Agnes Pockels

German chemist (1862–1935)

Agnes Luise Wilhelmine Pockels (14 February 1862 – 21 November 1935) was a German chemist whose research was fundamental in establishing the modern discipline known as surface science, which describes the properties of liquid and solid surfaces and interfaces. Pockels became interested in fundamental research in surface science through observations of soaps and soapy water in her own home while washing dishes. She devised a surface film balance technique to study the behavior of molecules such as soaps and surfactants at air liquid interfaces. From these studies, Pockels defined the "Pockels Point" which is the minimum area that a single molecule can occupy in monomolecular films. Pockels was an autodidact. She was not a paid, professional scientist and had no institutional affiliation and so is an example of a citizen scientist. By contrast, her brother Friedrich Carl Alwin Pockels, for whom the Pockels effect was named, was a professor of theoretical physics at the University of Heidelberg.

Pockels was born in Venice, Austrian Empire, in 1862. At the time, Venice was under Austrian rule, and Pockels' father served in the Austrian Army. When he fell sick, the family moved in 1871 to Brunswick, which was part of the nascent German Empire. Agnes was interested in chemistry as a child. However, women were not allowed to enter universities to study. Pockels stated that "I had a passionate interest in natural science, especially physics, and would have liked to study.“ (Agnes Pockels, as translated by Giles from Autobiographical Notes in W. Ostwald, 1932. Pockels further developed her apparatus by placing a small disk (typically 6 millimeters in diameter), such as a button, on the surface of the water in the trough. She then used a weighing scale (typically an apothecary's balance) to determine the force (weight) necessary to lift the disk from the water. By comparing the forces required to lift the disk from pure water to water containing impurities, she devised a direct measure of surface tension. This apparatus enabled her to investigate the surface forces of mono molecular films, the surface tension of emulsions and solutions, the effect of impurities on the physical properties of water, and providing an understanding of surfactancy. Pockels' design influenced later investigators who improved on the method, leading to the modern Langmuir Blodgett trough which is in extensive use in colloid and surface science in contemporary times. Her first paper was "Surface Tension," describing her measurements and findings with her sliding trough. The letter to Lord Rayleigh was described in a 1971 journal article on the origin of the surface film balance as being "a landmark in the history of surface chemistry. Pockels described the calming effect that oils can have on bodies of water, Her research extended to investigations of other surface phenomena including capillarity and contact angles. She was eventually recognized as a pioneer in the emerging field of surface science. Following the death of her brother, Friedrich Carl Alwin Pockels in 1913 and her own ill health, Agnes Pockels lost contact with many professional scientists and ceased original research.

Pockels spent much of her life caring for her sick parents, which she noted to be "very challenging". Her father died in 1906 and her mother died in 1914. By that time, Pockels was herself in ill health, necessitating a stay for a time in a sanatorium. She traveled in Europe for enjoyment. Using an improved version of this slide trough, American chemist Irving Langmuir made additional discoveries on the properties of surface molecules, which earned him a Nobel Prize in chemistry in 1932. Pockels' device is a direct antecedent of the Langmuir–Blodgett trough, developed later by Langmuir and physicist Katharine Blodgett. Since 1993, the Technical University Braunschweig has awarded the Agnes Pockels Medal to people who have advanced the Technical University Braunschweig, emphasizing those who have promoted teaching and research especially women. The Agnes Pockels Laboratory was established at the Technical University Braunschweig in 2002. Its purpose is to foster chemical education, aid chemistry teachers, and encourage young children in the pursuit of the natural sciences. It emphasizes children under the age of 10, especially girls. In this laboratory, children experience learning by doing, much like a craft, without theoretical knowledge or advanced instrumentation. The Ostwald article includes a list of her publication and a summary of several of them. It also includes autobiographical passages from Pockels.

C. H. Giles and S. D. Forrester, "The origins of the surface film balance: Studies in the early history of surface chemistry, part 3", Chemistry and Industry, pp. 43–53 (9 January 1971). (Note: This article contains one of the most detailed stories on Agnes Pockels, including photos of her and her family.) Charles Tanford, Ben Franklin stilled the waves: An informal history of pouring oil on water with reflections on the ups and downs of scientific life in general, Oxford University Press, 2004. M. Elizabeth Derrick, "Agnes Pockels, 1862 1935", Journal of Chemical Education, vol. 59, no. 12, pp. 1030–1031 (Dec. 1982). Andrea Kruse and Sonja M. Schwarzl. "Zum Beispiel Agnes Pockels." In: Nachrichten aus der Chemie, 06, 2002.