.000009 |
|Silver (114) | 10.57 | 2.5-3 | 0.0000111 | 0.0000190 |
|Steel (60) | 7.72 | 6-7(hard)| 0.0000057 | 0.0000103 |
|Sterro (109) | -- | -- | -- | -- |
|Tin (107) | 7.30 | 2.5-3 | 0.0000152 | 0.0000273 |
|Zinc (100) | 7.13 | 2 | 0.0000122 | 0.0000220 |
+-------------------+------------+----------+-----------+-----------+
+-------------------+---------------+---------+---------------------+
| | Specific Heat | Melting | Conductivity |
| METALS. | per Degree | Point. | for |
| | Cent. | | Heat. Electricity. |
+-------------------+---------------+---------+--------+------------+
|Aluminium (115) | 0.2143 | 1500° F.| -- | 56.1 |
| ” Bronze (116)| -- | [about| -- | -- |
|Brass, Drawn (101) | } 0.0939 | { -- | -- | -- |
| ” Cast (106) | } | { 1870° | -- | -- |
|Bronze (108) | -- | 1692° | -- | -- |
|Copper (99) | 0.0951 | 2000° | 73.5 | 99.8 |
|German Silver (112)| -- | -- | -- | 7.67 |
|Gold (113) | 0.0324 | 2610° | 53.2 | 78.4 |
|Iron, Wrought (54) | 0.1138 | 2900° | 11.9 | 16.8 |
| ” Cast (58) | 0.1298 | 1920° | -- | -- |
|Lead (110) | 0.0314 | 608° | 8.5 | 8.3 |
|Mercury (117) | 0.0333 | 39° | -- | -- |
|Nickel (111) | 0.1086 | -- | -- | 13.1 |
|Palladium (119) | 0.0593 | -- | 6.3 | 18.4 |
|Platinum (118) | 0.0324 | -- | 8.4 | 18.0 |
|Silver (114) | 0.0570 | 1832° | 100.0 | 100.0 |
|Steel (60) | 0.1175 | 2400° | -- | -- |
|Sterro (109) | -- | -- | -- | -- |
|Tin (107) | 0.0569 | 446° | -- | 12.4 |
|Zinc (100) | 0.0955 | 680° | -- | 29.0 |
+-------------------+---------------+---------+--------+------------+
=122.= =Notes on the foregoing table.= For a complete explanation of
the several properties of metals and alloys that are enumerated in the
above table, the reader must be referred to works on mechanics and
physics, but the following explanatory notes are necessary.
The number in brackets after the name of each metal, etc., refers to
the article in which it is considered.
The _specific gravity_ of a substance is the ratio of the weight of a
given bulk of that substance to the weight of the same bulk of water at
a definite temperature. The numbers here given can only be regarded as
approximations, as the specific gravity varies greatly with the state
in which a body exists, the hammering it may have been subjected to,
etc.
_Degree of hardness_ is ascertained by means of the following standard
series, observing which of them scratches the body under examination
and which it is capable of scratching.
1, Talc; 2, Gypsum; 3, Calc-spar; 4, Fluor-spar; 5, Apatite; 6,
Felspar; 7, Quartz; 8, Topaz; 9, Sapphire; 10, Diamond.
_Linear expansion._ These co-efficients represent the extension in
length that the several substances undergo when heated: the first
column for each degree Fahrenheit and the second for each degree
Centigrade. The extension is given per unit of length; thus, 1 inch of
copper at 32° F. will become 1 + 0.0000102, or 1.0000102 inch at 33° F.;
and 1 + 30 × .0000102, or 1.000306 at 32 + 30 or 62° F.
Superficial expansion may be obtained by multiplying the linear
co-efficient by 2, and cubical expansion by multiplying the same number
by 3.
As in the case of specific gravity, these data, as well as those in
succeeding columns, can only be regarded as approximations, depending
on the condition of the metal etc.
_Specific heat_ is the amount of heat required to raise the temperature
of a substance one degree (the Centigrade scale being here adopted),
that required for the same weight of water being taken as unity. The
corresponding numbers on the Fahrenheit scale can be deduced from those
here given by multiplying by 5 and dividing by 9.
The _melting points_ are given on Fahrenheit’s scale and can only be
regarded as approximate on account of the difficulty experienced in
determining these high temperatures. Different observers often vary by
two or three hundred degrees in their estimates.
_Conductivity for heat and electricity_ are given in reference to that
of silver, which is called 100. It surpasses all other known metals in
both these properties when chemically pure, but a trace of impurity has
a very prejudicial influence on them.
It will be observed that in many cases the conductivities have not been
determined, a remark that applies to other columns of the table.
SOLDERING.
=123.= It is well known that a _solder_ is an alloy employed to unite,
by the aid of heat, two metallic bodies that are placed in contact.
A solder, then, must be much more fusible than the metals it unites,
otherwise these latter would be damaged by the degree of heat applied.
Solder is all the less tenacious, and melts the more easily according
as the proportion of the most fusible metal present is increased.
This fact is taken advantage of when several solderings have to be
performed on the same object. The alloy last employed will require to
be considerably more fusible than the first, as otherwise the heat
would be so great that the earlier joints would melt. In an ordinary
lead-tin solder, the fusibility is increased by increasing the
proportion of the latter metal till the lead is to tin, as 6 is to 1.
This alloy melts at 194° C. (380° F.), and the melting point may be
still further reduced by adding a gradually increasing proportion of
bismuth.
As the melting point of the solder approximates to that of the metals
to be united, the risk of damaging these latter is of course increased,
but, at the same time, the joint will be all the stronger, as the metal
will be almost as strong there as at any other point, and it can be
forged, etc.
Solders are distinguished as _hard_ or _soft_; the former requires
the application of a red heat, and can therefore only be used for
such metals as gold, silver, brass; whereas the latter melt at very
low temperature, and can be employed for metals that have low melting
points, or when it is important not to exceed a moderate degree of
heat. The joint is, however, the more solid according as the heat
employed approximates to that at which the metal will melt.
=124.= =Composition of solders.= The solders ordinarily employed can
be obtained from material dealers, but it is advisable to give here
the composition of some of the more important, specifying the metal to
which they are applicable.
=125.= _Aluminium solders._ I. Zinc, 70 parts; copper, 15; aluminium,
15.
II. M. Mourey employes a series of aluminium-zinc alloys, commencing
with two per cent aluminium to 98 per cent zinc, and progressing to 20
per cent of the former to 80 per cent of the latter metal.
=126.= _Gold solders._ I. Gold, 6 parts; copper, 1 part; silver, 2
parts.
II. Gold, 15 parts; silver, 2 parts; copper, 1 part.
III. Gold, 11.94 parts; silver, 54.74 parts; copper, 28.17 parts; zinc,
5.81 parts. The three first metals are melted together in a crucible,
and when they have somewhat cooled, a rather greater proportion of zinc
than is here indicated (to allow for loss by volatilization) is added,
and the alloy constantly stirred.
=127.= _Silver solders._ I. Silver, 2 parts; brass (for pin-wire), 1
part.
II. Silver, 5 parts; pin-wire brass, 1 part.
III. Silver, 10 parts; pin-wire brass, 5 parts; pure zinc, 1 part.