I'm trying to study the Tea leaf paradox, and asked a question about it on physics.stackexchange.com. To get further on the problem, I want to make a solution of very small objects in water that are distinguishable to the naked eye, and have (very close to) neutral buoyancy. I teach at a high school and have access to the chemistry lab here. Suggestions?

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    $\begingroup$ This is not called a solution. Solution means that whatever is in the water has been "dissolved", that is, broken and dispersed into individual molecules. What you are describing is a suspension - meaning the particles are much bigger than individual molecules. $\endgroup$ Nov 27 '19 at 22:46

I think that the cheapest and fastest way is that of working on natural products, like actual tea leaves, or ground coffee (I just tried it with coffee, and it can be done):

If you want only particles with neutral buoyancy, or, if I understand well, floating in the solvent, you can use said natural products, which contain particles of different shapes and densities, and discard by fractionation the unwanted ones.

What I did:

  • Place the ground coffee in a glass of water and stir a lot.
  • Let the suspension sit. You will notice that part of the parcticles are on a top layer, some are floating in water, and some are at the bottom.
  • Put the glass in a sink, and gently add water to it, so that the top layer eventually falls out of the glass, together with some water
  • Let the suspension sit: if needed repeat the last step, otherwise go on
  • To discard the bottom layer, gently pour the solution in another glass, by leaving some water in the first glass: the first glass will contain the heavier bottom layer, and the second one will contain only floating parcticles
  • If needed, repeat the last step
  • $\begingroup$ Brilliant! I will try that. $\endgroup$ Nov 27 '19 at 21:18

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