MadSci Network: Chemistry

Re: Why do coal, ammonia, laundry bluing, and salt form crystals.

Date: Mon Nov 12 21:03:27 2001
Posted By: Artem Evdokimov, Postdoc
Area of science: Chemistry
ID: 1004011759.Ch

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.

Hope this helps.


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