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تاريخ التسجيل : 16/02/2011
 |  موضوع: Robert Bunsen  الخميس مارس 31, 2011 5:21 am | |
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Robert Wilhelm Bunsen (1811-1899)
Bunsen
was born on March 31, 1811 in Göttingen, Germany, the youngest of four
sons. As his father was a professor of modern languages at the
university, an academic environment would surround him from birth. After
schooling in the city of Holzminden, Bunsen studied chemistry at
Göttingen. Receiving his doctorate at age 19, Bunsen set off on
extensive travels, partially underwritten by the government, that took
him through Germany and Paris and eventually to Vienna from 1830 to
1833. During this time, Bunsen visited Henschel's machinery
manufacturing plant and saw the "new small steam engine." In Berlin, he
saw the mineralogical collections of Weiss and had contact with Runge,
the discoverer of aniline. Continuing on his journeys, Bunsen met with
Liebig in Giessen and with Mitscherlich in Bonn for a geological trip
through the Eifel mountains.<table style="border-collapse: collapse;" id="AutoNumber1" border="0" cellpadding="0" cellspacing="0" width="100%"><tr><td width="26%"> </td><td width="74%">The
essential piece of laboratory equipment that has immortalized the name
of Robert Wilhelm Bunsen was not invented by him. Bunsen improved the
burner's to aid his endeavors in spectroscopy. Ironically, Bunsen will
be remembered by generations of chemistry students for a mere
improvement in a burner , when his other contributions to the field of
chemistry are vastly more significant and diverse, covering such areas
as organic chemistry, arsenic compounds, gas measurements and analysis,
the galvanic battery, elemental spectroscopy and geology.In Paris and
Vienna, Bunsen visited the Sevres porcelain works and met with the
outstanding chemists of the times. These travels allowed Bunsen the
opportunity to establish a network of contacts that would stay with him
throughout his illustrious career. </td></tr></table>Upon
his return to Germany, Bunsen became a lecturer at Göttingen and began
his experimental studies of the insolubility of metal salts of arsenious
acid. His discovery of the use of iron oxide hydrate as a precipitating
agent is still the best known antidote against arsenic poisoning to
this day. This was his only venture in organic/physiological chemistry.
In 1836, Bunsen was nominated to succeed Wöhler at Kassel. He taught
there for two years before accepting a position at the University of
Marsburg which was the site of his important and dangerous studies of
cacodyl derivatives. This research was his only work in pure organic
chemistry and made him immediately famous within the scientific
community. Cacodyl (from the Greek kakodhs - "stinking") was also known
as alkarsine or "Cadet's liquid," a product made from arsenic distilled
with potassium acetate. The chemical composition of this liquid was
unknown, but it and its compounds were known to be poisonous, highly
flammable and had an extremely nauseating odor even in minute
quantities. Bunsen himself described one of these compounds: "the smell
of this body produces instantaneous tingling of the hands and feet, and
even giddiness and insensibility...It is remarkable that when one is
exposed to the smell of these compounds the tongue becomes covered with a
black coating, even when no further evil effects are noticeable."Bunsen's
daring experiments showed that cacodyl was an oxide of arsenic that
contained a methyl radical (a group of atoms acting as one species).
These results significantly furthered the earlier work by Gay-Lussac,
who had isolated the radical cyan in 1815, and that of Liebig and Wöhler
who published "One the radical of benzoic acid" in 1832. Typical of his
research life, however, Bunsen seemed content to explore subjects of
interest in his lab, but remained outside the fray that surrounded the
often "violent" discussions of theoretical subjects. Although Bunsen's
work brought him quick and wide acclaim, he nearly killed himself from
arsenic poisoning and it also cost him the sight of one eye - an
explosion of the compound sent a sliver of glass into his eye.While
at Marsburg, Bunsen studied blast furnaces and demonstrated that over
half the heat was lost in the charcoal-burning German furnaces. In
British furnaces, over 80% was lost. Bunsen and a collaborator, Lyon
Playfair, suggested techniques that could recycle gases through the
furnace and retrieve valuable escaping by-products such as ammonia.
