What is the size of a single molecule of oil? What may initially seem like a trick question – answerable only through the use of complicated, high-tech scientific equipment – is actually as easy to calculate as the circumference of planet Earth. Much like how [Eratosthenes] used a couple of sticks to achieve the latter feat back in about 240 BCE, the size of a molecule of olive oil was calculated in 1890 by [Lord Rayleigh], which is the formal title of [John William Strutt]. Using nothing but water and said olive oil, he managed to calculate the size of a single olive oil molecule as being 1.63 nanometers in length.
To achieve this feat, he took 0.81 mg of olive oil and put it on a known area of water. Following the assumption that the distributed oil across the water surface would form a monolayer, i.e. a layer of oil one molecule thick, he divided the volume of the oil by the covered area, which gave him the thickness of the oil layer. Consequently, this result would also be the dimension (diameter) of a single olive oil molecule.
Many years later we know now that olive oil is composed of triacylglycerols, with a diameter of 1.67 nm, or only about 2% off from the 1890 estimate. All of which reinforces once more just how much science one can do with only the most basic of tools, simply through logical deduction.
I thought that I discovered that when I took high school physics.
That does look like a page right out of my ancient PSSC physics textbook…
Though the link implies it’s even older than that.
I can’t find the text right now, but the PSSC Physics lab went something like this:
Prepare a large pan of water, allow to settle.
Sprinkle chalk dust lightly on the water surface.
Dilute a small quantity of oil accurately in a large quantity of alcohol, 100:1 or so.
Measure the volume of a single eyedropper drop of the solution (drip 100 drops into a graduated cylinder), and calculate how much oil is in a single drop.
Drop one drop of alcohol-oil on the water and wait for it to settle: the floating oil solution spreads away the chalk dust, and the alcohol evaporates, leaving a one-molecule thick disk of oil, demarcated by the dust edge.
Measure the diameter, and from the known volume of oil present, calculate the thickness of the disk.
Assume it’s a monolayer, and boom: there’s your molecule size (or at least one dimension of it)
I contest the very idea that “a molecule of olive oil” exists.
OK. Prove it doesn’t.
In fairness, olive oil contains multiple different fatty acid triglycerides, as well as other molecules, so you can’t really say that a single molecule is, itself, olive oil. I suppose you can argue that this calculates an average size, but then that ignores sterols and other things which are in there too.
Still a fun exercise though.
Fair enough. There is no singular “olive oil”, so it would be fair to say one molecule of it can’t exist.
I leave proving non-existence of widgets for the experts.
Fair doesn’t enter into it. It is correct to say that no molecule of olive oil exists because there is no such thing. Sheldon out.
The cunning better-than-thou Possessor of Truth is correct and will go drink his gloat milk now.
I thought Benjamin Franklind did the experiment before ??
it seems like a big step from experimentally determining a minimum thickness of oil to asserting you know the shape or orientation or layering of the molecules that compose it.
you can do a lot easily with simple methods but the hard parts are still hard even if you can come up with a simple experiment in the end.
A lot of whinging when this is good applied mathmatics and if it was necessary to determine the thickness of a molecule you’d have it to a good enough approximation for whatever practical purpose you’d put the number to.
I fondly remember this experiment from 1970 science class. Lord Rayleigh got a better value but there is nothing like hands-on experiments.
Same class, same instructor, had a tape recoding from one of the Apollo landings in which there was an “echo” in the voice recordings. By measuring the lag and starting with an estimate of the earth-moon distance, we calculated the speed of light.
Fun times.