Agnes Pockels - Making History at the Kitchen Sink

Prologue
Persons who lived in the past and contributed to the advancement of knowledge should be remembered by those of us who follow in time. Today, with the availability of the computer and the possibility of reaching many countries almost instantaneously, it is a much easier task to convey words of praise than it was just a few years ago. Several web sites already treat the subject of this writing, but because many are in the German language it is felt that another English write-up, albeit short in length, might be of interest to some readers.

Introduction
Observations were made several centuries ago that have to do with the effect of droplets of oil impinging onto an extended water surface, such as a lake or open sea. Depending on the nature of the oil, two conditions were observed. Either an apparent spreading of the oil over the surface was observed (as a calming of the water surface if it happened to be ruffled), or else a non-spreading of the oil resulted. Although it is known that wave damping has been observed through the centuries, it was not studied as a research project until the end of the 19th century by an 18 year-old young lady, a resident of Germany. The wave-reducing phenomenon was also observed during the 18th century by Benjamin Franklin. Some of his comments will be given below. In the English language, the phrase to "pour oil on troubled waters" has come to mean "to settle differences by calm, soothing methods" - the phrase probably originated from the effect mentioned.

Observations of Benjamin Franklin
On November 7, 1773 Franklin wrote a letter to one Doctor Brownrigg. Extracts of that letter are given below17.
"...I had, when a youth, read and smiled at PLINY'S account of a practice among the seamen of his time, to still the waves in a storm by pouring oil into the sea; which he mentions, as well as the use made of the oil by the divers...

"In 1757, being at sea in a fleet of 96 sail bound against Louisbourg, I observed the wakes of two of the ships to be remarkably smooth, while all the others were ruffled by the wind, which blew fresh. Being puzzled with the differing appearance, I at last pointed it out to our captain, and asked him the meaning of it? 'The cooks, says he, have, I suppose, been just emptying their greasy water through the scuppers, which has greased the sides of those ships a little;' and this answer he gave me with an air of some little contempt, as to a person ignorant of what every body else knew. In my own mind I at first slighted his solution, tho' I was not able to think of another. But recollecting what I had formerly read in PLINY, I resolved to make some experiment of the effect of oil on water, when I should have opportunity.

"Afterwards being again at sea in 1762, I first observed the wonderful quietness of oil on agitated water, in the swinging glass lamp I made to hang up in the cabin, as described in my printed papers, page 438 of the fourth edition. - This I was continually looking at and considering, as an appearance to me inexplicable. An old sea captain, then a passenger with me, thought little of it, supposing it an effect of the same kind with that of oil put on water to smooth it, which he said was a practice of the BERMUDIANS when they would strike fish, which they could not see, if the surface of the water was ruffled by the wind. This practice I had never before heard of, and was obliged to him for the information; tho' I thought him mistaken as to the sameness of the experiment, the operations being different; as well as the effects. In one case, the water is smooth till the oil is put on, and then become agitated. In the other it is agitated before the oil is applied, and then becomes smooth. - The same gentleman told me, he had heard it was a practice with the fishermen of LISBON when about to return into the river, (if they saw before them too great a surf upon the bar, which they apprehended might fill their boats in passing) to empty a bottle or two of oil into the sea, which would suppress the breakers, and allow them to pass safely: a confirmation of this I have not since had an opportunity of obtaining. But discoursing of it with another person, who had often been in the Mediterranean, I was informed that the divers there, who, when under water in their business, need light, which the curling of the surface interrupts by the refractions of so many little waves, let a small quantity of oil now and then out of their mouths, which rising to the surface smooths it, and permits the light to come down to them. - All these informations I at times revolved in my mind, and wondered to find no mention of them in our books of experimental philosophy.

"At length being at CLAPHAM where there is, on the common, a large pond, which I observed to be one day very rough with the wind, I fetched out a cruet of oil, and dropt a little of it on the water. I saw it spread itself with surprising swiftness upon the surface; but the effect of smoothing the waves was not produced; for I had applied it first on the leeward side of the pond, where the waves were the largest, and the wind drove my oil back upon the shore. I then went to the windward side, where they began to form; and there the oil, though not more than a teaspoonful, produced an instant calm over a space several yards square, which spread amazingly, and extending itself gradually till it reached the lee side, making all that quarter of the pond, perhaps half an acre, as smooth as a looking-glass.

"After this, I contrived to take with me, whenever I went into the country, a little oil in the upper hollow joint of my bamboo cane, with which I might repeat the experiment as opportunity should offer; and I found it constantly to succeed."

