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When you mix a solid into a solvent you can see weird patterns right after the mixing. A common example is mixing sugar in water.

What are those wave-like patterns and why do they happen?

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  • $\begingroup$ This I think might be a better question for physics.SE, providing that they want it. $\endgroup$ – M.A.R. ಠ_ಠ Mar 19 '16 at 10:34
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    $\begingroup$ "Schlieren" or "schlieren lines." Definitely physics. $\endgroup$ – SendersReagent Mar 19 '16 at 10:43
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Those rippling transparent patterns are caused by the variations in refractive index, which in turn are caused by the variations in concentration of the solute. As soon as the dissolution and mixing is over, and the solution is uniform again, the patterns are gone. I don't know the English word for it, or whether there is one; "Schlieren" seems to be much more general.

It's a physical phenomenon indeed, but chemists might be more used to seeing it.

You may observe a remotely similar pattern around a heated object in the air (see "heat haze"). In that case, it is caused by the variations of temperature and not concentration.

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    $\begingroup$ I think English uses the same German(?) term, 'Schlieren'. It's the only term I can recall having been used for it. $\endgroup$ – hBy2Py Mar 19 '16 at 12:50
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    $\begingroup$ Schlieren is very general, but it happens for the same reason as any other schlieren. $\endgroup$ – SendersReagent Mar 19 '16 at 18:23

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