polished, so closely resembles genuine gold in color that it can
scarcely be distinguished from it. Besides its beautiful color, it
has the valuable properties of being very ductile and tenacious, so
that it can easily be stamped into any desired shape; it also takes
a high polish. It is frequently used for the manufacture of spoons,
forks, etc., but is unsuitable for this purpose on account of the large
amount of copper contained in it, rendering it injurious to health. The
directions for preparing this alloy vary greatly. The products of some
Paris factories show the following composition:
I II III
Copper 90 80.5 86.21
Zinc 10 14.5 31.52
Tin — — 0.48
Iron — — 0.24
A special receipt for oreïde is the following:
IV.—Melt 100 parts of copper and add, with constant stirring, 6 parts
of magnesia, 3.6 of sal ammoniac, 1.8 of lime, and 9 of crude tartar.
Stir again {69} thoroughly, and add 17 parts of granulated zinc, and
after mixing it with the copper by vigorous stirring keep the alloy
liquid for one hour. Then carefully remove the scum and pour off the
alloy.
«Pinchbeck.»—This was first manufactured in England. Its dark gold
color is the best imitation of gold alloyed with copper. Being very
ductile, it can easily be rolled out into thin plates, which can be
given any desired shape by stamping. It does not readily oxidize, and
thus fulfills all the requirements for making cheap jewelry, which is
its principal use.
Copper 88.8 93.6
Zinc 11.2 6.4
Or
Copper 2.1 1.28
Zinc — 0.7
Brass 1.0 0.7
«Palladium Gold.»—Alloys of gold, copper, silver, and palladium have a
brownish-red color and are nearly as hard as iron. They are sometimes
(although rarely) used for the bearings for the axles of the wheels of
fine watches, as they invite little friction and do not rust in the
air. The composition used in the Swiss and English watch factories
consists usually of gold 18 parts, copper 13 parts, silver 11, and
palladium 6.
«Talmi Gold.»—The name of talmi gold was first applied to articles
of jewelry, chains, earrings, bracelets, etc., brought from Paris,
and distinguished by beautiful workmanship, a low price, and great
durability. Later, when this alloy had acquired a considerable
reputation, articles were introduced under the same name, but which
were really made of other metals, and which retained their beautiful
gold color only as long as they were not used. The fine varieties of
talmi gold are manufactured from brass, copper, or tombac, covered with
a thin plate of gold, combined with the base by rolling, under strong
pressure. The plates are then rolled out by passing through rollers,
and the coating not only acquires considerable density, but adheres so
closely to the base that the metal will keep its beautiful appearance
for years. Of late, many articles of talmi gold have been introduced
whose gold coating is produced by electroplating, and is in many cases
so thin that hard rubbing will bring through the color of the base.
Such articles, of course, are not durable. In genuine talmi gold, the
coating, even though it may be thin, adheres very closely to the base,
for the reason that the two metals are actually welded by the rolling,
and also because alloyed gold is always used, which is much harder
than pure gold. The pure gold of electroplating is very soft. The
composition of some varieties of talmi gold are here given. It will be
seen that the content of gold varies greatly, and the durability of the
alloy will, of course, correspond to this. The alloys I, II, III are
genuine Paris talmi gold; IV, V, and VI are electroplated imitations;
and VII is an alloy of a wrong composition, to which the gold does not
adhere firmly:
Copper Zinc Tin Iron Gold
I. 89.9 9.3 — — 1.3
II. 90.8 8.3 — — 0.9
III. 90.0 8.9 — — 0.9
IV. 90.7 89.0 — — 0.5
88.2 11.4
V. 87.5 12.4 — — 0.3
83.1 17.0
VI. 93.5 6.6 — — 0.05
84.5 15.8
VII. 86.0 12.0 1.1 0.3 —
«Japanese Alloys.»—In Japan some specialties in metallic alloys are in
use of which the composition is as follows:
Shadke consists of copper with from 1 to 10 per cent of gold. Articles
made from this alloy are laid in a pickle of blue vitriol, alum, and
verdigris, until they acquire a bluish-black color.
Gui-shi-bu-ichi is an alloy of copper containing 30 to 50 per cent of
silver. It possesses a peculiar gray shade.
Mokume consists of several compositions. Thus, about 30 gold foils
(genuine) are welded together with shadke, copper, silver, and
gui-shi-bu-ichi and pierced. The pierced holes are, after firmly
hammering together the plates, filled up with the above-named pickle.
