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= Bismuth =
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Introduction
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Bismuth is a chemical element; it has symbol Bi and atomic number 83.
It is a post-transition metal and one of the pnictogens, with chemical
properties resembling its lighter group 15 siblings arsenic and
antimony. Elemental bismuth occurs naturally, and its sulfide and
oxide forms are important commercial ores. The free element is 86% as
dense as lead. It is a brittle metal with a silvery-white color when
freshly produced. Surface oxidation generally gives samples of the
metal a somewhat rosy cast. Further oxidation under heat can give
bismuth a vividly iridescent appearance due to thin-film interference.
Bismuth is both the most diamagnetic element and one of the least
thermally conductive metals known.
Bismuth was formerly understood to be the element with the highest
atomic mass whose nuclei do not spontaneously decay. However, in 2003
it was found to be very slightly radioactive. The metal's only
primordial isotope, bismuth-209, undergoes alpha decay with a
half-life roughly a billion times longer than the estimated age of the
universe.
Bismuth metal has been known since ancient times. Before modern
analytical methods bismuth's metallurgical similarities to lead and
tin often led it to be confused with those metals. The etymology of
"bismuth" is uncertain. The name may come from mid-sixteenth century
Neo-Latin translations of the German words or , meaning 'white mass',
which were rendered as or .
Bismuth compounds account for about half the global production of
bismuth. They are used in cosmetics; pigments; and a few
pharmaceuticals, notably bismuth subsalicylate, used to treat
diarrhea. Bismuth's unusual propensity to expand as it solidifies is
responsible for some of its uses, as in the casting of printing type.
Bismuth, when in its elemental form, has unusually low toxicity for a
heavy metal. As the toxicity of lead and the cost of its environmental
remediation became more apparent during the 20th century, suitable
bismuth alloys have gained popularity as replacements for lead.
Presently, around a third of global bismuth production is dedicated to
needs formerly met by lead.
History and etymology
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Bismuth metal has been known since ancient times and it was one of the
first 10 metals to have been discovered. The name 'bismuth' dates to
around 1665 and is of uncertain etymology. The name possibly comes
from obsolete German ', ', ' (early 16th century), perhaps related to
Old High German ' ("white"). The Neo-Latin ' (coined by Georgius
Agricola, who Latinized many German mining and technical words) is
from the German ', itself perhaps from ', meaning "white mass".
The element was confused in early times with tin and lead because of
its resemblance to those elements. Because bismuth has been known
since ancient times, no one person is credited with its discovery.
Agricola (1546) states that bismuth is a distinct metal in a family of
metals including tin and lead. This was based on observation of the
metals and their physical properties.
Miners in the age of alchemy also gave bismuth the name ',' or "silver
being made" in the sense of silver still in the process of being
formed within the Earth.
Bismuth was also known to the Incas and used (along with the usual
copper and tin) in a special bronze alloy for knives.
Beginning with Johann Heinrich Pott in 1738, Carl Wilhelm Scheele, and
Torbern Olof Bergman, the distinctness of lead and bismuth became
clear, and Claude François Geoffroy demonstrated in 1753 that this
metal is distinct from lead and tin.
Physical characteristics
==========================
Bismuth is a brittle metal with a dark, silver-pink hue, often with an
iridescent oxide tarnish showing many colors from yellow to blue. The
spiral, stair-stepped structure of bismuth crystals is the result of a
higher growth rate around the outside edges than on the inside edges.
The variations in the thickness of the oxide layer that forms on the
surface of the crystal cause different wavelengths of light to
interfere upon reflection, thus displaying a rainbow of colors. When
burned in oxygen, bismuth burns with a blue flame and its oxide forms
yellow fumes. Its toxicity is much lower than that of its neighbors in
the periodic table, such as lead and antimony.
