Agnes Luise Wilhelmine Pockels (14 February 1862 – 21 November 1935) was a
German
German(s) may refer to:
* Germany (of or related to)
** Germania (historical use)
* Germans, citizens of Germany, people of German ancestry, or native speakers of the German language
** For citizens of Germany, see also German nationality law
**Ge ...
chemist
A chemist (from Greek ''chēm(ía)'' alchemy; replacing ''chymist'' from Medieval Latin ''alchemist'') is a scientist trained in the study of chemistry. Chemists study the composition of matter and its properties. Chemists carefully describe t ...
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
soap
Soap is a salt of a fatty acid used in a variety of cleansing and lubricating products. In a domestic setting, soaps are surfactants usually used for washing, bathing, and other types of housekeeping. In industrial settings, soaps are use ...
s 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
Surfactants are chemical compounds that decrease the surface tension between two liquids, between a gas and a liquid, or interfacial tension between a liquid and a solid. Surfactants may act as detergents, wetting agents, emulsifiers, foaming ...
at air-liquid
interfaces. From these studies, Pockels defined the "Pockels Point" which is the minimum
area
Area is the quantity that expresses the extent of a region on the plane or on a curved surface. The area of a plane region or ''plane area'' refers to the area of a shape or planar lamina, while '' surface area'' refers to the area of an ope ...
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.
Early life and education
Pockels was born in
Venice
Venice ( ; it, Venezia ; vec, Venesia or ) is a city in northeastern Italy and the capital of the Veneto region. It is built on a group of 118 small islands that are separated by canals and linked by over 400 bridges. The isla ...
, Italy, in 1862. At the time, Venice was under Austrian rule, and Pockels' father served in the
Austrian Army
The Austrian Armed Forces (german: Bundesheer, lit=Federal Army) are the combined military forces of the Republic of Austria.
The military consists of 22,050 active-duty personnel and 125,600 reservists. The military budget is 0.74% of nati ...
. When he fell sick, the family moved in 1871 to
Brunswick, which was part of the nascent
German Empire.
There, Pockels attended the Municipal High School for Girls.
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.
)
As a child, Pockels was interested in science, especially physics. In those days, women in Germany had no access to universities.
Pockels studied science at home while caring for her parents. Pockels' younger brother
Friedrich Carl Alwin Pockels
Friedrich Carl Alwin Pockels (18 June 1865 – 29 August 1913) was a German physicist. He was born in Italy to Captain Theodore Pockels and Alwine Becker. He obtained a doctorate from the University of Göttingen in 1888, and from 1900 to 1913 h ...
studied physics at the University of Göttingen, completing his degree there. Friedrich shared textbooks from the university with Agnes Pockels in order to help her study from home. He later shared academic literature with Agnes Pockels to advance her studies.
Scientific investigations
Initial findings
![Ksv-nima-medium-lb01](https://upload.wikimedia.org/wikipedia/commons/b/b7/Ksv-nima-medium-lb01.jpg)
Through her experiences carrying out domestic chores, especially dishwashing, Pockels became interested in the effect of soaps on water and more generally on the effect of impurities on water and soapy water. By age 18, she began conducting experiments in her home to understand the physical properties of water and impurities, as an
amateur chemist.
As a result of her interests, by age 20, Pockels devised a slide trough for making quantitative measurements on the surface properties of soapy water and related substances. Specifically, this consisted of a trough, made of metal and rectangular in shape, roughly 70 centimeters (cm) long, 5 cm wide, and 2 cm deep. The trough was filled with water. A metal strip of about 1.5 cm width was laid on top of the water across the width of the trough so as to divide the surface of the water in two parts. There was a
ruler
A ruler, sometimes called a rule, line gauge, or scale, is a device used in geometry and technical drawing, as well as the engineering and construction industries, to measure distances or draw straight lines.
Variants
Rulers have long ...
along the length of the trough so that the position of the metal strip, and therefore the
surface area of each of the two parts of the trough, could be determined as the strip was moved along the length of the trough.
