11 ms·
In 1870, Lord Rayleigh used oil and water to calculate the size of molecules
- rkagerer 2y agoFun fact: Every 4 days humanity produces enough oil to cover the entirety of the world's oceans. Source: Public statistics and my back-of-napkin math, not accounting for waves.
- Marvinkw 2y ago[dead]
- ForOldHack 2y agoHe had time to think. Something so rare these days. 30 years later, Henry Cavendish measured G and estimated the density of the earth. Using candles, mirrors and telescopes. https://en.wikipedia.org/wiki/Cavendish_experiment https://en.wikipedia.org/wiki/Cavendish_experiment
- rendall 2y agoWe performed this experiment in high school chemistry and it has remained with me as one of my deepest aha moments. It has become fashionable in foodie circles to mock the idea of adding oil to boiling pasta so as to prevent stickiness. The argument against seems to be that oil floats and cannot possibly affect the pasta, unless you add so much that the pasta becomes slimy. But I maintain that a drop of two in boiling water is enough to coat all the pasta in a single layer of molecules. The agitation of the water spreads the oil evenly as a kind of colloidal suspension. All these fancy restaurants with elaborate methods to avoid sticky pasta.
- hn_throwaway_99 2y agoI love articles like this. I feel like too often in science education (at least my science education) that laws and theories are presented as just something that you need to memorize, when in my opinion the stories of how things were originally discovered and figured out is eminently more fascinating and inspiring. Like I remember having to learn all of these biochemical pathways, but I left school with nary a clue as to how these pathways were uncovered in the first place. Thanks for submitting! Would welcome suggestions for any other publications on how scientific theories were first discovered.
- stevenwoo 2y agoDid you get your physics education in high school or university? I only had to take one physics class in the USA at college for my major, quantum electrodynamics for electrical engineering but my professor wrote the textbook and I recall he went over each experiment starting from the fundamentals of our understanding of the basics of the atom, Newton's understanding of light at the time, double slit experiment, to Maxwell's equations, the Michelson Morley ether experiment, to deriving then proving experimentally proving general relativity and decomposing GR into Newtonian physics/other laws of electromagnetism, I am still in awe at the people just figuring this stuff out from first principles. Anyways, I haven't read this (have it on hold at my library) but someone recommended this book on reddit How to Make an Apple Pie from Scratch: In Search of the Recipe for Our Universe, from the Origins of Atoms to the Big Bang https://www.publishersweekly.com/9780385545655 https://www.publishersweekly.com/9780385545655
- layer8 2y ago> experimentally proving general relativity Can you elaborate on that? What experiments did the professor perform?
- stevenwoo 2y agoI mis wrote, he talked about the experiments done to verify general and special relativity. Michelson-Morley was one of them that sticks in my mind along with some traveling atomic clocks. We never recreated the experiments like some of the other commenters did in their classes.
- augustusseizure 2y agoWhat’s the name of that textbook? It sounds really interesting. Isaac Asimov wrote a couple books that follow the narrative of science from the beginnings up until the 80s or so, which I highly recommend. One is called Atom and is more focused on how we got to our “present” understanding of particles. There’s also one that takes a broader view, it’s something like History of Science (? not at my bookshelf right now). There’s several books in this genre for math as well. IMO it’s a much better structure for pedagogy since we can piggy back the education on our natural wiring to care about narrative and mystery/puzzles.
- nick238 2y agoThe page is timing out for me, but is it the inverse problem of the time when Steve Mould/Matt Parker measured the unknown quantity π, but already assuming a size of the molecules? Presumably Lord Rayleigh already had a at least a good order-of-magnitude approximation of pi... https://www.youtube.com/watch?v=lmgCgzjlWO4 https://www.youtube.com/watch?v=lmgCgzjlWO4
- thirdhaf 2y agoBy 1870 pi was known to several hundred decimal digits, for something like this calculation where you have other large sources of error Archimedes approximation from 2 millennia earlier would probably be fine. (<1% error) https://en.m.wikipedia.org/wiki/Chronology_of_computation_of_%CF%80 https://en.m.wikipedia.org/wiki/Chronology_of_computation_of...
- jjk166 2y agoNote that pi to 40 digits is sufficient to calculate the circumference of the observable universe to subatomic precision.
- bqmjjx0kac 2y ago> Assuming that the oil formed a single layer of molecules — a monolayer — then the thickness of the oil film is the same thing as the length of one oil molecule. How did he know that the film of oil was one molecule thick? It feels like a huge assumption to me, but maybe this blog post left something out.