The finest Japanese brass consists of 10 parts copper and 8 parts zinc,
and is called siachu. The bell metal kara kane is composed of copper 10
parts, tin 10 parts, iron 0.5 part, and zinc 1.5 parts. The copper is
first fused, then the remaining metals are added in rotation.
«GERMAN SILVER OR ARGENTAN.»
The composition of this alloy varies considerably, but from the
adjoined figures an average may be found, which will represent,
approximately, the normal composition:
Copper 50 to 66 parts
Zinc 19 to 31 parts
Nickel 13 to 18 parts
The properties of the different kinds, such as their color, ductility,
fusibility, {70} etc., vary with the proportions of the single metals.
For making spoons, forks, cups, candlesticks, etc., the most suitable
proportions are 50 parts of copper, 25 of zinc, and 25 of nickel. This
metal has a beautiful blue-white color, and does not tarnish easily.
German silver is sometimes so brittle that a spoon, if allowed to
fall upon the floor, will break; this, of course, indicates faulty
composition. But the following table will show how the character of the
alloy changes with the varying percentage of the metals composing it:
Copper Zinc Nickel Quality
I. 8 3.5 4 Finest quality.
II. 8 3.5 6 Beautiful, but refractory.
III. 8 6.5 3 Ordinary, readily fusible.
IV. 52 26.0 22 First quality.
V. 59 30.0 11 Second quality.
VI. 63 31.0 6 Third quality.
The following analyses give further particulars in regard to different
kinds of German silver:
───────────+──────+──────+──────+─────+──────
For sheet │Copper│ Zinc │Nickel│ Lead│ Iron
───────────+──────+──────+──────+─────+──────
(French) │ 50.0 │ 31.3 │ 18.7 │ — │ —
(French) │ 50.0 │ 30.0 │ 20.0 │ — │ —
(French) │ 58.3 │ 25.0 │ 16.7 │ — │ —
Vienna │ 50.0 │ 25.0 │ 25.0 │ — │ —
Vienna │ 55.6 │ 22.0 │ 22.0 │ — │ —
Vienna │ 60.0 │ 20.0 │ 20.0 │ — │ —
Berlin │ 54.0 │ 28.0 │ 18.0 │ — │ —
Berlin │ 55.5 │ 29.1 │ 17.5 │ — │ —
English │ 63.34│ 17.01│ 19.13│ — │ —
English │ 62.40│ 22.15│ 15.05│ — │ —
English │ 62.63│ 26.05│ 10.85│ — │ —
English │ 57.40│ 25. │ 13.0 │ — │ 3.0
Chinese │ 26.3 │ 36.8 │ 36.8 │ — │ —
Chinese │ 43.8 │ 40.6 │ 15.6 │ — │ —
Chinese │ 45.7 │ 36.9 │ 17.9 │ — │ —
Chinese │ 40.4 │ 25.4 │ 31.6 │ — │ 2.6
Castings │ 48.5 │ 24.3 │ 24.3 │ 2.9 │ —
Castings │ 54.5 │ 21.8 │ 21.8 │ 1.9 │ —
Castings │ 58.3 │ 19.4 │ 19.4 │ 2.9 │ —
Castings │ 57.8 │ 27.1 │ 14.3 │ 0.8 │ —
Castings │ 57. │ 20.0 │ 20.0 │ 3.0 │ —
───────────+──────+──────+──────+─────+──────
In some kinds of German silver are found varying quantities of iron,
manganese, tin, and very frequently lead, added for the purpose
of changing the properties of the alloy or cheapening the cost of
production. But all these metals have a detrimental rather than
a beneficial effect upon the general character of the alloy, and
especially lessen its power of resistance to the action of dilute
acids, one of its most valuable properties. Lead makes it more fusible;
tin acts somewhat as in bronze, making it denser and more resonant, and
enabling it to take a higher polish. With iron or manganese the alloy
is whiter, but it becomes at the same time more refractory and its
tendency toward brittleness is increased.
«SUBSTITUTES FOR GERMAN SILVER.»
There are many formulas for alloys which claim to be substitutes for
German silver; but no one of them has yet become an article of general
commerce. It will be sufficient to note these materials briefly, giving
the composition of the most important.