Other work during this period concentrated on technological experiments
such as the generation of galvanic currents in batteries. In 1841,
instead of the expensive platinum electrode used in Grove's battery,
Bunsen made a carbon electrode. This led to large scale use of the "Bunsen battery" in the production of arc-light and in electroplating.One
of the more memorable episodes during Bunsen's tenure at Marsburg was a
geological trip to Iceland sponsored by the Danish government following
the eruption of Mount Hekla in 1845. Indulging his lifelong interest in
geology, Bunsen collected gases emitted from volcanic vents and
performed extensive chemical analyses of volcanic rock. In addition to
sampling lava gases, Bunsen investigated the theory of geyser action.
The popular belief of his time was that the water
from geysers was volcanic in origin. Bunsen took rocks from the area
and boiled them in rain water. He found that the resulting solution was
quite similar to geyser water. He conducted temperature studies on the
water in the geyser tube at different depths and discovered that the
water was indeed hot enough to boil. Due to pressure differentials
caused by the moving column of water, boiling occurs in the middle of
the tube and throws the mass of water above it into the sky above. In true investigative spirit Bunsen experimented with an artificial geyser in the lab:"To
confirm his theory, Bunsen made an artificial geyser, consisting of a
basin of water having a long tube extending below it. He heated the tube
at the bottom andat about the middlepoint. As the water at the middle
reached its boiling point, all of the phenomena of geyser action were
beautifully shown, including the preliminary thundering. That was in
1846. From that day to this Bunsen's theory of geyser action has been
generally accepted by geologists."In 1852 Bunsen succeeded
Leopold Gmelin at Heidelberg. His stature was such that he attracted
students and chemists from all over the world to study in his
laboratory. Again, Bunsen ignored the current trend in organic chemistry
which was fast overtaking the experimental world. Instead, Bunsen
improved his earlier work on batteries: using chromic acid instead of
nitric acid, he was able to produce pure metals such as chromium,
magnesium, aluminum, manganese, sodium, aluminum, barium, calcium and
lithium by electrolysis. Bunsen devised a sensitive ice calorimeter that
measured the volume rather than the mass of the ice melted. This
allowed him to measure the metals' specific heat to find their true
atomic weights. During this period, he also pressed magnesium into wire.
The element came into general use as an outstanding illuminating agent.A
former student of Bunsen's believes that it was this "splendid light"
from the combustion of magnesium that led Bunsen to devote considerable
attention to photochemical studies. A ten year collaboration with Sir
Henry Roscoe began in 1852. They took equal volumes of gaseous hydrogen
and chlorine and studied the formation of HCl, which occurs in specific
relationship to the amount of light received. Their results showed that
the light radiated from the sun per minute was equivalent to the
chemical energy of 25 x 1012 mi3 of a hydrogen-chlorine mixture forming
HCl. In 1859, Bunsen suddenly discontinued his work with Roscoe, telling
him:At present Kirchhoff and I are engaged in a common work
which doesn't let us sleep...Kirchhoff has made a wonderful, entirely
unexpected discovery in finding the cause of the dark lines in the solar
spectrum....thus a means has been found to determine the composition of
the sun and fixed stars with the same accuracy as we determine sulfuric
acid, chlorine, etc., with our chemical reagents. Substances on the
earth can be determined by this method just as easily as on the sun, so
that, for example, I have been able to detect lithium in twenty grams of
sea water."Gustav
Kirchhoff, a young Prussian physicist, had the brilliant insight to use
a prism to separate the light into its constituent rays, instead of
looking through colored glass to distinguish between similarly colored
flames. Thus the fledgling science of spectroscopy, which would develop
into a vital tool for chemical analysis, was born. In order to study the
resultant spectra, however, a high temperature, nonluminous flame was
necessary. An article published by Bunsen and Kirchhoff in 1860 states:"The
lines show up the more distinctly the higher the temperature and the
lower the luminescence of the flame itself. The gas burner described by
one of us has a flame of very high temperature and little luminescence
and is, therefore, particularly suitable for experiments on the bright
lines that are characteristic for these substances."The
burner described was quickly dubbed the "Bunsen burner," although the
apparatus is not of his design. The concept to premix the gas and air
prior to combustion in order to yield the necessary high temperature,
nonluminous flame belongs to Bunsen. Credit for the actual design and
manufacture of the burner goes to Peter Desaga, a technician at the
University of Heidelburg. Within five years of the development of the
burner, Bunsen and Kirchhoff were deeply involved with spectroscopy,
inventing yet another instrument: the Bunsen-Kirchhoff spectroscope.