Pockels further developed her apparatus by placing a small disk (typically 6 millimeters in diameter), such as a
button
A button is a fastener that joins two pieces of fabric together by slipping through a loop or by sliding through a buttonhole.
In modern clothing and fashion design, buttons are commonly made of plastic but also may be made of metal, wood, o ...
, on the surface of the water in the trough. She then used a
weighing scale
A scale or balance is a device used to measure weight or mass. These are also known as mass scales, weight scales, mass balances, and weight balances.
The traditional scale consists of two plates or bowls suspended at equal distances from a ...
(typically an
apothecary's balance) to determine the force (
weight
In science and engineering, the weight of an object is the force acting on the object due to gravity.
Some standard textbooks define weight as a vector quantity, the gravitational force acting on the object. Others define weight as a scalar qua ...
) 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' sliding trough design built on the prior findings of
Ludwig Wilhelmy's plate method of measuring surface tension.
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.
Pockels' point determination
Pockels used her sliding trough to evaluate the effect of small amounts of impurities on water. These impurities were typically household substances such as oils and soaps. With her apparatus, she measured the surface tension as the amount of force required to remove the disk from the surface of the water. Pockels found that small amounts of impurities could have a large effect on the surface tension of water, compared to pure water.
![Surfactant](https://upload.wikimedia.org/wikipedia/commons/0/03/Surfactant.jpg)
In particular, Pockels studied soapy water. Soaps are examples of
surfactants
Surfactants are chemical compounds that decrease the surface tension between two liquids, between a gas and a liquid, or interfacial tension between a liquid and a solid. Surfactants may act as detergents, wetting agents, emulsifiers, foaming ...
, which are molecules which have a
hydrophilic
A hydrophile is a molecule or other molecular entity that is attracted to water molecules and tends to be dissolved by water.Liddell, H.G. & Scott, R. (1940). ''A Greek-English Lexicon'' Oxford: Clarendon Press.
In contrast, hydrophobes are ...
portion of the molecule, while the remainder is
hydrophobic
In chemistry, hydrophobicity is the physical property of a molecule that is seemingly repelled from a mass of water (known as a hydrophobe). In contrast, hydrophiles are attracted to water.
Hydrophobic molecules tend to be nonpolar and, t ...
. These are
insoluble
In chemistry, solubility is the ability of a substance, the solute, to form a solution with another substance, the solvent. Insolubility is the opposite property, the inability of the solute to form such a solution.
The extent of the solubil ...
in the water and tend to reside on the surface of the water. When placing small amounts of the surfactants in her sliding trough, Pockels found that the effect on surface tension was small. However, once the slider on the surface of the trough passed a certain point, the effect on surface tension was large. When she plotted the surface tension on one axis of a graph compared to the position of the slider on her sliding trough, the graphical representation was a
compression isotherm.
Using her knowledge of chemistry, Pockels realized that the point of the compression isotherm at which the surface tension changes abruptly is the point at which a film of surfactant molecules that is continuous and one molecule thick is formed. This is a monolayer of the surfactant. Pockels further found that this threshold point is the same for a variety of surfactant soaps. Since she knew how much surfactant was in her sliding trough as well as the
area
Area is the quantity that expresses the extent of a region on the plane or on a curved surface. The area of a plane region or ''plane area'' refers to the area of a shape or planar lamina, while '' surface area'' refers to the area of an ope ...
covered by the monolayer film, she could calculate the area on the surface of the water occupied by single molecule. She calculated this area to be 20 square
angstroms
The angstromEntry "angstrom" in the Oxford online dictionary. Retrieved on 2019-03-02 from https://en.oxforddictionaries.com/definition/angstrom.Entry "angstrom" in the Merriam-Webster online dictionary. Retrieved on 2019-03-02 from https://www.m ...
(20 Å
2). Later, as her investigations became known in the scientific community, this area determined by the sliding trough became known as the Pockels Point.