No other metal is verified to be more naturally diamagnetic than
bismuth. (Superdiamagnetism is a different physical phenomenon.) Of
any metal, it has one of the lowest values of thermal conductivity
(after manganese, neptunium and plutonium) and the highest Hall
coefficient. It has a high electrical resistivity. When deposited in
sufficiently thin layers on a substrate, bismuth is a semiconductor,
despite being a post-transition metal. Elemental bismuth is denser in
the liquid phase than the solid, a characteristic it shares with
germanium, silicon, gallium, and water. Bismuth expands 3.32% on
solidification; therefore, it was long a component of low-melting
typesetting alloys, where it compensated for the contraction of the
other alloying components to form almost isostatic bismuth-lead
eutectic alloys.
Though virtually unseen in nature, high-purity bismuth can form
distinctive, colorful hopper crystals. It is relatively nontoxic and
has a low melting point just above 271 C, so crystals may be grown
using a household stove, although the resulting crystals will tend to
be of lower quality than lab-grown crystals.
At ambient conditions, bismuth shares the same layered structure as
the metallic forms of arsenic and antimony, crystallizing in the
rhombohedral lattice. When compressed at room temperature, this Bi-I
structure changes first to the monoclinic Bi-II at 2.55 GPa, then to
the tetragonal Bi-III at 2.7 GPa, and finally to the body-centered
cubic Bi-V at 7.7 GPa. The corresponding transitions can be monitored
via changes in electrical conductivity; they are rather reproducible
and abrupt and are therefore used for calibration of high-pressure
equipment.
Chemical characteristics
==========================
Bismuth is stable to both dry and moist air at ordinary temperatures.
When red-hot, it reacts with water to make bismuth(III) oxide.
:
It reacts with fluorine to form bismuth(V) fluoride at 500 C or
bismuth(III) fluoride at lower temperatures (typically from Bi melts);
with other halogens it yields only bismuth(III) halides. The
trihalides are corrosive and easily react with moisture, forming
oxyhalides with the formula BiOX.
: (X = F, Cl, Br, I)
:
Bismuth dissolves in concentrated sulfuric acid to make bismuth(III)
sulfate and sulfur dioxide.
:
It reacts with nitric acid to make bismuth(III) nitrate (which
decomposes into nitrogen dioxide when heated).
:
It also dissolves in hydrochloric acid, but only with oxygen present.
:
Isotopes
==========
The only primordial isotope of bismuth, bismuth-209, was regarded as
the heaviest stable nuclide, but it had long been suspected to be
unstable on theoretical grounds. This was finally demonstrated in
2003, when researchers at the 'Institut d'astrophysique spatiale' in
Orsay, France, measured the alpha (α) decay half-life of (209)Bi to be
(3 Bq/Mg), over times longer than the estimated age of the universe.
Due to its hugely long half-life, for all known medical and industrial
applications, bismuth can be treated as stable. The radioactivity is
of academic interest because bismuth is one of a few elements whose
radioactivity was suspected and theoretically predicted before being
detected in the laboratory. Bismuth has the longest known α-decay
half-life, though tellurium-128 has a double beta decay half-life of
over .
Six isotopes of bismuth with short half-lives (210-215 inclusive)
occur in the natural radioactive decay chains of actinium, radium,
thorium, and neptunium; and more have been synthesized. (Though all
primordial (237)Np has long since decayed, it is continually
regenerated by (n,2n) knockout reactions on natural (238)U.)
Commercially, bismuth-213 can be produced by bombarding radium with
bremsstrahlung photons from a linear particle accelerator. In 1997, an
antibody conjugate with bismuth-213, which has a 45-minute half-life
and α-decays, was used to treat leukemia patients. This isotope has
also been tried in cancer treatment, for example, in the targeted
alpha therapy (TAT) program.
Chemical compounds
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Chemically, bismuth resembles arsenic and antimony, but is much less
toxic. In almost all known compounds, bismuth has oxidation state +3;
a few have states +5 or −3.
The trioxide and trisulfide can both be made from the elements,
although the trioxide is extremely corrosive at high temperatures. The
pentoxide is not stable at room temperature, and will evolve oxygen
gas if heated. Both oxides form complex anions, and NaBiO3 is a strong
oxidising agent. The trisulfide is common in bismuth ore.
Similarly, bismuth forms all possible trihalides, but the only
pentahalide is BiF5. All are Lewis acids. Bismuth forms several
formally-BiI halides; these are complex salts with
unusually-structured polyatomic cations and anions.
