metals. Thus, copper and zinc form brass, which has a different
density, hardness, and color from either of its constituents. Whether
the metals tend to unite in atomic proportions or in any definite ratio
is still undetermined. The evidence afforded by the natural alloys
of gold and silver, and by the phenomena accompanying the cooling of
several alloys from the state of fusion, goes far to prove that such
is the case (Rudberg). The subject is, however, one of considerable
difficulty, as metals and metallic compounds are generally soluble
in each other, and unite by simple fusion and contact. That they do
not combine indifferently with each other, but exercise a species of
elective affinity not dissimilar to other bodies, is clearly shown
by the homogeneity and superior quality of many alloys in which the
constituent metals are in atomic proportion. The variation of the
specific gravity and melting points of alloys from the mean of those
of their component metals also affords strong evidence of a chemical
change having taken place. Thus, alloys generally melt at lower
temperatures than their separate metals. They also usually possess more
tenacity and hardness than the mean of their constituents.
Matthiessen found that when weights are suspended to spirals of
hard-drawn wire made of copper, gold, or platinum, they become nearly
straightened when stretched by a moderate weight; but wires of equal
dimensions composed of copper-tin (12 per cent of tin), silver-platinum
(36 per cent of platinum), and gold-copper (84 per cent of copper)
scarcely undergo any permanent change in form when subjected to tension
by the same weight.
The same chemist gives the following approximate results upon the
tenacity of certain metals and wires hard-drawn through the same gauge
(No. 23):
Pounds
Copper, breaking strain 25–30
Tin, breaking strain under 7
Lead, breaking strain under 7
Tin-lead (20% lead) about 7
Tin-copper (12% copper) about 7
Copper-tin (12% tin) about 80–90
Gold (12% tin) 20–25
Gold-copper (8.4% copper) 70–75
Silver (8.4% copper) 45–50
Platinum (8.4% copper) 45–50
Silver-platinum (30% platinum) 75–80
On the other hand, the malleability, ductility, and power of resisting
oxygen of alloys is generally diminished. The alloy formed of two
brittle metals is always brittle; that of a brittle and a ductile
metal, generally so; and even two ductile metals sometimes unite to
form a brittle compound. The alloys formed of metals having different
fusing points are usually malleable while cold and brittle while hot.
The action of the air on alloys is generally less than on their simple
metals, unless the former are heated. A mixture of 1 part of tin and 3
parts of lead is scarcely acted on at common temperatures; but at a red
heat it readily takes fire, and continues to burn for some time like
a piece of bad turf. In like manner, a mixture of tin and zinc, when
strongly heated, decomposes both moist air and steam with rapidity.
The specific gravity of alloys is rarely {48} the arithmetical mean
of that of their constituents, as commonly taught; and in many cases
considerable condensation or expansion occurs. When there is a strong
affinity between two metals, the density of their alloy is generally
greater than the calculated mean; and vice versa, as may be seen in the
following table:
ALLOYS HAVING A DENSITY
Greater than the Mean of their Constituents:
Copper and bismuth,
Copper and palladium,
Copper and tin,
Copper and zinc,
Gold and antimony,
Gold and bismuth,
Gold and cobalt,
Gold and tin,
Gold and zinc,
Lead and antimony,
Palladium and bismuth,
Silver and antimony,
Silver and bismuth,
Silver and lead,
Silver and tin,
Silver and zinc.
Less than the Mean of their Constituents:
Gold and copper,
Gold and iridium,
Gold and iron,
Gold and lead,
Gold and nickel,
Gold and silver,
Iron and antimony,
Iron and bismuth,
Iron and lead,
Nickel and arsenic,
Silver and copper,
Tin and antimony,
Tin and lead,
Tin and palladium,
Zinc and antimony.
