Ultramicroscope (Inventions)

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 “dark-field 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 from and at

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 text topics 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 Gottingen, 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.
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.


After Zsigmondy’s invention of the ultramicroscope in 1902, the University of Gottingen 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 ultramicro-scope—earned for Zsigmondy the 1925 Nobel Prize in Chemistry.
See also Scanning tunneling microscope; Ultracentrifuge; X-ray crystallography.

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