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In 1870, Lord Rayleigh used oil and water to calculate the size of molecules

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Re: In 1870, Lord Rayleigh used oil and water to calculate the size of molecules

#91

Post by Cheer2171 »

komali2 wrote: post #81
happytoexplain wrote: post #13

Earlier quoted context omitted.

It feels intuitive that a thin fluid on a low-friction surface (like water) would spread out "as much as possible" given enough time. There certainly may be confounding factors, but it seems like a reasonable thing to pin as an "assumption" in a hypothesis. I.e. he didn't have to "know" - assumptions are OK, and I don't feel like this one is huge .

I'm confused, the blog wrote "known amount of water," so was it a closed little area like a bathtub? If you added a ton of oil wouldn't it spread out as much as possible aka 600 molecules thick or whatever? Or did he pour it into a huge lake or something?

One drop in a soup bowl sized petri dish, measure the area it covers.

Re: In 1870, Lord Rayleigh used oil and water to calculate the size of molecules

#92

Post by tony-allan »

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.

Re: In 1870, Lord Rayleigh used oil and water to calculate the size of molecules

#94

Post by eesmith »

isp wrote: post #30
dr_dshiv wrote: post #14

I 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)

YouTube video: https://www.youtube.com/watch?v=RST_ylwVrUw&t=1m27s

Another version is in Phil Morrison's "The Ring of Truth" episode "Atoms" at https://youtu.be/WQ3mjb9BSaU?t=1765 or 29:26 at 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.)

Re: In 1870, Lord Rayleigh used oil and water to calculate the size of molecules

#95

Post by pdm55 »

Terr_ wrote: post #15

That 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…

There is always more to the story:

https://www.scribd.com/document/661270387/My-Work-with-Milli... Fletcher & Millikan

https://www.youtube.com/watch?v=B-uWaEvXqbA

Re: In 1870, Lord Rayleigh used oil and water to calculate the size of molecules

#96

Post by lern_too_spel »

hn_throwaway_99 wrote: post #2

I 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 a…

How we derived the laws and theories is science. (Some of the other commenters are mixing this together with biographies of the scientists, which is not science but is sometimes interesting in its own right.) The laws and theories in isolation are just trivia, and any class that teaches just those cannot truthfully be called a science class. Demand a better education.

Re: In 1870, Lord Rayleigh used oil and water to calculate the size of molecules

#97

Post by jonny_eh »

RheingoldRiver wrote: post #83
hn_throwaway_99 wrote: post #2

I 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 a…

I highly recommend this book! https://www.goodreads.com/book/show/25238350-the-hunt-for-vu...

I'd recommend this one instead: https://en.wikipedia.org/wiki/A_Short_History_of_Nearly_Ever...

Re: In 1870, Lord Rayleigh used oil and water to calculate the size of molecules

#98

Post by AlotOfReading »

dilawar wrote: post #65

I 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.

That'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.

Re: In 1870, Lord Rayleigh used oil and water to calculate the size of molecules

#99

Post by nielsbot »

rkagerer wrote: post #89

This 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?

My 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

Re: In 1870, Lord Rayleigh used oil and water to calculate the size of molecules

#100

Post by komali2 »

Cheer2171 wrote: post #91
komali2 wrote: post #81

Earlier quoted context omitted.

I'm confused, the blog wrote "known amount of water," so was it a closed little area like a bathtub? If you added a ton of oil wouldn't it spread out as much as possible aka 600 molecules thick or whatever? Or did he pour it into a huge lake or something?

One drop in a soup bowl sized petri dish, measure the area it covers.

Surely the first thing to test would be dropping it in increasingly large soup bowls until there's obvious gaps?
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