How is the measurement for the area the oil has spread over performed? Visually or some other way?
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
#12These 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.
Re: In 1870, Lord Rayleigh used oil and water to calculate the size of molecules
#13> 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.
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.
Re: In 1870, Lord Rayleigh used oil and water to calculate the size of molecules
#14I 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)
Re: In 1870, Lord Rayleigh used oil and water to calculate the size of molecules
#15That 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.
Re: In 1870, Lord Rayleigh used oil and water to calculate the size of molecules
#16> 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.
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Seems questionable that Rayleigh would have known that oil molecules are hydrophobic on one end and hydrophilic on the other.
Re: In 1870, Lord Rayleigh used oil and water to calculate the size of molecules
#17How is the measurement for the area the oil has spread over performed? Visually or some other way?
The 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_lite...
Re: In 1870, Lord Rayleigh used oil and water to calculate the size of molecules
#18Re: In 1870, Lord Rayleigh used oil and water to calculate the size of molecules
#19> 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.
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> Cortesy of ChatGPT:
Can we not, please? At the very least not unless you personally have the knowledge to confirm that ChatGPT didn't make any mistakes, as it did here.
Re: In 1870, Lord Rayleigh used oil and water to calculate the size of molecules
#20How is the measurement for the area the oil has spread over performed? Visually or some other way?
Some 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.