Demonstration of the Gibbs-Marangoni effect

A thin layer of water (with some red dye to improve its visibility) is laid upon a flat surface. Then drops of alcohol (denatured ethanol) are added. Where the alcohol meets the water, the liquid rushes out, sometimes drying a spot on the surface completely.
This is a consequence of the fact that the surface tension of water is significantly greater than the surface tension of alcohol, and the surrounding water therefore pulls more strongly on the alcohol than the alcohol can pull back on the water. This is an instance of the "Gibbs-Marangoni effect": the flow of a liquid caused by a gradient of surface tension. In the context of the "tears of wine" phenomenon, this effect was actually first explained in 1855 by James Thomson, the older brother of Lord Kelvin.
This simple demonstration is described in the classic work of scientific popularization Soap Bubbles: Their Colours and the Forces Which Mould Them (Dover Books, 1959 [1911]) p. 32, by the English experimental physicist Sir Charles Vernon Boys (1855-1944).
See:
Marangoni effect (Wikipedia): en.wikipedia.org/wiki/Marango...
Tears of wine (Wikipedia): en.wikipedia.org/wiki/Tears_o...
C. V. Boys, _Soap Bubbles_: archive.org/details/cu3192403...

[@estebancontreras1537]

How it works?

[@Gibbsian36]

The surface tension is greater for water than for alcohol. I give details and references in the description for this video.