«Nickel Bronze.»—This is prepared by fusing together very highly
purified nickel (99.5 per cent) with copper, tin, and zinc. A bronze is
produced containing 20 per cent of nickel, light-colored and very hard.
«Bismuth Bronze.»—
I II III IV
Copper 25.0 45.0 69.0 47.0
Nickel 24.0 32.5 10.0 30.9
Antimony 50.0 — — —
Bismuth 1.0 1.0 1.0 0.1
Tin — 16.0 15.0 1.0
Zinc — 21.5 20.0 21.0
Aluminum — — 1.0 —
I is hard and very lustrous, suitable for lamp reflectors and axle
bearings; II is hard, resonant, and not affected by sea water, for
parts of ships, pipes, telegraph wires, and piano strings; III and IV
are for cups, spoons, etc.
«Manganese Argentan.»—
Copper 52 to 50 parts
Nickel 17 to 15 parts
Zinc 5 to 10 parts
Manganese 1 to 5 parts
Copper, with 15 per
cent phosphorus. 3 to 5 parts
Readily cast for objects of art.
«Aphtite.»—
Iron 66 parts
Nickel 23 parts
Tungsten 4 parts
Copper 5 parts
«Arguzoid.»—
Copper 55.78 parts
Zinc 23.198 parts
Nickel 13.406 parts
Tin 4.035 parts
Lead 3.544 parts
Silver white, almost ductile, suited for artistic purposes. {71}
«Ferro-Argentan.»—
Copper 70.0 parts
Nickel 20.0 parts
Zinc 5.5 parts
Cadmium 4.5 parts
Resembles silver; worked like German silver.
«Silver Bronze.»—Manganese, 18 per cent; aluminum, 1.2 per cent;
silicium, 5 per cent; zinc, 13 per cent; copper, 67.5 per cent. The
electric resistance of silver bronze is greater than that of German
silver, hence it ought to be highly suitable for rheostats.
«Instrument Alloys.»—The following are suitable for physical and
optical instruments, metallic mirrors, telescopes, etc.:
I.—Copper, 62 parts; tin, 33 parts; lead, 5 parts.
II.—Copper, 80; antimony, 11; lead, 9.
III.—Copper, 10; tin, 10; antimony, 10; lead, 40.
IV.—Copper, 30; tin, 50; silver, 2; arsenic, 1.
V.—Copper, 66; tin, 33.
VI.—Copper, 64; tin, 26.
VII.—Steel, 90; nickel, 10.
VIII.—Platinum, 60; copper, 40.
IX.—Platinum, 45; steel, 55.
X.—Platinum, 55; iron, 45.
XI.—Platinum, 15; steel, 85.
XII.—Platinum, 20; copper, 79; arsenic, 1.
XIII.—Platinum, 62; iron, 28; gold, 10.
XIV.—Gold, 48; zinc, 52.
XV.—Steel, 50; rhodium, 50.
XVI.—Platinum, 12; iridium, 88.
XVII.—Copper, 89.5; tin, 8.5; zinc, 2.
«LEAD ALLOYS.»
The following alloys, principally lead, are used for various purposes:
«Bibra Alloy.»—This contains 8 parts of bismuth, 9 of tin, and 38 to 40
of lead.
«Metallic Coffins.»—Tin, 40 parts; lead, 45 parts; copper, 15 parts.
«Plates for Engraving.»—I.—Lead, 84 parts; antimony, 16 parts.
II.—Lead, 86 parts; antimony, 14 parts.
III.—Lead, 87 parts; antimony, 12 parts; copper, 1 part.
IV.—Lead, 81 parts; antimony, 14 parts; tin, 5 parts.
V.—Lead, 73 parts; antimony, 17 parts; zinc, 10 parts.
VI.—Tin, 53 parts; lead, 43 parts; antimony, 4 parts.
Hard lead is made of lead, 84 parts; antimony, 16 parts.
«Sheet Metal Alloy.»—
Tin 35 parts
Lead 250 parts
Copper 2.5 parts
Zinc 0.5 part
This alloy has a fine white color, and can be readily rolled into thin
sheets. For that reason it is well adapted for lining tea chests
and for the production of tobacco and chocolate wrappers. The copper
and zinc are used in the form of fine shavings. The alloy should be
immediately cast into thin plates, which can then be passed through
rolls.
«MAGNETIC ALLOYS.»
Alloys which can be magnetized most strongly are composed of copper,
manganese, and aluminum, the quantities of manganese and aluminum being
proportional to their atomic weights (55.0 to 27.1, or about 2 to 1).
