Keeping an eye on puddle chemistry - front cover

a thermochromic plastic appearing as a circle with a dark blue rim, yellow and red inner ring with a very dark blue centre – looks like a mood ring.This cover photo is puddle chemistry at its best. A small amount of solid potassium chloride is added to a small puddle of water placed on a crystal temperature sensor. The cooling effect of the dissolving process alters the arrangement of molecules in the liquid crystal, creating a colour change.

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