«Compounding Alloys.»—Considerable experience is necessary to insure
success in compounding alloys, especially when the metals employed vary
greatly in fusibility and volatility. The following are rules supplied
by an experienced workman:
1. Melt the least fusible, oxidizable, and volatile first, and then add
the others heated to their point of fusion or near it. Thus, if it is
desired to make an alloy of exactly 1 part of copper and 3 of zinc, it
will be impossible to do so by putting proportions of the metals in a
crucible and exposing the whole to heat. Much of the zinc would fly off
in vapor before the copper was melted. First, melt the copper and add
the zinc, which has been melted in another crucible. The zinc should be
in excess, as some of it will be lost anyway.
2. Some alloys, as copper and zinc, copper and arsenic, may be formed
by exposing heated plates of the least fusible metal to the vapor of
the other. In making brass in the large way, thin plates of copper are
dissolved, as it were, in melted zinc until the proper proportions have
been obtained.
3. The surface of all oxidizable metals should be covered with some
protecting agent, as tallow for very fusible ones, rosin for lead and
tin, charcoal for zinc, copper, etc.
4. Stir the metal before casting and if possible, when casting, with a
whitewood stick; this is much better for the purpose than an iron rod.
5. If possible, add a small portion of old alloy to the new. If
the alloy is required to make sharp castings and strength is not a
very great object, the proportion of old alloy to the new should be
increased. In all cases a new or thoroughly well-cleansed crucible
should be used.
To obtain metals and metallic alloys from their compounds, such as
oxides, sulphides, chlorides, etc., a process lately patented makes use
of the reducing qualities of aluminum or its alloys with magnesium. The
finely powdered material (e. g., chromic oxide) is placed in a crucible
mixed with aluminum oxide. The mixture is set afire by means of a
soldering pipe or a burning magnesium wire, and the desired reaction
takes place. For igniting, one may also employ with advantage a special
priming cartridge consisting of pulverized aluminum to which a little
magnesium may be mixed, and peroxide of magnesia, which is shaped into
balls and lighted with a magnesium wire. By suitable additions to the
pulverized mixture, alloys containing aluminum, magnetism, chromium,
manganese, copper, iron, boron, silicic acid, etc., are obtained.
«ALUMINUM ALLOYS.»
M. H. Pecheux has contributed to the _Comptes Rendus_, from time to
time, the results of his investigations into the alloys of aluminum
with soft metals, and the following constitutes a brief summary of his
observations:
«Lead.»—When aluminum is melted and lead is added in proportion
greater than 10 per cent, the metals separate on cooling into three
layers—lead, aluminum, and between them an alloy containing from 90 to
97 per cent of aluminum. {49} The alloys with 93, 95, and 98 per cent
have densities of 2.745, 2.674, and 2.600 respectively, and melting
points near that of aluminum. Their color is like that of aluminum,
but they are less lustrous. All are malleable, easily cut, softer
than aluminum, and have a granular fracture. On remelting they become
somewhat richer in lead, through a tendency to liquation. They do not
oxidize in moist air, nor at their melting points. They are attacked in
the cold by hydrochloric and by strong sulphuric acid, with evolution
of hydrogen, and by strong nitric acid when hot; strong solution of
potassium hydroxide also attacks them. They are without action on
distilled water, whether cold or hot.
«Zinc.»—Well-defined alloys were obtained, corresponding to the
formulas Zn_〈3〉Al, Zn_〈2〉Al, ZnAl, ZnAl_〈2〉, ZnAl_〈3〉, ZnAl_〈4〉,
ZnAl_〈6〉, ZnAl_〈10〉, ZnAl_〈12〉. Their melting points and densities
all lie between those of zinc and aluminum, and those containing most
zinc are the hardest. They are all dissolved by cold hydrochloric acid
and by hot dilute nitric acid. Cold concentrated nitric acid attacks
the first three, and cold dilute acid the first five. The Zn_〈3〉Al,
ZnAl_〈6〉, ZnAl_〈10〉, and ZnAl_〈12〉 are only slightly affected by
cold potassium-hydroxide solution; the others are strongly attacked,
potassium zincate and aluminate probably being formed.
