|MadSci Network: Chemistry|
Dear Mary, Here's what happens in your 'crystal garden' experiment: Coal has a developed surface, and lots of microscopic channels traversing it from the inside. In essense, coal is like a sponge. When you pour the salt solution (with blue for color) on the coal, it eventually gets absorbed, and begins to evaporate from the top, where contact with air is highest. Crystal clusters form whereever the concentration of salt reaches supersaturation threshold (with coal serving as crystallization nucleation sites) - these crystals trap some of the blue dye so they become irregularly colored. More solution diffuses through the coal, 'feeding' the growing crystals. http://atoms.org.uk/ http://www.sciencenet.org.uk/publications/crystal.html http://freeweb.pdq.net/headstrong/CHARCRYS.HTM Hope this helps. A.G.E.
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