- deleted 2y ago[deleted]
- cb321 2y agoThe molecular scale was well estimated (at least for the gaseous phase of matter) by 1865 (25 years earlier not 5 as the incorrect HN title would suggest) https://physics.stackexchange.com/questions/13757/how-was-avogadros-number-first-determined https://physics.stackexchange.com/questions/13757/how-was-av... (and guesstimated by just "following your nose" in Gandalf-of-Lord-Of-The-Rings-ese in 1646!) Rayleigh's experiment is just accessible requiring very little training / background to describe. To interpret as a monolayer is honestly probably not so accessible at all, though, and a weakness of the atomsonly.news piece and seemingly not even done by Rayleigh himself. Modern retconning as zokier says elsewhere.
- munchler 2y agoAgreed. The experiment actually gives an upper limit on the size of a molecule in one particular dimension. Still a very useful result.
- bangonkeyboard 2y agoI would have loved to have had a course in school about "The Design of Scientific Experiments." One that described the processes of landmark historical experiments from antiquity onward, and challenged students throughout: "Given this set of constraints, how would you design and execute an experiment to estimate the size of the Earth? Disprove phlogiston and luminiferous aether? Measure the speed of light?"
- dekhn 2y agoI don't think many people today would be able to propose the Michelson Morley experiment and then actually do it. It was truly heoric (and Michelson was a genius). We did this oil/water experiment in freshman physics or chemistry lab. It was rushed, everybody just did the minimum, the teachers barely explained any of it, and then we moved on.
- _dark_matter_ 2y agoI agree. The Michelson Morley experiment reminds me of some difficult algorithms: simple only in hindsight, and implementation is _hard_ to do correctly.
- buescher 2y agoPeople still win Nobel prizes (LIGO, for example) using interferometers. It’s arguably the single greatest invention in experimental physics.
- bsder 2y agoExperiments are HARD. There is a joke among physicists that theoreticians are washed up by 35 but experimentalists don't even get started until 45. To make a physics experiment work you have to be ridiculous about recording details and have a strong intuition. You have to design the experiment such that you can differentiate between "hypothesis wrong" and "equipment doesn't work" because you don't know the answer. (For example: When they turned on LIGO for the first time, they almost immediately caught a great event. Huge victory party, right? Nope. They promptly ignored it assuming that something was wrong with the machine. And it was only after significant post analysis and correlation that they decided that it was a real event.)
- CountHackulus 2y agoWe recreated this experiment in one of my university physics classes. It was a lot of work, and our results weren't nearly as good, but it was instructive and interesting. The equipment requirements were completely reasonable for an undergrad physics lab. I highly recommend giving it a try if you can.
- metadat 2y agoHow is the measurement for the area the oil has spread over performed? Visually or some other way?
- opencl 2y agoThe actual manuscript from Rayleigh [1] explains it better: the area is the entire area of the vessel the oil was placed in, and the thing actually being measured was how much oil was required for it cover the whole area. [1] https://www.damtp.cam.ac.uk/user/gold/pdfs/teaching/old_literature/Rayleigh1890.pdf https://www.damtp.cam.ac.uk/user/gold/pdfs/teaching/old_lite...
- dekhn 2y agoSome powder is added to the water, which covers the surface of the water but not the oil patch (which is circular). Then the oil patch diameter is measured.
- misnome 2y agoThis was how we did this when we replicated this experiment in high school. I guess from the other responses here that this wasn't common?
- dekhn 2y agoThe original way was to cover the surface of a round bowl with oil. It certainly makes a lot more sense to me than trying to measure a floating disk of oil.
- wa2flq 2y agoWhen we did it in high school (70's) we just used compound that had a long chain (soap?) and only one end dissolved in the water. It was very easy to measure and calculate the size of the molecule . We had a series of these simple experiments. Another I recall was measure the speed at which certain volatile compounds moved through the air. I definitely learned that all science doesn't have to involve complex equipment.
- 2y ago
- alnwlsn 2y agoThese are the best kind of posts, where there's something I've never even heard of before. I never knew 'oiling the seas' was a thing, or that it (apparently?) works.