«Tin.»—A filed rod of tin-aluminum alloy plunged in cold water gives
off for some minutes bubbles of gas, composed of hydrogen and oxygen
in explosive proportions. An unfiled rod, or a filed rod of either
aluminum or tin, is without action, though the unfiled rod of alloy
will act on boiling water. The filed rod of alloy, in faintly acid
solution of copper or zinc sulphate, becomes covered with a deposit
of copper or zinc, while bubbles of oxygen are given off. M. Pecheux
believes that the metals are truly alloyed only at the surface, and
that filing lays bare an almost infinitely numerous series of junctions
of the two metals, which, heated by the filing, act as thermocouples.
«Bismuth.»—By the method used for lead, bismuth alloys were obtained
containing 75, 85, 88, and 94 per cent of aluminum, with densities
2.86, 2.79, 2.78, and 2.74 respectively. They were sonorous, brittle,
finely grained, and homogeneous, silver-white, and with melting points
between those of their constituents, but nearer that of aluminum. They
are not oxidized in air at the temperature of casting, but are readily
attacked by acids, concentrated or dilute, and by potassium-hydroxide
solution. The filed alloys behave like those of tin, but still more
markedly.
«Magnesium.»—These were obtained with 66, 68, 73, 77, and 85 per cent
of aluminum, and densities 2.24, 2.47, 2.32, 2.37, 2.47. They are
brittle, with large granular fracture, silver-white, file well, take
a good polish, and have melting points near that of aluminum. Being
viscous when melted, they are difficult to cast, and when slowly cooled
form a gray, spongy mass which cannot be remelted. They do not oxidize
in air at the ordinary temperatures, but burn readily at a bright-red
heat. They are attacked violently by acids and by potassium-hydroxide
solution, decompose hydrogen peroxide, and slowly decompose water even
in the cold.
«Tin, Bismuth, and Magnesium.»—The action of water on these alloys
just referred to has been recently demonstrated on a larger scale, 5
to 6 cubic centimeters of hydrogen having been obtained in 20 minutes
from 2 cubic centimeters of the filed tin alloy. The bismuth alloy
yielded more hydrogen than the tin alloy, and the magnesium alloy more
than the bismuth alloy. The oxygen of the decomposed water unites
with the aluminum. Larger quantities of hydrogen are obtained from
copper-sulphate solution, apart from the decomposition of this solution
by precipitation of copper at the expense of the metal alloyed with the
aluminum. The alloys of aluminum with zinc and lead do not decompose
pure water, but do decompose the water of copper-sulphate solution,
and, more slowly, that of zinc-sulphate solution.
Aluminum is a metal whose properties are very materially influenced
by a proportionately small addition of copper. Alloys of 99 per cent
aluminum and 1 per cent of copper are hard, brittle, and bluish in
color; 95 per cent of aluminum and 5 per cent of copper give an alloy
which can be hammered, but with 10 percent of copper the metal can no
longer be worked. With 80 per cent and upward of copper are obtained
alloys of a beautiful yellow color, and these mixtures, containing
from 5 to 10 percent of aluminum and from 90 to 95 per cent of copper,
are the genuine aluminum bronzes. The 10-per-cent alloys are of a pure
golden-yellow color; with 5 per cent of aluminum they are reddish
yellow, like gold heavily alloyed with copper, and a 2-per-cent
admixture is of an almost pure copper red. {50} As the proportion of
copper increases, the brittleness is diminished, and alloys containing
10 per cent and less of aluminum can be used for industrial purposes,
the best consisting of 90 per cent of copper and 10 of aluminum. The
hardness of this alloy approaches that of the general bronzes, whence
its name. It can be stretched out into thin sheets between rollers,
worked under the hammer, and shaped as desired by beating or pressure,
in powerful stamping presses. On account of its hardness it takes a
fine polish, and its peculiar greenish-gold color resembles that of
gold alloyed with copper and silver together.