It should be mentioned that Franklin did not identify the type of oil used in his experiments. Not all oils would have worked. It is now known that those oils that have a polar group in its molecular structure (for example, a carboxyl group, COOH) would spread on the surface of water, with the nonpolar part of the molecule sticking out of the water. Long chain aliphatic molecules spread this way, whereas polymers form films where the molecules lie flat on the water surface. In all likelihood Franklin used olive oil in his experiments. Tanford said, on page 76 of his book35:
"Note on the word 'oil.' In Franklin's time the word 'oil,' without qualifying prefix, would have referred to oil used in the household, generally olive oil or sometimes fish oil or whale oil. Mineral oil (petroleum oil) had been known since antiquity, but saw little practical use until the nineteenth century. The distinction is important, because petroleum oil is pure hydrocarbon oil, and, ..., would not have produced the effects that Franklin observed."
Franklin went on to say:
"A gentleman from Rhode-island told me, it had been remarked that the harbour of Newport was ever smooth while any whaling vessels were in it; which probably arose from hence, that the blubber which they sometimes bring loose in the hold, or the leakage of their barrels, might afford some oil, to mix with that water, which from time to time they pump out to keep the vessel free, and that same oil might spread over the surface of the water in the harbour, and prevent the forming of any waves."
Benjamin Franklin (1706-1790) gave other examples of water calming with the use of oil; however, the spreading of oil on water required scientific study, which leads us to the story of a young German lady, which took place many years later.

The Groundbreaking Work of Agnes Pockels
Agnes Pockels

The secrets of nature are revealed to those who are observant and have an interest in understanding the phenomena in front of them. Some observations that involve water might be commonplace, but just why they happen is beyond elementary description. The skipping of stones on water is one that is easily executed, but much more difficult to explain or formulate. Capillarity is also commonly observed, but is difficult to explain in simple terms. Many persons, whose job it is to wash the dishes, probably have observed some rapid movement on the surface of the water but are unable to adequately describe what is being detected. Interest, close observation and sometimes mathematical formulation, are required to bring understanding to a subject. In this regard an advanced education is apt to help. In the subject to be discussed here, observations that undoubtedly many persons have made, were carried further than usual by a young lady to result in a whole new field of academic study - and the observations and experiments were made in an ordinary kitchen of the late nineteenth century.

The story begins on February 14, 1862, in Venice, Italy, when Agnes Luise Wilhelmine Pockels was born to Theodor and Alwine (nee Becker) Pockels32. Both parents were from northern Germany but Theodor was in the Royal Austrian Army at that time and was stationed in Italy. Due to poor health, Theodor Pockels retired from the army in 1871 and the family then moved northward; they settled in Braunschweig (Brunswick), Germany.

Agnes attended the local municipal school from 1872 to 1877. As was the custom at the time, girls did not enter the university for advanced education. After girls were allowed to enroll for higher education Agnes' parents would not allow it, so Agnes was destined to spent her life within the home, primarily to take care of family members, all of whom had physical problems.

Apparently Agnes was not one to complain, even though she had responsibilty for the everyday tasks that usually fall to the housewife. One of these tasks, of course, was to wash the meal dishes, which can be a mind-numbing chore for many persons. However, some persons to which that task falls will readily admit that there are some interesting phenomena to be observed if the dish-washing task can be done over an extended period of time. Soap bubbles can be entertaining for long periods, and they display colors that vary over time. It is also common to observe a rapid motion on the water surface when soap first comes in contact with the water. While the uninterested person may not comprehend the various observations, Agnes Pockels set her mind to understand the phenomena she observed on the water that was used for washing dishes.

Agnes Pockels apparently began to study the effects of substances on water in the year 1880, at age 18. She continued to work for several years until the year 1891 when she became aware of published articles by Lord Rayleigh (John William Strutt, 1842-1919) on a similar topic. As a worker in science, Agnes Pockels was quite isolated, so she decided to write to Lord Rayleigh to inform him of her experimental results. She wrote to Lord Rayleigh in the German language and he had his wife translate the German into English. Lord Rayleigh was duly impressed with the results and suggested that he submit her results to the publication Nature. This was done, and the following is a portion of the letter published on March 12, 1891:

"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 harmonizes with it. The later sections seem to me very suggestive, raising, if they do not fully answer, many important questions. I do hope soon to find opportunity for repeating some of Miss Pockels' experiments.
March 2-----Rayleigh"
The translated Pockel letter followed Rayleigh's letter. It had been written by Miss Pockels on January 10, 1891. It is the first reporting of her results.
"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.

