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How is the measurement for the area the oil has spread over performed? Visually or some other way?
I 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?"
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.
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Seems questionable that Rayleigh would have known that oil molecules are hydrophobic on one end and hydrophilic on the other.
No idea. I was curious myself and decided to ask our "guru". The answer seems a bit fishy
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Seems questionable that Rayleigh would have known that oil molecules are hydrophobic on one end and hydrophilic on the other.
If it was, I'm sure he knew that soap oils are both hydrophobic and hydrophilic and had ways of figuring out that soap oils consist of a single type of molecule and aren't a mixture.
> 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.
He didn't. It was an assumption
How 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.
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…
> 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.
Rayleigh's experiment was actually trying to solve for the minimum thickness of oil required to stop some camphor shavings from moving around on the water. He never states it explicitly, but I think the assumption is that the minimum thickness required to stop the shavings' movement would be such that the oil volume 'just' covers the surface, ie. is 1 molecule thick everywhere and hence the shavings never touch water. I think he's specifically making a slightly more clever point about surface tension, but that's a little beyond me.
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)