In strongly acidic aqueous solution, the Bi ion solvates to form . As
pH increases, the cations polymerize until the octahedral bismuthyl
complex , often abbreviated BiO+. Although bismuth oxychloride and
bismuth oxynitrate have stoichiometries suggesting the ion, they are
double salts instead. Bismuth nitrate (not 'oxy'nitrate) is one of the
few aqueous-insoluble nitrate salts.
Bismuth forms very few stable bismuthides, intermetallic compounds in
which it attains oxidation state −3. The hydride spontaneously
decomposes at room temperature and stabilizes only below −60 C. Sodium
bismuthide has interest as a topological Dirac insulator.
Occurrence and production
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The reported abundance of bismuth in the Earth's crust varies
significantly by source from 180ppb (similar to that of silver) to
8ppb (twice as common as gold). The most important ores of bismuth are
bismuthinite and bismite. Native bismuth is known from Australia,
Bolivia, and China.
World bismuth production, 2022, in tonnes
Country Refining
!China |16,000
!Laos |2,000
!South Korea |950
!Japan 480
!Kazakhstan |220
!Other |350
!Total |20,000
According to the United States Geological Survey (USGS), 10,200 tonnes
of bismuth were produced worldwide by mining and 17,100 tonnes by
refining in 2016. Since then, USGS does not provide mining data for
bismuth, considering them unreliable. Globally, bismuth is mostly
produced by refining, as a byproduct of extraction of other metals
such as lead, copper, tin, molybdenum and tungsten, though the
refining-to-mining ratio depends on the country.
Bismuth travels in crude lead bullion (which can contain up to 10%
bismuth) through several stages of refining, until it is removed by
the Kroll-Betterton process which separates the impurities as slag, or
the electrolytic Betts process. Bismuth will behave similarly with
another of its major metals, copper. The raw bismuth metal from both
processes contains still considerable amounts of other metals,
foremost lead. By reacting the molten mixture with chlorine gas the
metals are converted to their chlorides while bismuth remains
unchanged. Impurities can also be removed by various other methods for
example with fluxes and treatments yielding high-purity bismuth metal
(over 99% Bi).
Price
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The price for pure bismuth metal was relatively stable through most of
the 20th century, except for a spike in the 1970s. Bismuth has always
been produced mainly as a byproduct of lead refining, and thus the
price usually reflected the cost of recovery and the balance between
production and demand.
Before World War II, demand for bismuth was small and mainly
pharmaceutical--bismuth compounds were used to treat such conditions
as digestive disorders, sexually transmitted diseases and burns. Minor
amounts of bismuth metal were consumed in fusible alloys for fire
sprinkler systems and fuse wire. During World War II bismuth was
considered a strategic material, used for solders, fusible alloys,
medications and atomic research. To stabilize the market, the
producers set the price at $1.25 per pound ($2.75 /kg) during the war
and at $2.25 per pound ($4.96 /kg) from 1950 until 1964.
In the early 1970s, the price rose rapidly due to increasing demand
for bismuth as a metallurgical additive to aluminium, iron and steel.
This was followed by a decline owing to increased world production,
stabilized consumption, and the recessions of 1980 and 1981-1982. In
1984, the price began to climb as consumption increased worldwide,
especially in the United States and Japan. In the early 1990s,
research began on the evaluation of bismuth as a nontoxic replacement
for lead in ceramic glazes, fishing sinkers, food-processing
equipment, free-machining brasses for plumbing applications,
lubricating greases, and shot for waterfowl hunting. Growth in these
areas remained slow during the middle 1990s, in spite of the backing
of lead replacement by the United States federal government, but
intensified around 2005. This resulted in a rapid and continuing
increase in price.
Recycling
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Most bismuth is produced as a byproduct of other metal-extraction
processes including the smelting of lead, and also of tungsten and
copper. Its sustainability is dependent on increased recycling, which
is problematic.
It was once believed that bismuth could be practically recycled from
the soldered joints in electronic equipment. Recent efficiencies in
solder application in electronics mean there is substantially less
solder deposited, and thus less to recycle. While recovering the
silver from silver-bearing solder may remain economic, recovering
bismuth is substantially less so.