This vital instrument of chemical analysis can trace its ancestry to
such simple components as a "prism, a cigar box, and two ends of
otherwise unusable old telescopes." From such humble beginnings came the
instrument which proved to be of tremendous importance in chemical
analysis and the discovery of new elements.In addition to
yielding a unique spectrum for each element, the spectroscope had the
advantage of definite identification while only using a minimal amount
of sample, on the range of nanograms to micrograms for elements like
sodium and barium respectively. Using the techniques they devised,
Bunsen and Kirchhoff announced the discovery of cesium (Latin caesium,
"sky blue") in the following passage:"Supported by unambiguous
results of the spectral-analytical method, we believe we can state
right now that there is a fourth metal in the alkali group besides
potassium, sodium, and lithium, and it has a simple characteristic
spectrum like lithium; a metal that shows only two lines in our
apparatus: a faint blue one, almost coinciding with Srd, and another
blue one a little further to the violet end of the spectrum and as
strong and as clearly defined as the lithium line."In 1861,
only a few months following their cesium discovery, Bunsen and Kirchhoff
announced the discovery of yet another new alkali metal. Two hitherto
undiscovered violet spectral lines in an alkali of the mineral
lepidolite were attributed to a new element, rubidium. Bunsen and
Kirchhoff's combined genius quickly paved the way for others to claim
elemental discoveries. The spectroscope served as a springboard by which
five new elements were discovered. These included thallium (Crookes,
1861), indium (Reich and Richter, 1863), gallium (Lecoq de Boisbaudran,
1875), scandium (Nilson, 1879) and germanium (Winkler, 1886). Fittingly,
Bunsen's original vision of analyzing the composition of the stars was
realized in 1868 when helium was discovered in the solar spectrum.Throughout
his professional life, Bunsen's personal life centered around his
laboratory and his students. Never marrying, Bunsen often took on the
introductory courses that were shunned by other colleagues. During the
one hundred hours of lectures presented each semester, Bunsen emphasized
experimentation and tabulated summaries and patiently introduced
students to the world of analytical chemistry. Bunsen's habit was to
assign a scientific task to his students and then to work with a student
only as long as required to reach some measure of independence. Many
principal players in the history of chemistry can trace their chemical
roots back to Bunsen's laboratory. Two of his more famous students were
Dmitri Mendeleev and Lothar Meyer. According to accounts, Bunsen was one
of the more modest of giants:"He never said: 'I have
discovered,' or 'I found'...He was characterized by extraordinary,
distinguished modesty. That does not mean that he was not conscious of
his own value. He knew how to use it at the right time and in the right
company; he even had a considerable degree of very sound egotism."The
scientific world held Bunsen in high esteem for much of his long
professional life. In 1842 he was elected to the Chemical Society of
London and the Academie des Sciences in 1853. He was named a foreign
fellow of the Royal Society of London in 1858, receiving its Copley
Medal in 1860. Bunsen and Kirchhoff were recipients of the first Davy
Medal in 1877. The Albert Medal was awarded in 1898 in recognition of
Bunsen's many scientific contributions to industry. Of these honors,
Bunsen once remarked,"Such things had value for me only because they
pleased my mother; she is now dead."Upon his retirement at the
age of 78, Bunsen left the chemical work behind, returned to his first
love of geology, keeping up with the latest developments in the field
and corresponding with his old friends such as Roscoe, Kirchhoff and
Helmholtz. Bunsen died August 16, 1899 after a peaceful three day sleep,
leaving behind a glowing legacy of discoveries and technological
advances that allowed the world of chemistry to burn brightly. (reference: http://step.sdsc.edu/projects95/chem.in.history/essays/bunsen.html) | </tr>
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