"First, I will describe a simple method, which I have employed for several years, for increasing or diminishing the surface of a liquid in any proportion, by which its purity may be altered at pleasure.

"A rectangular tin trough, 70 cm. long, 5 cm. wide, 2 cm. high, is filled with water to the brim, and a strip of tin about 1 1/2 cm. wide laid across it perpendicular to its length, so that the under side of the strip is in contact with the surface of the water, and divides it into two halves. By shifting this partition to the right or left, the surface on either side can be lengthened or shortened in any proportion, and the amount of the displacement may be read off on a scale held along the front of the trough."

The letter was quite long and it detailed results of Miss Pockels' experiments. It might be noted here that years later Irving Langmuir studied films on water and used a trough similar to that designed by Miss Pockels. Today (2006) the trough used in surface science studies is referred to as the "Langmuir trough". The original idea for the trough in such studies did, of course, originate with Miss Pockels.

In total, Agnes Pockels published sixteen articles regarding her work. Her articles dealt with the tin water trough, horizontal balance, surface tension, contact angles, effect of contamination on the water surface, thickness of monolayers on water, properties of surfactants and surface tension of liquid solutions - certainly a very big step into the new field of surface science.

There is a proverb that states, "curiosity killed the cat." This is simply a warning that if one is too inquisitive, harm might come to that person. That certainly might be true in the case of a cat, but curiosity is a required characteristic of a person if she (or he) is to understand physical and chemical phenomena - and it is this characteristic that Agnes Pockels must have had in full measure. For at least ten years she experimented and collected data before contacting Lord Rayleigh, and in so doing, formed the foundation of a new scientific field. While mainline researchers usually have doctorate degrees, Miss Pockels did not have a formal education after age fifteen! Of course, this must have been a handicap for her, especially with a lack of knowledge of higher mathematics.

While carrying out her household chores, Miss Pockels continued doing research and publishing articles. However, there were periods of time when research was not possible as her own failing health and eyesight were obstacles that could not be overcome easily. However, she persisted, and on her 70th birthday an article was published by Wolfgang Ostwald18 in tribute to her work. In addition, Miss Pockels was awarded an honorary doctorate from the Technical University Carolo-Wilhelmina in Brunswick in 1932. Another recognition was made by Sir William Bate Hardy19:

"In the late 'nineties a most ingenious method of demonstrating the existence of films on water, and of controlling them for experimental purposes, was devised by a German lady, Fräulein Pockels. I think I may say without exaggeration that the immense advances in the knowledge of the structure and properties of this fourth state of matter which have been made during this century are based upon the simple experimental principles introduced by Miss Pockels."
Thus, household chores and caring for sick members of her family did not prevent Agnes Pockels from achieving international recognition. Much of it, unfortunately, came after her death.

Agnes Pockels passed away on November 21, 1935.

Events in the Life of Agnes Pockels
Year - Age - Event
1862 - 0 - born in Venice, Italy
1865 - 3 - brother Friedrich born
1871 - 9 - moved to Braunschweig (Brunswick), Germany
(1872-1877) - (10-15) - attendance at the Municipal Girl's School
1880 - 18 - discovery of the anomalous state of the water surface
1882 - 20 - development of the slide trough for water surface studies
1891 - 29 - correspondence with Lord Rayleigh (1842-1919); first publication of the results of her work (in Nature)
(1892-1899) - (30-37) - six articles published during this period
1900 - 38 - marriage of brother Friedrich to Elisabeth Hartig
1902 - 40 - translation into German, from the English, of George Howard Darwin's book on tides.
1906 - 44 - death of her father, Theodor (1830-1906)
1907 - 45 - Miss Pockels no longer entered information into her diary
1913 - 51 - death of her brother, Prof. Dr. Friedrich Pockels (1865-1913)
1914 - 52 - death of her mother, Alwine (1838-1914)
1932 - 70 - recipient: Laura-Leonard Prize for 1931; honorary doctorate from Carolina-Wilhemina University of Brunswick; tribute by Wolfgang Ostwald
1933 - 71 - publication of 16th and last article
1935 - 73 - death of Agnes Pockels

Agnes Pockels, later in life

Epilogue
There are some excellent write-ups on the subject of Agnes Pockels that have been reported in scientific journals. For a more in-depth treatment of this subject the writer suggests the articles by Giles and Forrester23, Eleanor S. Elder26, Gabriele Beisswanger29, M. Elizabeth Derrick30 and Liane Biermann31.

One of the film-forming fatty acids Miss Pockels used on the water surface was stearic acid. This particular substance is one that was used later by Irving Langmuir and Katharine B. Blodgett in their work. For his work in surface science, Langmuir was presented with the Nobel Prize in Chemistry in 1932; in one of his articles he gave recognition to Miss Pockels and her work.