- dr_dshiv 2y agoI won’t trust this until I myself can calm an acre of water with a teaspoon of oil. (Or at least see a YouTube video of someone doing it)
- isp 2y agoYouTube video: https://www.youtube.com/watch?v=RST_ylwVrUw&t=1m27s https://www.youtube.com/watch?v=RST_ylwVrUw&t=1m27s
- shortstuffsushi 2y agoThat's funny, thanks for sharing. I was watching his video where he's saying "you can see it right there, look how much calmer it is, it looks like ice" and was thinking "I don't know what he's talking about I don't see ... oh, that ice patch is water"
- eesmith 2y agoAnother version is in Phil Morrison's "The Ring of Truth" episode "Atoms" at https://youtu.be/WQ3mjb9BSaU?t=1765 https://youtu.be/WQ3mjb9BSaU?t=1765 or 29:26 at https://archive.org/details/TheRingofTruth/Ring.of.Truth.S01E05.Atoms.1987.VHSRip.AAC2.0.x264-rattera.mp4 https://archive.org/details/TheRingofTruth/Ring.of.Truth.S01... . (It would be nice if archive.org had a way to link to a specific timestamp.)
- Terr_ 2y agoThat reminds me of the Millikan & Fletcher oil-drop experiment [0], which measured the charge of the electron. In short, microscopic atomized oil droplets had their fall-time through air measured to figure out their volume, and then a known electric field was used to levitate them. The calculated charge-per-molecule clustered around multiples of a smaller value, which would be the charge of an individual electron. [0] https://en.wikipedia.org/wiki/Oil_drop_experiment https://en.wikipedia.org/wiki/Oil_drop_experiment
- n_plus_1_acc 2y agoHow can you make sure you don't end up with 2e as a result? (Or any other multiple)
- Terr_ 2y agoIn 1909 the results results were couched in some "elementary electric charge" quantity, since the now-familiar subatomic particle model (and the "electron") was still gaining acceptance. I expect that the greater the number of trials, it becomes easier it is to detect a distinction between closer-multiples, and if at some point more trials stops changing the answer then you've likely converged on e, unless there's some new principle like "X-ray exposure only affects charge in in multiples of e greater than one."
- adrian_b 2y agoThe approximate value of the elementary electric charge had been known since 1874, when it was first computed by George Johnstone Stoney. After Stoney, other experiments had reduced the uncertainty with which the value was known, but it remained relatively high. The importance of the experiments of Robert Andrews Millikan consists in the fact that the uncertainty of the value of the elementary electric charge obtained by this method was much smaller than by any previous method (he claimed that it was better than one half of one percent, but he used wrong values for the viscosity of air, so his actual result was off by more than that, but still by less than one percent from the correct result).
- 2y ago
- xenocratus 2y agoLuckily it wasn't my grade that got this experiment as the practical exam in one of the National Physics Olympiads I went to... :) poor souls, most got answers orders of magnitude away.
- IncreasePosts 2y agoA few days ago, there was a HN post about surface acoustic wave filters, and a commenter mentions how inspired the inventor of it must have been(https://news.ycombinator.com/item?id=41604937 https://news.ycombinator.com/item?id=41604937). That was this same fella!
- coldcache 2y agoRelated: Agnes Pockels’ experiments [0] [0]: https://en.wikipedia.org/wiki/Agnes_Pockels https://en.wikipedia.org/wiki/Agnes_Pockels
- carlob 2y agoTen years earlier and she didn't publish it right away. That really goes to show how much more difficult it was for a woman to become a scientist back then.
- RachelF 2y agoSemi off topic: Interesting to look at picture of the text of the 1890 paper. That typesetting is almost the same as modern scientific papers. Maybe Rayleigh had an early copy of LaTeX? ;-)
- buescher 2y agoThank Knuth for TeX or good scientific typesetting would be a nice thing the Victorians had.
- wwarner 2y agoIn 1676 Roemer estimated the speed of light by timing the orbit of Jupiter’s moon Io, noting that as the Earth approached Jupiter, Io emerged from behind Jupiter a little earlier every day, and as the Earth traveled away from Jupiter it appeared a little later every day, with the time of day varying by 22 minutes over a year. Knowing the difference between the two distances, he reckoned that light travels that distance in 22 minutes, or 227 thousand km/s. The actual speed is about 300 thousand km/s. Not bad!
- ForOldHack 2y agoThe speed of light, because it is so fast, is the most precise physical constant known : 299 792 458 m / s. Less than 7/1000ths away from 300,000,000 m / s. I am not going to sweat this in the least. So light travels only 0.3 m / nano second, or 11.802 inches. https://www.youtube.com/watch?v=9eyFDBPk4Yw https://www.youtube.com/watch?v=9eyFDBPk4Yw
- Neikius 2y agoArmed with this fact thinking about electronic devices. How the front of the signal travels and how suddenly the distance matters. Was blown away when I first thought about this.