Alloys with a still greater proportion of copper approach this metal
more and more nearly in their character; the color of an alloy, for
instance, composed of 95 per cent of copper and 5 per cent of aluminum,
can be distinguished from pure gold only by direct comparison, and the
metal is very hard, and also very malleable.
«Electrical Conductivity of Aluminum Alloys.»—During three years’
exposure to the atmosphere, copper-aluminum alloys in one test
gradually diminished in conductivity in proportion to the amount of
copper they contained. The nickel-copper aluminum alloys, which show
such remarkably increased tensile strength as compared with good
commercial aluminum, considerably diminished in total conductivity.
On the other hand, the manganese-copper aluminum alloys suffered
comparatively little diminution in total conductivity, and one of them
retained comparatively high tensile strength. It was thought that an
examination of the structure of these alloys by aid of microphotography
might throw some light on the great difference which exists between
some of their physical properties. For instance, a nickel-copper
aluminum alloy has 1.6 times the tensile strength of ordinary
commercial aluminum. Under a magnification of 800 diameters practically
no structure could be discovered. Considering the remarkable
crystalline structure exhibited by ordinary commercial aluminum near
the surface of an ingot, when allowed to solidify at an ordinary rate,
the want of structure in these alloys must be attributed to the process
of drawing down. The inference is that the great difference which
exists between their tensile strengths and other qualities is not due
to variation in structure.
«Colored Alloys of Aluminum.»—A purple scintillating composition is
produced by an alloyage of 78 parts of gold and 22 parts aluminum.
With platinum a gold-colored alloy is obtained; with palladium a
copper-colored one; and with cobalt and nickel one of a yellow color.
Easily fusible metals of the color of aluminum give white alloys. Metal
difficult of fusion, such as iridium, osmium, titanium, etc., appear in
abnormal tones of color through such alloyages.
«Aluminum-Brass.»—Aluminum, 1 per cent; specific gravity, 8.35; tensile
strength, 40. Aluminum, 3 per cent; specific gravity, 8.33; tensile
strength, 65. The last named is harder than the first.
«Aluminum-Copper.»—Minikin is principally aluminum with a small
percentage of copper and nickel. It is alloyed by mixing the aluminum
and copper, then adding the nickel. It resembles palladium and is very
strong.
«Aluminum-Silver.»—I.—Silver, 3 per cent; aluminum, 97 per cent. A
handsome color.
II.—A silver aluminum that is easily worked into various articles
contains about one-fourth silver and three-fourths of aluminum.
«Aluminum-Tin.»—Bourbon metal is composed of equal parts of aluminum
and tin; it solders readily.
«Aluminum-Tungsten.»—A new metal alloy consisting of aluminum and
tungsten is used of late in France in the construction of conveyances,
especially carriages, bicycles, and motor vehicles. The French call
it partinium; the composition of the new alloy varies according to
the purposes for which it is used. It is considerably cheaper than
aluminum, almost as light, and has a greater resistance. The strength
is stated at 32 to 37 kilograms per square millimeter.
«Aluminum-Zinc.»—Zinc, 3 per cent; aluminum, 97 per cent. Very ductile,
white, and harder than aluminum.
AMALGAMS: See Fusible Alloys.
«Anti-Friction Bearing or Babbitt Metals.»—These alloys are usually
supported by bearings of brass, into which it is poured after they have
been tinned, and heated and put together with an exact model of the
axle, or other working piece, plastic clay being previously applied,
in the usual manner, as a lute or outer mold. Soft gun metal is also
excellent, and is much used for bearings. They all become less heated
in working than the {51} harder metals, and less grease or oil is
consequently required when they are used.
I.—An anti-friction metal of excellent quality and one that has been
used with success is made as follows: 17 parts zinc; 1 part copper;
1 1/2 parts antimony; prepared in the following way: Melt the copper
in a small crucible, then add the antimony, and lastly the zinc, care
being taken not to burn the zinc. Burning can be prevented by allowing
the copper and antimony to cool slightly before adding the zinc. This
metal is preferably cast into the shape desired and is not used
as a lining metal because it requires too great a heat to pour. It
machines nicely and takes a fine polish on bearing surfaces. It has the
appearance of aluminum when finished. Use a lubricating oil made from
any good grade of machine oil to which 3 parts of kerosene have been
added.