Miss Blodgett developed a step gauge for determining the thickness of a thin film by matching colors. Examples of built-up films of barium-copper stearate on chromium-plated glass slides are shown below.

From left to right, the number of barium-copper stearate double layers (49.50Å per double layer) on the slides are: At left: 19, 61, 105, 148, 191, 234. Second from left: 18, 38, 61, 80, 105, 123, 148, 164, 191, 206, 234, 247. Second from right: 61, 80. At right: 35-55. The least number of layers is toward the top of the slide in this view.

Acknowledgements
The writer is most appreciative of the articles and comments contributed by Dr. Dieter Leseberg of the Technical University Braunschweig, Braunschweig, Germany. Many technical articles were generously supplied by Ohio University in Athens, Ohio, U.S.A. The image of Miss Pockels at an early age was downloaded from Reference 37; the image of Miss Pockels later in life was downloaded from Reference 36. The use of these high quality images is very much appreciated. Last, but not least, my thanks go to Hans-Christian Rohde for obtaining a copy of one of the obscure articles for me.

Articles by Agnes Pockels
1) Lord Rayleigh, "Surface Tension," Nature, Vol XLIII, 1891, pp 437-439. The majority of this article consists of a letter, translated from German to English, which was written by Miss Pockels to Lord Rayleigh.
2) Agnes Pockels, "On the Relative Contamination of the Water-Surface by Equal Quantities of Different Substances," Nature, Vol 46, No 1192, Sep 1, 1892, pp 418-419.
3) Agnes Pockels, "Relations Between the Surface-Tension and Relative Contamination of Water Surfaces," Nature, Vol 48, Jun 15, 1893, pp 152-154.
4) Agnes Pockels, "On the Spreading of Oil upon Water," Nature, Vol 50, 1894, pp 223-224.
5) Agnes Pockels, "Beobachtungen über die Adhäsion verschiedener Flüssigkeiten an Glas" (Observations on the Adhesion of Different Liquids on Glass), Naturwissenschaftliche Rundschau, Vol 13, 1898, pp 190-191.
6) Agnes Pockels, "Untersuchung von Grenzflächenspannungen mit der Cohäsionswaage" (Investigations of the Surface Tension with the Cohesion Balance), Annalen der Physik, Vol 67, 1899, pp 668-681.
7) Agnes Pockels, "Randwinkel gesättigter Lösungen an Krystallen" (Contact Angles of Saturated Solutions on Crystals), Naturwissenschaftliche Rundschau, Vol 14, No 30, 1899, pg 383.
8) Agnes Pockels, "Ueber 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), Annalen der Physik, Vol 8, 1902, pp 854-871.
9) Agnes Pockels, "Das Willkürliche in der Welt," Annalen der Naturphilosophie, Vol 8, 1909, pp 321-328.
10) Agnes Pockels, "Über Randwinkel und Ausbreitung von Flüssigkeiten auf festen Körpern" (On Contact Angles and the Flow of Fluids on Solid Bodies), Physikalische Zeitscrift, Vol 15, 1914, pp 39-46.
11) Agnes Pockels, "Über die Ausbreitung reiner und gemischter Flüssigkeiten auf Wasser" (On the Spreading of Pure and Mixed Liquids on Water), Physikalische Zeitschrift, Vol 17, 1916, pp 142-145.
12) Agnes Pockels, "Zur Frage der zeitlichen Veränderung der Oberflächenspannung" (On the Changes of the Surface Tension with Time), Physikalische Zeitschrift, Vol 17, 1916, pp 441-442.
13) Agnes Pockels, "Die Anomalie der Wasseroberfläche" (The Anomalous State of the Water Surface), Naturwissenschaften, Vol 5, 1917, pp 137-140, 149-153.
14) Agnes Pockels, "Zur Frage der Ölflecke auf Seen" (On Oil Patches on Lakes), Naturwissenschaften, Vol 6, 1918, pg 118.
15) Agnes Pockels, "The Measurement of Surface Tension with the Balance," Science, Vol 64, No 1656, 1926, pg 304.
16) Agnes Pockels, "Über die Abhängigkeit der Benetzbarkeit fester Körper von der Berührungsdauer," Kolloid-Zeitschrift, Vol 62, No 1, Jan 1933, pp 1-2.