Dispersed bismuth is used in certain stomach medicines (bismuth
subsalicylate), paints (bismuth vanadate), pearlescent cosmetics
(bismuth oxychloride), and bismuth-containing bullets. Recycling
bismuth from these uses is impractical.
Applications
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Bismuth has few commercial applications, and those applications that
use it generally require small quantities relative to other raw
materials. In the United States, for example, 733 tonnes of bismuth
were consumed in 2016, of which 70% went into chemicals (including
pharmaceuticals, pigments, and cosmetics) and 11% into bismuth alloys.
In the early 1990s, researchers began to evaluate bismuth as a
nontoxic replacement for lead in various applications.
Medicines
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Bismuth is an ingredient in some pharmaceuticals, although the use of
some of these substances is declining.
* Bismuth subsalicylate is used to treat diarrhea; it is the active
ingredient in such "pink bismuth" preparations as Pepto-Bismol, as
well as the 2004 reformulation of Kaopectate. It is also used to treat
some other gastro-intestinal diseases like shigellosis and cadmium
poisoning. The mechanism of action of this substance is still not well
documented, although an oligodynamic effect (toxic effect of small
doses of heavy metal ions on microbes) may be involved in at least
some cases. Salicylic acid from hydrolysis of the compound is
antimicrobial for toxogenic 'E. coli,' an important pathogen in
traveler's diarrhea.
* A combination of bismuth subsalicylate and bismuth subcitrate is
used to treat the bacteria causing peptic ulcers.
* Bibrocathol is an organic bismuth-containing compound used to treat
eye infections.
* Bismuth subgallate, the active ingredient in Devrom, is used as an
internal deodorant to treat malodor from flatulence and feces.
* Bismuth compounds (including sodium bismuth tartrate) were formerly
used to treat syphilis. Arsenic combined with either bismuth or
mercury was a mainstay of syphilis treatment from the 1920s until the
advent of penicillin in 1943.
* "Milk of bismuth" (an aqueous suspension of bismuth hydroxide and
bismuth subcarbonate) was marketed as an alimentary cure-all in the
early 20th century, and has been used to treat gastrointestinal
disorders.
* Bismuth subnitrate (Bi5O(OH)9(NO3)4) and bismuth subcarbonate
(Bi2O2(CO3)) are also used in medicine.
Cosmetics and pigments
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Bismuth oxychloride (BiOCl) is sometimes used in cosmetics, as a
pigment in paint for eye shadows, hair sprays and nail polishes. This
compound is found as the mineral bismoclite and in crystal form
contains layers of atoms (see figure above) that refract light
chromatically, resulting in an iridescent appearance similar to nacre
of pearl. It was used as a cosmetic in ancient Egypt and in many
places since. 'Bismuth white' (also "Spanish white") can refer to
either bismuth oxychloride or bismuth oxynitrate (BiONO3), when used
as a white pigment. Bismuth vanadate is used as a light-stable
non-reactive paint pigment (particularly for artists' paints), often
as a replacement for the more toxic cadmium sulfide yellow and
orange-yellow pigments. The most common variety in artists' paints is
a lemon yellow, visually indistinguishable from its cadmium-containing
alternative.
Transistors
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Bismuth-based transistors has been claimed to enable smaller, faster,
and more energy-efficient transistors than traditional silicon.
Bismuth offers a small bandgap and high electron mobility. It has
topological insulator states, conducting along its surface/edges while
still insulating internally. It can produce two-dimensional(2D)
semiconductor materials, enabling thinner and higher-performance
devices. Such 2D bismuth materials support sub-nanometer channel
lengths, surpassing silicon's practical limits. However, bismuth's
anisotropic heat transport can complicate chip design.
Bismuth telluride () has been investigated for use in thermoelectric
transistors that use temperature gradients (e.g., via laser
illumination) to generate electricity, yielding 0.7093 μW in
experimental setups. They operate by leveraging the Seebeck effect,
using a temperature difference to drive charge carrier movement.