- glial 2y agoTherefore in one cycle of a 3GHz processor, light travels about 4 inches. Wild.
- xhrpost 2y agoWhich is maybe part of the reason RAM needs to be so close to the CPU? Granted though most RAM access takes several CPU cycles.
- fennecfoxy 2y agoThis is exactly it, the longer your traces (or any sort of write I guess) between processor and memory, the longer delay you have to have for things to "settle". Additionally increasing capacitance means that it takes more effort (read, even longer) for the line to settle. Does make me realise I don't know so much about the super low level parts of it beyond electrons and holes. One end of the wire needs to be at a lower potential to encourage electrons to flow from that side to the other. Hmmm.
- thimkerbell 2y ago"Rayleigh divided the volume of the oil by the area it covered, thus estimating the thickness of the oil film. Assuming that the oil formed a single layer of molecules — a monolayer — then the thickness of the oil film is the same thing as the length of one oil molecule. This is how Lord Rayleigh became the first person to figure out a single molecule’s dimensions, many years before anyone could see such molecules."
- pechay 2y agoWe did this same experiment in school, with a tiny pinprick of oil, estimating the volume of the drop as a sphere, and a small water tank, and then estimated the area of oil slick as a circle.
- nmstoker 2y agoYes, we did it in physics at school too, when we were 13 or 14 I think.
- FredPret 2y agoVery cool. For more like this, check out this lecture series: https://www.thegreatcoursesplus.com/the-evidence-for-modern-physics-how-we-know-what-we-know https://www.thegreatcoursesplus.com/the-evidence-for-modern-... It's by a guy called Don Lincoln and it's about how we established things like the existence of atoms, the speed of light, and many other fundamental things that are good to know. It's also an audiobook, though the lectures are easier to follow.
- dilawar 2y agoI went to a talk by a very old physicist. At the end of his talk, he said, recalling from memory, all of the great experiments of the past were done by nothing. If an experiment costs more than $100, I am out. His setup has mud in a jar and bacteria in it which you can see with a simple microscope or handheld lens.
- AlotOfReading 2y agoThat's a bit harsh. To give one counterexample, the Michelson-morley experiment put the figurative nail in the coffin of centuries of speculation about the "luminiferous aether". The experimental apparatus was a table-sized precision carved slab of sandstone floating in a huge vat of mercury, holding the highest precision optical equipment of the day. I suspect it cost rather more than $100 even in the 1880s.
- veltas 2y agoAlthough it was a refinement of the Fizeau experiment which conceivably could have cost $100 in living memory.
- 00_hum 2y ago[dead]
- ziofill 2y ago>"not more than a Tea Spoonful," according to his diary — Franklin poured it onto the agitated water. The oil spread rapidly across the surface, covering "perhaps half an Acre" of the pond and rendering its waters "as smooth as a Looking Glass." What??
- imp0cat 2y agoHere's a video from another post: https://news.ycombinator.com/item?id=41630637 https://news.ycombinator.com/item?id=41630637
- Summerbud 2y ago> I love this story because it shows, at least anecdotally, how deep scientific insights can emerge from the simplest of experiments. It's a testament to the idea that you don't always need sophisticated equipment to unlock the secrets of nature — sometimes, all it takes is a drop of oil and a bit of ingenuity. This can apply to many other fields too!
- quantadev 2y agoThe credit for proving the existence of atoms is more often associated with Einstein's explanation of Brownian motion and Jean Perrin's experimental confirmation, even though earlier work by Lord Rayleigh, Benjamin Franklin, and others hinted at the molecular structure of matter.
- cwillu 2y agoSite has gone down with a dns error of some kind; anyone have a snapshot?
- nes350 2y agohttps://archive.is/oMgPW https://archive.is/oMgPW (The domain of the original article seems to be dead)
- rkagerer 2y agoThis is fascinating, but wasn't it still a bit of a conjecture to assume the oil would spread to a minimum thickness of one molecule? Did he have any doubts, like that surface tension might keep it thicker? Or other clues hinting it was indeed a monolayer?
- zestyping 2y agoTo me, the much more questionable assumption is that volume is preserved when a liquid spreads out to a layer one molecule thick. There's no reason why the volume you get when each oil molecule is surrounded on all sides by other oil molecules should be the same as when each oil molecule has air above and water below. Can anyone explain why this is so?