II.—Copper, 6 parts; tin, 12 parts; lead, 150 parts; antimony, 30
parts; wrought iron, 1 part; cast iron, 1 part. For certain purposes
the composition is modified as follows: Copper, 16 parts; tin, 40
parts; lead, 120 parts; antimony, 24 parts; wrought iron, 1 part; cast
iron, 1 part. In both cases the wrought iron is cut up in small pieces,
and in this state it will melt readily in fused copper and cast iron.
After the mixture has been well stirred, the tin, lead, and antimony
are added; these are previously melted in separate crucibles, and when
mingled the whole mass is again stirred thoroughly. The product may
then be run into ingots, to be employed when needed. When run into the
molds the surface should be well skimmed, for in this state it oxidizes
rapidly. The proportions may be varied without materially affecting the
results.
III.—From tin, 16 to 20 parts; antimony, 2 parts; lead, 1 part; fused
together, and then blended with copper, 80 parts. Used where there is
much friction or high velocity.
IV.—Zinc, 6 parts; tin, 1 part; copper, 20 parts. Used when the metal
is exposed to violent shocks.
V.—Lead, 1 part; tin, 2 parts; zinc, 4 parts; copper, 68 parts. Used
when the metal is exposed to heat.
VI.—Tin, 48 to 50 parts; antimony, 5 parts; copper, 1 part.
VII.—(Fenton’s.) Tin, with some zinc, and a little copper.
VIII.—(Ordinary.) Tin, or hard pewter, with or without a small portion
of antimony or copper. Without the last it is apt to spread out under
the weight of heavy machinery. Used for the bearings of locomotives,
etc.
The following two compositions are for motor and dynamo shafts: 100
pounds tin; 10 pounds copper; 10 pounds antimony.
83 1/2 pounds tin; 8 1/4 pounds antimony; 8 1/4 pounds copper.
IX.—Lead, 75 parts; antimony, 23 parts; tin, 2 parts.
X.—Magnolia Metal.—This is composed of 40 parts of lead, 7 1/2 parts
of antimony, 2 1/2 of tin, 1/8 of bismuth, 1/8 of aluminum, and
1/4 of graphite. It is used as an anti-friction metal, and takes its
name from its manufacturer’s mark, a magnolia flower.
ARGENTAN: See German Silver, under this title.
«BELL METAL.»
The composition of bell metal varies considerably, as may be seen below:
I.—(Standard.) Copper, 78 parts; tin, 22 parts; fused together and
cast. The most sonorous of all the alloys of copper and tin. It is
easily fusible, and has a fine compact grain, and a vitreous conchoidal
and yellowish-red fracture. According to Klaproth, the finest-toned
Indian gongs have this composition.
II.—(Founder’s Standard.) Copper, 77 parts; tin, 21 parts; antimony, 2
parts. Slightly paler and inferior to No. I.
III.—Copper, 80 parts; tin, 20 parts. Very deep-toned and sonorous.
Used in China and India for the larger gongs, tam-tams, etc.
IV.—Copper, 78 to 80 parts; tin, 22 to 20 parts. Usual composition of
Chinese cymbals, tam-tams, etc.
V.—Copper, 75 (= 3) parts; tin, 25 (= 1) part. Somewhat brittle. In
fracture, semivitreous and bluish-red. Used for church and other large
bells.
VI.—Copper, 80 parts; tin, 10 1/4 parts; zinc, 5 1/2 parts; lead,
4 1/4 parts. English bell metal, according to Thomson. Inferior to
the last; the lead being apt to form isolated drops, to the injury of
the uniformity of the alloy.