The maximum magnetization increases rapidly with increase of manganese,
but alloys containing much manganese are exceedingly brittle and cannot
be wrought. The highest practicable proportion of manganese at present
is 24 per cent.
These magnetic alloys were studied by Hensler, Haupt, and Starck, and
Gumlich has recently examined them at the Physikalisch—technische
Reichsanstalt, with very remarkable and interesting results.
The two alloys examined were composed as follows:
Alloy I.—Copper, 61.5 per cent; manganese, 23.5 per cent; aluminum, 15
per cent; lead, 0.1 per cent, with traces of iron and silicon.
Alloy II.—Copper, 67.7 per cent; manganese, 20.5 per cent; aluminum,
10.7 per cent; lead, 1.2 per cent, with traces of iron and silicon.
Alloy II could be worked without difficulty, but alloy I was so
brittle that it broke under the hammer. A bar 7 inches long and 1/4
inch thick was obtained by grinding. This broke in two during the
measurements, but, fortunately, without invalidating them. Such a
material is evidently unsuited to practical uses.
The behavior of magnetic alloys at high temperatures is very peculiar.
Alloy I is indifferent to temperature changes, which scarcely affect
its magnetic properties, but the behavior of alloy II is very
different. Prolonged heating to 230° F. produces a great increase in
its capability of magnetization, which, after 544 hours’ heating, rises
from 1.9 to 3.2 kilogauss, {72} approaching the strength of alloy I.
But when alloy II is heated to 329° F., its capability of magnetization
fails again and the material suffers permanent injury, which can be
partly, but not wholly, cured by prolonged heating.
Another singular phenomenon was exhibited by both of these alloys. When
a bar of iron is magnetized by an electric current, it acquires its
full magnetic strength almost instantaneously on the closure of the
circuit. The magnetic alloys, on the contrary, do not attain their full
magnetization for several minutes. In some of the experiments a gradual
increase was observed even after the current had been flowing five
minutes.
In magnetic strength alloy I proved far superior to alloy II, which
contained smaller proportions of manganese and aluminum. Alloy I showed
magnetic strengths up to 4.5 kilogauss, while the highest magnetization
obtained with alloy II was only 1.9 kilogauss. But even alloy II may
be called strongly magnetic, for its maximum magnetization is about
one-tenth that of good wrought iron (18 to 20 kilogauss), or one-sixth
that of cast iron (10 to 12 kilogauss). Alloy I is nearly equal in
magnetic properties to nickel, which can be magnetized up to about 5
kilogauss.
«MANGANESE ALLOYS:»
«Manganese bronze» is a bronze deprived of its oxide by an admixture of
manganese. The manganese is used as copper manganese containing 10 to
30 per cent manganese and added to the bronze to the amount of 0.5 to 2
per cent.
«Manganese Copper.»—The alloys of copper with manganese have a
beautiful silvery color, considerable ductility, great hardness and
tenacity, and are more readily fusible than ordinary bronze. A special
characteristic is that they exactly fill out the molds, without the
formation of blowholes, and present no difficulties in casting.
Cupromanganese is suitable for many purposes for which nothing else but
bronze can advantageously be used, and the cost of its production is no
greater than that of genuine bronze. In preparing the alloy, the copper
is used in the form of fine grains, obtained by pouring melted copper
into cold water. These copper grains are mixed with the dry oxide of
manganese, and the mixture put into a crucible holding about 66 pounds.
Enough space must be left in the crucible to allow a thick cover of
charcoal, as the manganese oxidizes easily. The crucible is placed in
a well-drawing wind furnace and subjected to a strong white heat. The
oxide of manganese is completely reduced to manganese, which at once
combines with the copper to form an alloy. In order to prevent, as far
as possible, the access of air to the fusing mass, it is advisable to
cover the crucible with a lid which has an aperture in the center for
the escape of the carbonic oxide formed during the reduction.
When the reduction is complete and the metals fused, the lid is removed
and the contents of the crucible stirred with an iron rod, in order
to make the alloy as homogeneous as possible. By repeated remelting
of the cupromanganese a considerable quantity of the manganese is
reconverted into oxide; it is, therefore, advisable to make the
casts directly from the crucible. When poured out, the alloy rapidly
solidifies, and resembles in appearance good German silver. Another
reason for avoiding remelting is that the crucible is strongly attacked
by the cupromanganese, and can be used but a few times.