Bismuth oxyselenide ( and ) have been investigated for use in
field-effect transistors (FETs). These 2D materials exhibit high
electron mobility (e.g., 10-15 cm2 V⁻¹ s⁻¹) and stability in air. One
study reported that these materials enabled transistors that were 40%
faster and 10% more efficient than Intel’s 3 nm chips.
Bismuth can reduce contact resistance when paired with 2D
semiconductors such as . This eliminates the Schottky barrier--a
common efficiency issue in metal-semiconductor interfaces.
Metal and alloys
==================
Bismuth is used in alloys with other metals such as tin and lead.
Wood's metal, an alloy of bismuth, lead, tin, and cadmium, is used in
automatic sprinkler systems for fires. It forms the largest part (50%)
of Rose's metal, a fusible alloy, which also contains 25-28% lead and
22-25% tin. It was also used to make bismuth bronze, which was used
during the Bronze Age, having been found in Inca knives at Machu
Picchu.
Lead replacement
==================
The density difference between lead (11.32 g/cm3) and bismuth (9.78
g/cm3) is small enough that for many ballistics and weighting
applications, bismuth can substitute for lead. For example, it can
replace lead as a dense material in fishing sinkers. It has been used
as a replacement for lead in shot, bullets and less-lethal riot gun
ammunition. The Netherlands, Denmark, England, Wales, the United
States, and many other countries now prohibit the use of lead shot for
the hunting of wetland birds, as many birds are prone to lead
poisoning owing to mistaken ingestion of lead (instead of small stones
and grit) to aid digestion, or even prohibit the use of lead for all
hunting, such as in the Netherlands. Bismuth-tin alloy shot is one
alternative that provides similar ballistic performance to lead.
Bismuth, as a dense element of high atomic weight, is used in
bismuth-impregnated latex shields to shield from X-ray in medical
examinations, such as CTs, mostly as it is considered non-toxic.
The European Union's Restriction of Hazardous Substances Directive
(RoHS) for reduction of lead has broadened bismuth's use in
electronics as a component of low-melting point solders, as a
replacement for traditional tin-lead solders. Its low toxicity will be
especially important for solders to be used in food processing
equipment and copper water pipes, although it can also be used in
other applications including those in the automobile industry, in the
European Union, for example.
Bismuth has been evaluated as a replacement for lead in free-machining
brasses for plumbing applications, although it does not equal the
performance of leaded steels.
Other metal uses and specialty alloys
=======================================
Many bismuth alloys have low melting points and are found in specialty
applications such as solders. Many automatic sprinklers, electric
fuses, and safety devices in fire detection and suppression systems
contain the eutectic In19.1-Cd5.3-Pb22.6-Sn8.3-Bi44.7 alloy that melts
at 47 C This is a convenient temperature since it is unlikely to be
exceeded in normal living conditions. Low-melting alloys, such as
Bi-Cd-Pb-Sn alloy which melts at 70 C, are also used in automotive and
aviation industries. Before deforming a thin-walled metal part, it is
filled with a melt or covered with a thin layer of the alloy to reduce
the chance of breaking. Then the alloy is removed by submerging the
part in boiling water.
Bismuth is used to make free-machining steels and free-machining
aluminium alloys for precision machining properties. It has similar
effect to lead and improves the chip breaking during machining. The
shrinking on solidification in lead and the expansion of bismuth
compensate each other and therefore lead and bismuth are often used in
similar quantities. Similarly, alloys containing comparable parts of
bismuth and lead exhibit a very small change (on the order 0.01%) upon
melting, solidification or aging. Such alloys are used in
high-precision casting, e.g. in dentistry, to create models and molds.
Bismuth is also used as an alloying agent in production of malleable
irons and as a thermocouple material.
Bismuth is also used in aluminium-silicon cast alloys to refine
silicon morphology. However, it indicated a poisoning effect on
modification of strontium. Some bismuth alloys, such as
Bi35-Pb37-Sn25, are combined with non-sticking materials such as mica,
glass and enamels because they easily wet them allowing to make joints
to other parts. Addition of bismuth to caesium enhances the quantum
yield of caesium cathodes. Sintering of bismuth and manganese powders
at 300 C produces a permanent magnet and magnetostrictive material,
which is used in ultrasonic generators and receivers working in the
10-100 kHz range and in magnetic and holographic memory devices.