It should be pointed out that Miss Pockels had an excellent grasp of the English language. In addition to writing some articles in English, she undertook the translation of a book written by George Howard Darwin, in the English language, on the subject of tides. That translation into the German language was printed in the year 1902. The title became Ebbe und Flut - Sowie Verwandte Erscheinungen im Sonnensystem.

References and Bibliography
17) "Of the Stilling of Waves by Means of Oil." Extracted from sundry letters between Benjamin Franklin, William Brownrigg and the Reverend Mr. Farish. Extract of a Letter from Doctor Brownrigg to Dr. Franklin dated Jan 27, 1773, Philosophical Transactions of the Royal Society of London, Vol 64, 1774, pp 445-447. Extract of a Letter to Doctor Brownrigg from Doctor Franklin dated Nov 7, 1773, Philosophical Transactions of the Royal Society of London, Vol 64, 1774, pp 447-460.
18) Wolfgang Ostwald, "Die Arbeiten von Agnes Pockels über Grenzschichten und Filme," Kolloid-Zeitscrift, Vol 58, No 1, Jan 1932, pp 1-8.
19) William Bate Hardy, Collected Scientific Papers of Sir William Bate Hardy, Cambridge University Press, 1936,
pp 738-742.
20) Elisabeth Pockels, "Ein gelehrtes Geschwisterpaar - Zur Erinnerung an Agnes Pockels (1862-1935)," Bericht der Oberhessischen Gesellschaft für Natur-und Heilkunde zu Giessen, Vol 24, 1949, pp 303-307; written in 1944.
21) C. H. Giles, "Franklin's Teaspoonful of Oil -Studies in the Early History of Surface Chemistry, Part 1," Chemistry and Industry, Nov 8, 1969, pp 1616-1624.
22) C. H. Giles and S. D. Forrester, "Wave Damping: The Scottish Contribution - Studies in the Early History of Surface Chemistry, Part 2," Chemistry and Industry, Jan 17, 1970, pp 80-87.
23) 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, No 2, January 9, 1971, pp 43-53.
24) Stanley D. Forrester and Charles H. Giles, "Rayleigh and the Great Monolayer Discovery - Centenary of a Landmark in Chemistry," Chemistry and Industry, July 21, 1979, pp 469-474.
25) M. Elizabeth Derrick, "Agnes Pockels, 1862-1935," Journal of Chemical Education, Vol 59, Dec 1982, pp 1030-1031.
26) Eleanor S. Elder, "Agnes Pockels - Indeed a Lady," Chemistry, Vol 47, No 1, Jan 1974, pp 10-12.
27) C. H. Giles und S. D. Forrester, "Agnes Pockels und die Urspünge der Oberflächenchemie" (Agnes Pockels and the Origin of Surface Chemistry), Mitteilungen der Technischen zu Braunschweig, Vol 13, 1978, pp 15-28.
28) Ronald W. Clark, Benjamin Franklin - A Biography, Random House, New York, 1983, pp 136-137.
29) Gabriele Beisswanger, "Das Portrait: Agnes Pockels (1862-1935) und die Oberflächenchemie" (The Portrait: Agnes Pockels (1862-1935) and Surface Chemistry), Chemie in unserer Zeit, Vol 25, No. 2, 1991, pp 97-101.
30) M. Elizabeth Derrick, "Agnes Pockels (1862-1935," Women in Chemistry and Physics - A Biobibliographic Sourcebook, Edited by Louise S. Grinstein, Rose K. Rose, and Miriam H. Rafailovich, Greenwood Press, Westport, Connecticut, 1993, pp 502-507.
31) Liane Biermann, "Agnes Pockels: 1862 - 1935," Broschüre der Presse- und Öffentlichkeitsarbeit der TU Braunschweig,
ca 1998.
32) Gabriele Beisswanger, "Agnes Luise Wilhelmine Pockels," Neue Deutsche Biographie, Duncker & Humblot, Berlin, Vol 20, 2001, pg 555.
33) Andrea Kruse and Sonja Schwarzl, "Zum Beispiel: Agnes Pockels," Nachrichten aus der Chemie, Jun 2002, pp 759-760.
34) Seymour Stanton Block, Benjamin Franklin, Genius of Kites, Flights and Voting Rights, Chapter 8, "Detergents, Emulsions, and Foams," McFarland & Company, Inc., Publishers, Jefferson, North Carolina, 2004, pp 178-206.
35) Charles Tanford, Ben Franklin Stilled the Waves, Oxford University Press, Oxford, England, 2004.
36) Christiane A. Helm, "Agnes Pockels: Life, Letters and Papers," March 23, 2004, Forum on the History of Physics, APS.
37) CWP at UCLA (Contributions of 20th Century Women to Physics).