Agnes Pockels
1862-1953
1862
Agnes was born in Venice on 2/14/1862, at that time a part of the Austro-Hungarian Empire. Her father was stationed with the Royal Austrian Army. He retired and sometime between 1865-1871 the family moved to Brunswick Germany. Here Agnes attended the local girls school with a focus on religion and languages. She attended the Municipal High School for girls where she took a strong interest in natural science.
Universities were closed to women across Germany, but her brother Friedrich did not have those obstacles. He studied at the technical university Carolo-Wihelmina of Brunswick, the Albert Ludwigs university of Freiburg and at the Georg August university of Gottingen. He supplied Agnes wtih textbooks and notes from his studies allowing her to study the subjects on her own. Fredrich received his PhD in physics from Gottingen in 1888.
1878
As the sole caretaker of her ill parents, Agnes spent many hours observing the properties of water, oil, soap and other products of the kitchen. Little work had been published in that area. Agnes could discuss physics with her brother, but her primary focus was caregiver to their aging parents. While Friedrich examined the influence of electrostatic fields in the laboratory, Agnes observed changes in the surface chemistry of water in in the kitchen while washing dishes.
The interplay of oil and water have interested scientists for centuries. Benjamin Franklin's work on surface tension involved early experiments that observed the calming effect of oil on water, findings he communicated through letters to fellow scientists. But there was no experimental method to measure and test these observations.
With Fredrich’s help she brought her observations to the physicists in Germany, but she got no response.
1888
Agnes learned that Lord Rayleigh in England had published a few works relating to surface tension. She put all of her notes and observations into a long and detailed letter of her work. After reading the letter, Lord Rayleigh sent it, along with a note of recommendation, to the editors of Nature.
I shall be obliged if you can find space for the accompanying translation which I have received from a German lady, who with very homely appliances has arrived at valuable results respecting the behavior of contaminated water surfaces. The earlier part of Miss Pockels’ letter covers nearly the same ground as some of my won recent work, and in the main harmonizes with it. The later sections seem to me very suggestive, raising, if they do not fully answer, many important questions. I hope soon to find opportunity for repeating some of Miss Pockels’ experiments.
1893
Agnes continued to make observations and refine her techniques. She kept up correspondence with Lord Rayleigh over the years and published several more articles in Nature over the years. Eventually her work reached Germany and she was offered a position by Professor Voigt at the Physical Institute. For the next decade she continued her research on surface tension. After 1902, Agnes was forced to set her research aside to aid her parents. Just a few years later, in 1906 her father died, followed by her brother in WWI and just a year later her mother died in 1914.
1931
Agnes continued her work, and acknowledge for her work continued to grow. In 1931 she received the Laura Leonard Prize (along with H. Devaux) for her work on surface tension. She was awarded an honorary doctorate from the Carolina-Wihelmina University of Brunswick the following year. In honor of her 70th birthday her work was published by W. Ostwald in the journal Kolloid-Zeitschrift.
Agnes continued to write, publishing several more papers, the last in 1933.
Langmuir-Pockels Trough
The trough uses a long rectangular trough of tin, filled to the brim with water. The water is divided in two by a tin bridge which can move along the length of the trough. Prior to measurement, the bridge is swept across the water surface clearing it of impurities. Molecules can then be introduced, they disperse across the surface into a monolayer. The bridge is then moved back closing the exposed water, forcing the introduced molecules together until they interact with each other forming a single monolayer.
Surface tension is measured by lowering a small disc on the water surface, then observing how much lifting force is needed to break the disk away from the surface. Dividing that force, by the perimeter of the disk gives the value for surface tension.
Agnes found that surface tension was reduced when impurities were introduced. As the concentration of impurities increases as the bridge is reduced, surface tension is reduced further until the point that the density of impurities reaches a constant density, then the surface tension ceases to decrease. Once molecules can no longer be reduced, when they occupy a minimum area, this area on average is about two square angstroms.
By oscillating the surface at one end with a stick, she generated a wave that traveled down the trough. Agnes found that impurities would cause the wave to attenuate significantly faster. She found the surface could be visualized by sprinkling it with lycopodium.
In 1917 Irving Langmuir along with the help of Katharine Blodgett expanded on Pockels work, resulting in more detailed work on surface tension. The work led to a Nobel prize for Langmuir in 1932