Other uses as compounds
=========================
* Bismuth is included in BSCCO (bismuth strontium calcium copper
oxide), which is a group of similar superconducting compounds
discovered in 1988 that exhibit the highest superconducting transition
temperatures.
* Bismuth telluride is a semiconductor and an excellent thermoelectric
material. Bi2Te3 diodes are used in mobile refrigerators, CPU coolers,
and as detectors in infrared spectrophotometers.
* Bismuth oxide, in its delta form, is a solid electrolyte for oxygen.
This form normally breaks down below a high-temperature threshold, but
can be electrodeposited well below this temperature in a highly
alkaline solution.
* Bismuth germanate is a scintillator, widely used in X-ray and gamma
ray detectors.
* Bismuth vanadate is an opaque yellow pigment used by some artists'
oil, acrylic, and watercolor paint companies, primarily as a
replacement for the more toxic cadmium sulfide yellows in the
greenish-yellow (lemon) to orange-toned yellow range. It performs
practically identically to the cadmium pigments, such as in terms of
resistance to degradation from UV exposure, opacity, tinting strength,
and lack of reactivity when mixed with other pigments. The most
commonly-used variety by artists' paint makers is lemon in color. In
addition to being a replacement for several cadmium yellows, it also
serves as a non-toxic visual replacement for the older chromate
pigments made with zinc, lead, and strontium. If a green pigment and
barium sulfate (for increased transparency) are added it can also
serve as a replacement for barium chromate, which possesses a more
greenish cast than the others. In comparison with lead chromate, it
does not blacken due to hydrogen sulfide in the air (a process
accelerated by UV exposure) and possesses a particularly brighter
color than them, especially the lemon, which is the most translucent,
dull, and fastest to blacken due to the higher percentage of lead
sulfate required to produce that shade. It is also used, on a limited
basis due to its cost, as a vehicle paint pigment. Bismuth vanadate
can also be used as electrocatalyst for hydrogen peroxide synthesis.
* Bismuth tungstate can be used as photocatalyst for removal of
phenolic compounds as well as for hydrogen generation.
* Bismuth molybdate is a catalyst for propylene oxidation as well as
photocatalyst.
* A catalyst for making acrylic fibers.
* As an electrocatalyst in the conversion of CO2 to CO.
* Ingredient in lubricating greases.
* In crackling microstars (dragon's eggs) in pyrotechnics, as the
oxide, subcarbonate or subnitrate.
*As catalyst for the fluorination of arylboronic pinacol esters
through a Bi(III)/Bi(V) catalytic cycle, mimicking transition metals
in electrophilic fluorination.
Toxicology and ecotoxicology
======================================================================
:'See also bismuthia, a rare dermatological condition that results
from the prolonged use of bismuth.'
Scientific literature indicates that some of the compounds of bismuth
are less toxic to humans via ingestion than other heavy metals (lead,
arsenic, antimony, etc.) presumably due to the comparatively low
solubility of bismuth salts. Its biological half-life for whole-body
retention is reported to be 5 days but it can remain in the kidney for
years in people treated with bismuth compounds.
Bismuth poisoning can occur and has according to some reports been
common in relatively recent times. As with lead, bismuth poisoning can
result in the formation of a black deposit on the gingiva, known as a
bismuth line. Poisoning may be treated with dimercaprol; however,
evidence for benefit is unclear.
Bismuth's environmental impacts are not well known; it may be less
likely to bioaccumulate than some other heavy metals, and this is an
area of active research.
See also
======================================================================
* Bismuth minerals
* Arsenic-bismuth
Cited sources
======================================================================
.
*
*
*
*
External links
======================================================================
* [
http://www.periodicvideos.com/videos/083.htm Bismuth] at 'The
Periodic Table of Videos' (University of Nottingham)
* [
http://www.amazingrust.com/Experiments/how_to/Bismuth_Crystals.html
Bismuth Crystals - Instructions & Pictures]
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=========
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Original Article:
http://en.wikipedia.org/wiki/Bismuth