- nielsbot 2y agoMy question exactly.. I hope someone can chime in :) EDIT: Thinking a bit more... I suppose it's a reasonable assumption that the molecules (mostly) wouldn't stack on top of each other. They all want to get lower and perhaps the resistance to the oil spreading out is much lower proportionately that the gravitational force encouraging the oil to flatten
- lIl-IIIl 2y agoBut if I spill some oil on my plate it doesn't look a molecule thin to me. Why is it different with water?
- zokier 2y agoI believe this is at least part of the explanation. Although there might have been some further developments in the 100 years since this was published Oleic acid on water forms a film one molecule deep, in which the hydrocarbon chains stand vertically on the water surface with the COOH groups in contact with the water. Acetic acid is readily soluble in water because the COOH group has a strong secondary valence by which it combines with water. Oleic acid is not soluble because the affinity of the hydrocarbon chains for water is less than their affinity for each other. When oleic acid is placed on water the acid spreads upon the water because by so doing the COOH can dissolve in the water without separating the hydrocarbon chains from each other. When the surface on which the acid spreads is sufficiently large the double bond in the hydrocarbon chain is also drawn down on to the water surface, so that the area occupied is much greater than in the case of the saturated fatty acids. Oils which do not contain active groups, as for example pure paraffin oil, do not spread upon the surface of water https://zenodo.org/records/1429064 https://zenodo.org/records/1429064
- tony-allan 2y agohttps://www.atomsonly.news/p/franklin-oil https://www.atomsonly.news/p/franklin-oil Why this domain has been suspended Since January 2014, all ICANN accredited registrars (like Namecheap) have been required to verify the contact information (Registrant Whois) of customers registering domain names. This includes modifications to the contact details.
- tony-allan 2y agoFixed!
- cchi_co 2y agoEven back in the day, without all our modern technology, great minds like Franklin and Rayleigh could uncover truths that still resonate today.
- donkeybeer 2y agoIts not ancient times, some of the most accurate measuring instruments of that time are of a precision that you'd still need a few hundred or thousand dollars to buy today. The tooling wasn't primitive by any means.
- adrian_b 2y agoThe title of this thread appears to be wrong, because the parent article says "But a little experiment that Rayleigh performed in 1890, inspired directly by Franklin's observations, is not nearly as well-known." Therefore Rayleigh computed the size of molecules in 1890, not in 1870 (in 1870 Rayleigh was young and not known yet for any original research). While Rayleigh has devised a novel method for determining the size of molecules, it should be noted that the first who has succeeded to determine the size and weight of molecules was Johann Josef Loschmidt, in 1865. https://en.wikipedia.org/wiki/Johann_Josef_Loschmidt https://en.wikipedia.org/wiki/Johann_Josef_Loschmidt The publication of the weight and size of air molecules by Loschmidt is one of the most important milestones in the history of physics. Until that moment in 1865, the theory of atoms revived by Dalton could still be considered as some kind of fictitious model that explained some features of the chemical reactions and of thermodynamics, but which might have been wrong and which would probably be replaced by some better model. Starting from that moment, the atoms and molecules could be weighed and counted, so their reality was no longer questioned. The determination by Loschmidt of the size and weight of air molecules was enough to determine the sizes and weights of any other known atoms and molecules, making use of the relative atomic weights that could be determined from chemical reactions and which were already known. Moreover, a few years later, in 1874, George Johnstone Stoney has used the results of Loschmidt together with the theory of the existence of an elementary electric charge published by Maxwell one year before, in 1873, to compute the value of the elementary electric charge. Some years later, Stoney has given the name "electron" to the elementary electric charge, which has been the source of a very large number of words in modern science and technology, from electronics to hadrons.
- OvbiousError 2y agoCool article. They somehow got the formula wrong though, the formula on the screenshot has an additional factor of 0.9 that accounts for the fact that 1l of oil is not 1 kg. Perhaps it's intentional, but for something so simple I don't think it needs to be dumbed down even further.
- jll29 2y agoThanks for covering that story - I lived at Clapham Common for seven happy years. So much history: there is also a little church on the Common, whose past members played a role in the abolishion of slavery: https://en.wikipedia.org/wiki/Clapham_Sect https://en.wikipedia.org/wiki/Clapham_Sect
- kitd 2y ago> and he charted the Gulf Stream’s course across the Atlantic ocean, noting that ships traveling from America to England took longer than those going the opposite direction ?? Has the Gulfstream changed direction in the intervening years?
- kopirgan 2y agoVery interesting indeed! Was he just lucky that the spread was 1 molecule thick or that's the way oil spreads on water? Why?
- yapyap 2y agowow, he really had some knowledge for a lord