First publication
In 1891, approximately ten years after Pockels' first surface tension measurements, through her brother Friedrich Pockels, she became aware that
John William Strutt, 3rd Baron Rayleigh
John William Strutt, 3rd Baron Rayleigh, (; 12 November 1842 – 30 June 1919) was an English mathematician and physicist who made extensive contributions to science. He spent all of his academic career at the University of Cambridge. Amo ...
ord Rayleighwas publishing studies of the effect of small amounts of oils on the surface of water. It was clear to her that Lord Rayleigh's research was closely related to her own. At the encouragement of her brother, Agnes Pockels wrote to Lord Rayleigh to describe her apparatus, her findings, and the fact that she was unable to publish her findings in the
scientific journals
In academic publishing, a scientific journal is a periodical publication intended to further the progress of science, usually by reporting new research.
Content
Articles in scientific journals are mostly written by active scientists such as s ...
of the time. Pockels' original correspondence with Rayleigh was in the German language and was translated for Rayleigh by his wife. In an act of generosity and unthreatened by correspondence from an unknown amateur, Rayleigh forwarded Pockels' findings to the journal ''
Nature
Nature, in the broadest sense, is the physical world or universe. "Nature" can refer to the phenomena of the physical world, and also to life in general. The study of nature is a large, if not the only, part of science. Although humans are ...
'' with a suitable cover letter to enable Pockels' findings to be published.
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.
" Lord Rayleigh retained his correspondence, and Pockels letter to him dated 10 January 1891 began:
"My Lord, – Will you kindly excuse my venturing to trouble you with a German letter on a scientific subject? Having heard of the fruitful researches carried on by you last year on the hitherto little understood properties of water surfaces, I thought it might interest you to know of my own observations on the subject. For various reasons I am not in a position to publish them in scientific periodicals, and I therefore adopt this means of communicating to you the most important of them."
The body of Pockels's letter to Rayleigh then described her sliding trough method, her initial findings, and her assessment of the limitations of her experimental methods.
The closing of her letter stated:
"I thought I ought not to withhold from you these facts which I have observed, although I am not a professional physicist; and again begging you to excuse my boldness, I remain, with sincere respect,
Yours faithfully,
(signed) Agnes Pockels"
Lord Rayleigh forwarded Pockels's correspondence to the editor of the journal ''Nature'', with a covering letter dated 2 March 1891. The editor at the time was
Sir Joseph Norman Lockyer who chose to publish the correspondence from Rayleigh and Pockels. The covering letter stated:
"I shall be obliged if you can find space for the accompanying translation of an interesting letter which I have received from a German lady, who with very homely appliances has arrived at valuable results respecting the behaviour of contaminated water surfaces. The earlier part of Miss Pockels' letter covers nearly the same ground as some of my own recent work, and in the main harmonises 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."
Ostwald's biography of Pockels reports that Pockels had initially approached physicists at the
University of Göttingen
The University of Göttingen, officially the Georg August University of Göttingen, (german: Georg-August-Universität Göttingen, known informally as Georgia Augusta) is a public research university in the city of Göttingen, Germany. Founded ...
about her findings and received no expression of interest.
Later career
![Agnes Pockels ca1892](https://upload.wikimedia.org/wikipedia/commons/9/97/Agnes_Pockels_ca1892.jpg)
Following the first publication, Pockels' studies of surface films accelerated. She continued to correspond with Lord Rayleigh. These communications emphasized her findings concerning the importance of purity and cleanliness of the equipment, including a recognition of difficulties in her own experimentation regarding previously unrecognized contamination.
Pockels pointed out that even
airborne dust can affect results with her experimental apparatus. She recognized that impurities can affect
reproducibility of experimental findings. Pockels developed a refined method of assessing monolayer films consisting of deposition of the compound on interest as a solution in benzene on the water surface in her sliding trough. Through this line of experimentation, she measured the thickness of certain monolayer films as being 13Å. With the aid of Lord Rayleigh, Pockels's second publication appeared in the journal ''Nature'' in 1892.
