MadSci Network: Earth Sciences

Re: Why are salt crystals forming on the outside of a glass instead on a string

Date: Sun Apr 1 22:31:57 2001
Posted By: Alex Barron, Graduate Student, Ecology(Biogeochemistry)
Area of science: Earth Sciences
ID: 985238491.Es

    It is hard to say for sure what is going on without looking at your 
particular setup.  The way this experiment is supposed to work is that the 
solution gets pulled up out of the glass in the small spaces in between the 
fibers of the string (this is called capillary action).  Then, gravity 
makes the liquid flow to the middle of the X, which should be slightly 
lower than the rim of the glass.   Solution accumulates there to the point 
where it begins to drip to form the stalactites and stalagmites (which in 
real life are formed by calcium carbonate not Epson salts).  I suspect that 
the rim of the glass may pinch the capillaries in the yarn shut.  This 
could cause the liquid to leak out in a very thin layer that would spread 
around the rim of the glass and evaporate, leaving the salt behind and 
never making it to the "X".  You might want to try different types of 
string to see if that solves your problem.


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