The best kinds of cupromanganese contain between 10 and 30 per cent
of manganese. They have a beautiful white color, are hard, tougher
than copper, and can be worked under the hammer or with rolls. Some
varieties of cupromanganese which are especially valuable for technical
purposes are given below:
I II III IV
Copper 75 60 65 60
Manganese 25 25 20 20
Zinc — 15 5 —
Tin — — — 10
Nickel — — 10 10
«Manganin.»—This is an alloy of copper, nickel, and manganese for
electric resistances.
«MIRROR ALLOYS:»
«Amalgams for Mirrors.»—I.—Tin, 70 parts; mercury, 30 parts.
II.—For curved mirrors. Tin, 1 part; lead, 1 part; bismuth, 1 part;
mercury, 9 parts.
III.—For glass balls. Tin, 80 parts; mercury, 20 parts.
IV.—Metallic cement. Copper, 30 parts; mercury, 70 parts.
V.—Mirror metal.—Copper, 100 parts; tin, 50 parts; Chinese copper, 8
parts; lead, 1 part; antimony, 1 part.
«Reflector Metals.»—I.—(Cooper’s.) Copper, 35 parts; platinum, 6;
zinc, 2; tin, 16.5; arsenic, 1. On account of the hardness of this
alloy, it takes a very high polish; it is impervious to the effects
of the weather, and is therefore remarkably {73} well adapted to the
manufacture of mirrors for fine optical instruments.
II.—(Duppler’s.) Zinc, 20 parts; silver, 80 parts.
III.—Copper, 66.22 parts; tin, 33.11 parts; arsenic, 0.67 part.
IV.—Copper, 64 parts; tin, 32 parts; arsenic, 4 parts.
V.—Copper, 82.18 parts; lead, 9.22 parts; antimony, 8.60 parts.
VI.—(Little’s.) Copper, 69.01 parts; tin, 30.82 parts; zinc, 2.44
parts; arsenic, 1.83 parts.
«Speculum Metal.»—Alloys consisting of 2 parts of copper and 1 of tin
can be very brilliantly polished, and will serve for mirrors. Good
speculum metal should have a very fine-grained fracture, should be
white and very hard, the highest degree of polish depending upon these
qualities. A composition to meet these requirements must contain at
least 35 to 36 per cent of copper. Attempts have frequently been made
to increase the hardness of speculum metal by additions of nickel,
antimony, and arsenic. With the exception of nickel, these substances
have the effect of causing the metal to lose its high luster easily,
any considerable quantity of arsenic in particular having this effect.
The real speculum metal seems to be a combination of the formula
Cu_〈4〉Sn, composed of copper 68.21 per cent, tin 31.7. An alloy of
this nature is sometimes separated from ordnance bronze by incorrect
treatment, causing the so-called tin spots; but this has not the pure
white color which distinguishes the speculum metal containing 31.5
per cent of tin. By increasing the percentage of copper the color
gradually shades into yellow; with a larger amount of tin into blue. It
is dangerous to increase the tin too much, as this changes the other
properties of the alloy, and it becomes too brittle to be worked.
Below is a table showing different compositions of speculum metal. The
standard alloy is undoubtedly the best.
Copper Tin Zinc Arsenic Silver
Standard alloy 68.21 31.7 — — —
Otto’s alloy 68.5 31.5 — — —
Richardson’s alloy 65.3 30.0 0.7 2. 2.
Sollit’s alloy 64.6 31.3 4.1 Nickel —
Chinese speculum metal 80.83 — — 8.5 Antimony
Old Roman 63.39 19.05 — 17.29 Lead
«PALLADIUM ALLOYS.»
I.—An alloy of palladium 24 parts, gold 80, is white, hard as steel,
unchangeable in the air, and can, like the other alloys of palladium,
be used for dental purposes.
II.—Palladium 6 parts, gold 18, silver 11, and copper 13, gives a
reddish-brown, hard, and very fine-grained alloy, suitable for the
bearings of pivots in clock works.
The alloys of most of the other platinum metals, so called, are little
used on account of their rarity and costliness. Iridium and rhodium
give great hardness to steel, but the commercial rhodium and iridium
steel, so called, frequently contains not a trace of either. The
alloy of iridium with osmium has great hardness and resistance and is
recommended for pivots, fine instruments, and points of ship compasses.
