|MadSci Network: Chemistry|
Hi John, |
Blueberries and grapes both contain a class of pigments called anthocyanins (sometimes mis-spelled as "anthrocyanins"). Anthocyanins can be used as acid/base indicators. They are red in acids , blue in neutral solutions and green-yellow in basic solutions.
What is the acidity level of your tap-water? I am willing to bet that as you add more water, the acidity slowly changes towards a neutral state. You can observe similar things when you eat red cabbage salad; watch what happens when you add salad dressing that contains vinegar.
One more point. Pigments do not scatter light. They work by selectively absorbing certain wavelengths of light and reflecting others. Rayleigh scattering doesn't occur in large molecules such as anthocyanins; you need rather larger particles.
Hope this helps.
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