Pockels described the calming effect that oils can have on bodies of water,
an effect first investigated in the published literature by
Benjamin Franklin
Benjamin Franklin ( April 17, 1790) was an American polymath who was active as a writer, scientist, inventor, statesman, diplomat, printer, publisher, and political philosopher. Encyclopædia Britannica, Wood, 2021 Among the leading inte ...
.
Her research extended to investigations of other surface phenomena including
capillarity
Capillary action (sometimes called capillarity, capillary motion, capillary rise, capillary effect, or wicking) is the process of a liquid flowing in a narrow space without the assistance of, or even in opposition to, any external forces li ...
and
contact angle
The contact angle is the angle, conventionally measured through the liquid, where a liquid–vapor interface meets a solid surface. It quantifies the wettability of a solid surface by a liquid via the Young equation. A given system of solid, liq ...
s.
Pockels published 14 scientific papers, mostly in German journals, the last one being published in 1926.
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 never received a formal appointment for her scientific endeavors. Nevertheless, she published a number of
scholarly paper
Academic publishing is the subfield of publishing which distributes academic research and scholarship. Most academic work is published in academic journal articles, books or theses. The part of academic written output that is not formally pub ...
s and eventually received recognition as a pioneer in the new field of surface science. Commentators wrote: "When Langmuir received the Nobel Prize for Chemistry in 1932, for his work in investigating monolayers on solids and on liquids, part of his achievement was
..founded on original experiments first made with a button and a thin tray, by a young lady of 18 who had had no formal scientific training."
Personal life
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
A sanatorium (from Latin '' sānāre'' 'to heal, make healthy'), also sanitarium or sanitorium, are antiquated names for specialised hospitals, for the treatment of specific diseases, related ailments and convalescence. Sanatoriums are often ...
. She traveled in Europe for enjoyment.
During Pockels later years, she was known for her role as an aunt, "Auntie Agnes."
Pockels died in 1935 in
Brunswick,
Germany
Germany,, officially the Federal Republic of Germany, is a country in Central Europe. It is the second most populous country in Europe after Russia, and the most populous member state of the European Union. Germany is situated betwe ...
, in the town where she had lived for the duration of her career.
Awards and legacy
In 1931, together with
Henri Devaux
Henri Edgard Devaux (6 July 1862 – 14 March 1956) was a French botanist, biophysicist, and plant physiologist who worked on gas exchange and membranes. In his studies on thin films, he was one of the pioneers of surface chemistry and molecular ...
, Pockels received the Laura R. Leonard Prize from the . In the following year, the
Braunschweig University of Technology
Braunschweig () or Brunswick ( , from Low German ''Brunswiek'' , Braunschweig dialect: ''Bronswiek'') is a city in Lower Saxony, Germany, north of the Harz Mountains at the farthest navigable point of the river Oker, which connects it to the Nor ...
granted her an
honorary doctorate
An honorary degree is an academic degree for which a university (or other degree-awarding institution) has waived all of the usual requirements. It is also known by the Latin phrases ''honoris causa'' ("for the sake of the honour") or ''ad hon ...
, being the first woman to receive such an award.
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
A Langmuir–Blodgett trough (LB trough) is a laboratory apparatus that is used to compress monolayers of molecules on the surface of a given subphase (usually water) and measures surface phenomena due to this compression. It can also be used to ...
, 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
Learning by doing refers to a theory of education. This theory has been expounded by American philosopher John Dewey and Latinamerican pedagogue Paulo Freire. It's a hands-on approach to learning, meaning students must interact with their envir ...
, much like a craft, without theoretical knowledge or advanced instrumentation.
Lord Rayleigh kept the correspondence he received from Pockels and her brother Friedrich Pockels. Pockels maintained a diary. These documents and photographs of the Pockels family were retained in the library of the
Royal Society of Chemistry
The Royal Society of Chemistry (RSC) is a learned society (professional association) in the United Kingdom with the goal of "advancing the chemical sciences". It was formed in 1980 from the amalgamation of the Chemical Society, the Royal Instit ...
at
Burlington House.