«Palladium Silver.»—This alloy, composed of 9 parts of palladium and 1
of silver, is used almost exclusively for dental purposes, and is well
suited to the manufacture of artificial teeth, as it does not oxidize.
An alloy even more frequently used than this consists of platinum 10
parts, palladium 8, and gold 6.
«Palladium Bearing Metal.»—This alloy is extremely hard, and is used
instead of jewel bearings in watches. It is composed of palladium 24
parts, gold 72, silver 44, copper 92.
«PLATINUM ALLOYS.»
Platinum has usually been alloyed with silver in goldsmith’s work,
2 parts silver to 1 of platinum being taken to form the favorite
“platinum silver.” The object has been to produce an alloy having a
white appearance, which can be polished, and at the same time has a low
melting point. In addition to this platinum alloy the following are
well known:
I.—A mixture of 7 parts platinum with 3 parts iridium. This gives to
platinum the hardness of steel, which can be still further increased by
taking 4 parts of iridium.
II.—An alloy of 9 parts platinum and 1 part iridium is used by the
French in the manufacture of measuring instruments of great resisting
power.
Compounds of copper, nickel, cadmium, and tungsten are also used in
the construction of parts of watches; the latter acquire considerable
hardness without becoming magnetic or rusting like steel.
III.—For this purpose a compound of {74} 62.75 parts platinum, 18 parts
copper, 1.25 parts cadmium, and 18 parts nickel is much recommended.
IV.—Very ductile platinum-copper alloys have also been made, e. g.,
the so-called Cooper gold, consisting of 3 parts platinum and 13 parts
copper, which is almost equal to 18-carat gold in regard to color,
finish, and ductility. If 4 per cent of platinum is taken, these
latter alloys acquire a rose-red color, while a golden-yellow color
can be produced by further adding from 1 to 2 per cent (in all 5 to 6
per cent) of platinum. The last-named alloy is extensively used for
ornaments, likewise alloy V.
V.—Ten parts platinum, 60 parts nickel, and 220 parts brass, or 2 parts
platinum, 1 part nickel and silver respectively, 2 parts brass, and 5
parts copper; this also gives a golden-yellow color.
VI.—For table utensils a favorite alloy is composed of 1 part platinum,
100 parts nickel, and 10 parts tin. Articles made of the latter alloy
are impervious to atmospheric action and keep their polish for a long
time. Pure white platinum alloys have for some time been used in dental
work, and they have also proved serviceable for jewelry.
VII.—A mixture of 30 parts platinum, 10 parts gold, and 3 parts silver,
or 7 parts platinum, 2 parts gold, and 3 parts silver.
VIII.—For enameled articles: Platinum, 35 parts; silver, 65 parts.
First fuse the silver, then add the platinum in the spongy form. A good
solder for this is platinum 80 parts, copper 20 parts.
IX.—For pens: Platinum, 4 parts; silver, 3 parts; copper, 1 part.
«Platinum Gold.»—Small quantities of platinum change the
characteristics of gold in many respects. With a small percentage the
color is noticeably lighter than that of pure gold, and the alloys are
extremely elastic; alloys containing more than 20 per cent of platinum,
however, almost entirely lose their elasticity. The melting point of
the platinum-gold alloy is high, and alloys containing 70 per cent
of platinum can be fused only in the flame of oxyhydrogen gas, like
platinum itself. Alloys with a smaller percentage of platinum can be
prepared in furnaces, but require the strongest white heat. In order
to avoid the chance of an imperfect alloy from too low a temperature,
it is always safer to fuse them with the oxyhydrogen flame. The alloys
of platinum and gold have a somewhat limited application. Those which
contain from 5 to 10 per cent of platinum are used for sheet and wire
in the manufacture of artificial teeth.
«Platinum-Gold Alloys for Dental Purposes.»—
I II III
Platinum 6 14 10
Gold 2 4 6
Silver 1 6 —
Palladium — — 8
«Platinum Silver.»—An addition of platinum to silver makes it harder,
but also more brittle, and changes the white color to gray. An alloy
which contains only a very small percentage of platinum is noticeably
darker in color than pure silver. Such alloys are prepared under the
name of _platine au titre_, containing between 17 and 35 per cent of
platinum. They are almost exclusively used for dental purposes.
«Imitation Platinum.»—I.—Brass, 100 parts; zinc, 65 parts.