21 February 2015

Ultramicroscope




The invention: 

A microscope characterized by high-intensity illumination
for the study of exceptionally small objects, such as colloidal
substances.


The people behind the invention:

Richard Zsigmondy (1865-1929), an Austrian-born German
organic chemist who won the 1925 Nobel Prize in Chemistry
H. F. W. Siedentopf (1872-1940), a German physicist-optician
Max von Smouluchowski (1879-1961), a German organic
chemist.





Accidents of Alchemy

Richard Zsigmondy’s invention of the ultramicroscope grew out
of his interest in colloidal substances. Colloids consist of tiny particles
of a substance that are dispersed throughout a solution of another
material or substance (for example, salt in water). Zsigmondy
first became interested in colloids while working as an assistant to
the physicist Adolf Kundt at the University of Berlin in 1892. Although
originally trained as an organic chemist, in which discipline
he took his Ph.D. at the University of Munich in 1890, Zsigmondy
became particularly interested in colloidal substances containing
fine particles of gold that produce lustrous colors when painted on
porcelain. For this reason, he abandoned organic chemistry and devoted
his career to the study of colloids.
Zsigmondy began intensive research into his new field of interest
in 1893, when he returned to Austria to accept a post as lecturer at a
technical school at Graz. Zsigmondy became especially interested
in gold-ruby glass, the accidental invention of the seventeenth century
alchemist Johann Kunckle. Kunckle, while pursuing the alchemist’s
pipe dream of transmuting base substances (such as lead)
into gold, discovered instead a method of producing glass with a
beautiful, deep red luster by suspending very fine particles of gold
throughout the liquid glass before it was cooled. Zsigmondy also
began studying a colloidal pigment called “purple of Cassius,” the
discovery of another seventeenth century alchemist, Andreas Cassius.
Zsigmondy soon discovered that purple of Cassius was a colloidal
solution and not, as most chemists believed at the time, a chemical
compound. This fact allowed him to develop techniques for
glass and porcelain coloring with great commercial value, which led
directly to his 1897 appointment to a research post with the Schott
Glass Manufacturing Company in Jena, Germany. With the Schott
Company, Zsigmondy concentrated on the commercial production
of colored glass objects. His most notable achievement during this
period was the invention of Jena milk glass, which is still prized by
collectors throughout the world.


Brilliant Proof


While studying colloids, Zsigmondy devised experiments that
proved that purple of Cassius was colloidal. When he published the
results of his research in professional journals, however, they were
not widely accepted by the scientific community. Other scientists
were not able to replicate Zsigmondy’s experiments and consequently
denounced them as flawed. The criticism of his work in
technical literature stimulated Zsigmondy to make his greatest discovery,
the ultramicroscope, which he developed to prove his theories
regarding purple of Cassius.
The problem with proving the exact nature of purple of Cassius
was that the scientific instruments available at the time were not
sensitive enough for direct observation of the particles suspended
in a colloidal substance. Using the facilities and assisted by the staff
(especially H. F.W. Siedentopf, an expert in optical lens grinding) of
the Zeiss Glass Manufacturing Company of Jena, Zsigmondy developed
an ingenious device that permitted direct observation of individual
colloidal particles.
This device, which its developers named the “ultramicroscope,”
made use of a principle that already existed. Sometimes called “darkfield
illumination,” this method consisted of shining a light (usually
sunlight focused by mirrors) through the solution under the microscope
at right angles to the observer, rather than shining the light directly
from the observer into the solution. The resulting effect is similar
to that obtained when a beam of sunlight is admitted to a closed
room through a small window. If an observer stands back fromand at
right angles to such a beam, many dust particles suspended in the air
will be observed that otherwise would not be visible.
Zsigmondy’s device shines a very bright light through the substance
or solution being studied. From the side, the microscope then
focuses on the light shaft. This process enables the observer using
the ultramicroscope to view colloidal particles that are ordinarily
invisible even to the strongest conventional microscope. To a scientist
viewing purple of Cassius, for example, colloidal gold particles
as small as one ten-millionth of a millimeter in size become visible.

Impact

After Zsigmondy’s invention of the ultramicroscope in 1902,
the University of Göttingen appointed him professor of inorganic
chemistry and director of its Institute for Inorganic Chemistry.
Using the ultramicroscope, Zsigmondy and his associates quickly
proved that purple of Cassius is indeed a colloidal substance.
That finding, however, was the least of the spectacular discoveries
that resulted from Zsigmondy’s invention. In the next decade,
Zsigmondy and his associates found that color changes in colloidal
gold solutions result from coagulation—that is, from changes in the
size and number of gold particles in the solution caused by particles
bonding together. Zsigmondy found that coagulation occurs when
the negative electrical charge of the individual particles is removed
by the addition of salts. Coagulation can be prevented or slowed by
the addition of protective colloids.
These observations also made possible the determination of the
speed at which coagulation takes place, as well as the number of particles
in the colloidal substance being studied.With the assistance of
the organic chemist Max von Smouluchowski, Zsigmondy worked
out a complete mathematical formula of colloidal coagulation that is
valid not only for gold colloidal solutions but also for all other
colloids. Colloidal substances include blood and milk, which both coagulate,
thus giving Zsigmondy’s work relevance to the fields of
medicine and agriculture. These observations and discoveries concerning
colloids—in addition to the invention of the ultramicroscope—
earned for Zsigmondy the 1925 Nobel Prize in Chemistry.




Richard Zsigmondy

Born in Vienna, Austria, in 1865, Richard Adolf Zsigmondy
came from a talented, energetic family. His father, a celebrated
dentist and inventor of medical equipment, inspired his children
to study the sciences, while his mother urged them to
spend time outdoors in strenuous exercise. Although his father
died when Zsigmondy was fifteen, the teenager’s interest in
chemistry was already firmly established. He read advanced
chemistry textbooks and worked on experiments in his own
home laboratory.
After taking his doctorate at the University of Munich and
teaching in Berlin and Graz, Austria, he became an industrial
chemist at the glassworks in Jena, Germany. However, pure research
was his love, and he returned to it, working entirely on
his own after 1900. In 1907 he received an appointment as professor
and director of the Institute of Inorganic Chemistry at the
University of Göttingen, one of the scientific centers of the
world. There he accomplished much of his ground-breaking
work on colloids and Brownian motion, despite the severe
shortages that hampered him during the economic depression
in Germany following World War I. His 1925 Nobel Prize in
Chemistry, especially the substantial money award, helped him
overcome his supply problems. He retired in early 1929 and
died seven months later.

See also:  Scanning tunneling microscope; Ultracentrifuge;

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