On the occasion of Pockels' 70th birthday in 1932, German
colloid chemist Wolfgang Ostwald published a biography of Pockels.
The Ostwald article includes a list of her publication and a summary of several of them. It also includes
autobiographical passages from Pockels.
Her sister-in-law Elisabeth (the wife of Friedrich Pockels) also published a biography of Pockels, emphasizing her personal life.
Publications
* "Surface Tension", (1891) ''Nature'', 46, 437.
*
On the relative contamination of the water-surface by equal quantities of different substances, (1892) ''Nature'' 47, 418.
* "Relations between the surface tension and relative contamination of water surfaces", (1893) ''Nature'', 48, 152.
* "On the spreading of oil upon water", (1894) ''Nature'' 50, 223.
* "Beobachtungen über die Adhäsion verschiedener Flüssigkeiten an Glas", (Observations about the Adhesion of Different Liquids on Glass), (1898) ''Naturwissenschaftliche Rundschau'', 14, 190.
* "Randwinkel gesättigter Lösungen an Kristallen" (Contact Angles of Saturated Solutions on Crystals), (1899), ''Naturwissenschaftliche Rundschau'', 14, 383.
* "Untersuchungen von Grenzflächenspannungen mit der Cohäsionswaage", (Investigations of the Surface Tension with the Cohesion Balance), (1899) ''Annalen der Physik'', 67, 668.
* "Über das spontane Sinken der Oberflächenspannung von Wasser, wässerigen Lösungen und Emulsionen"', (On the Spontaneous Decrease of the Surface Tension of Water, Aqueous Solutions and Emulsions), (1902) ''Annalen der Physik'', 8, 854.
* "Über Randwinkel und Ausbreitung von Flüssigkeiten auf festen Körpern" (On Contact Angles and the Flow of Fluids on Solid Bodies), (1914) ''Physikalische Zeitschrift'', 15, 39.
* "Zur Frage der zeitlichen Veränderung der Oberflächenspannun"' (On the Changes of the Surface Tension with Time), (1916) ''Physikalische Zeitschrift'', 17, 141
* "Über die Ausbreitung reiner und gemischter Flüssigkeiten auf Wasser" (On the Spreading of Pure and Mixed Liquids on Water) (1916) ''Physikalische Zeitschrift'', 17, 142.
* "Die Anomalie der Wasseroberfläche" (The Anomalous State of the Water Surface) (1917) ''Die Naturwissenschaften'', 5, 137 u. 149.
* "Zur Frage der Ölflecke auf Seen" (On Oil Stains on Lakes) (1918) ''Die Naturwissenschaften'', 6, 118.
* "The measurement of surface tension with the balance" (1926) ''Science'' 64, 304.
See also
*
Timeline of women in science
This is a timeline of women in science, spanning from ancient history up to the 21st century. While the timeline primarily focuses on women involved with natural sciences such as astronomy, biology, chemistry and physics, it also includes women f ...
*
Langmuir-Blodgett trough
References
Additional resources
*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.
External links
in Contributions of 20th Century Women to Physics at UCLA
erman Erman Rašiti may refer to:
Given name
* Erman Bulucu (born 1989), Turkish footballer
* Erman Eltemur (born 1993), Turkish karateka
* Erman Güraçar (born 1974), Turkish footballer
* Erman Kılıç (born 1983), Turkish footballer
* Erman Kunter (b ...
* Th
Agnes Pockels Laboratoryat the Technical University of Braunschweig
*
{{DEFAULTSORT:Pockels, Agnes
1862 births
1935 deaths
19th-century German chemists
19th-century German physicists
19th-century German women scientists
20th-century German chemists
20th-century German physicists
20th-century German women scientists
Austro-Hungarian emigrants to Germany
German women chemists
German women physicists
Scientists from Braunschweig
People from the Duchy of Brunswick
Surface science