VII.—Copper, 68 parts; tin, 32 parts. Brittle; fracture conchoidal
and ash-gray. Best proportions for house bells, hand bells, etc.; for
which, however, 2 of copper and 1 of tin is commonly substituted by the
founders.
VIII.—Copper, 72 parts; tin, 26 1/2 parts; iron, 1 1/2 parts. Used
by the Paris houses for the bells of small clocks.
IX.—Copper, 72 parts; tin, 26 parts; zinc, 2 parts. Used, like the
last, for very small bells.
X.—Copper, 70 parts; tin, 26 parts; {52} zinc, 2 parts. Used for the
bells of repeating watches.
XI.—Melt together copper, 100 parts; tin, 25 parts. After being cast
into the required object, it should be made red-hot, and then plunged
immediately into cold water in order to impart to it the requisite
degree of sonorousness. For cymbals and gongs.
XII.—Melt together copper, 80 parts; tin, 20 parts. When cold it has to
be hammered out with frequent annealing.
XIII.—Copper, 78 parts; tin, 22 parts; This is superior to the former,
and it can be rolled out. For tam-tams and gongs.
XIV.—Melt together copper, 72 parts; tin, 26 to 56 parts; iron 1/44
part. Used in making the bells of ornamental French clocks.
Castings in bell metal are all more or less brittle; and, when recent,
have a color varying from a dark ash-gray to grayish-white, which is
darkest in the more cuprous varieties, in which it turns somewhat on
the yellowish-red or bluish-red. The larger the proportion of copper
in the alloy, the deeper and graver the tone of the bells formed of
it. The addition of tin, iron, or zinc, causes them to give out their
tones sharper. Bismuth and lead are also often used to modify the tone,
which each metal affects differently. The addition of antimony and
bismuth is frequently made by the founder to give a more crystalline
grain to the alloy. All these conditions are, however, prejudicial
to the sonorousness of bells, and of very doubtful utility. Rapid
refrigeration increases the sonorousness of all these alloys. Hence
M. D’Arcet recommends that the “pieces” be heated to a cherry-red
after they are cast, and after having been suddenly plunged into cold
water, that they be submitted to well-regulated pressure by skillful
hammering, until they assume their proper form; after which they are
to be again heated and allowed to cool slowly in the air. This is the
method adopted by the Chinese with their gongs, etc., a casing of sheet
iron being employed by them to support and protect the pieces during
the exposure to heat. In a general way, however, bells are formed and
completed by simple casting. This is necessarily the case with all
very large bells. Where the quality of their tones is the chief object
sought after, the greatest care should be taken to use commercially
pure copper. The presence of a very little lead or any similar metal
greatly lessens the sonorousness of this alloy; while that of silver
increases it.
The specific gravity of a large bell is seldom uniform through its
whole substance; nor can the specific gravity from any given portion
of its constituent metals be exactly calculated owing to the many
interfering circumstances. The nearer this uniformity is approached,
or, in other words, chemical combination is complete, the more durable
and finer-toned will be the bell. In general, it is found necessary to
take about one-tenth more metal than the weight of the intended bell,
or bells, in order to allow for waste and scorification during the
operations of fusing and casting.
«BISMUTH ALLOYS.»
Bismuth possesses the unusual quality of expanding in cooling. It is,
therefore, introduced in many alloys to reduce or check shrinkage in
the mold.
For delicate castings, and for taking impressions from dies, medals,
etc., various bismuth alloys are in use, whose composition corresponds
to the following figures:
I II III IV
Bismuth 6 5 2 8
Tin 3 2 1 3
Lead 13 3 1 5
V.—Cliché Metal.—This alloy is composed of tin, 48 parts; lead,
32.5; bismuth, 9; and antimony, 10.5. It is especially well adapted
to dabbing rollers for printing cotton goods, and as it possesses a
considerable degree of hardness, it wears well.
VI.—For filling out defective places in metallic castings, an alloy of
bismuth 1 part, antimony 3, lead 8, can be advantageously used.