A perfect storm in a cup of salt water?

[CharlesConcord]

Hi all:

I have been puzzled by a very simple experiment I did lately. I found there exists a temperature gradient in a cup of saturated salt water--the bottom is about 0.5 Celsius warmer than the top. That is after the solution has been left intact for more than 100 hours. There is no such temperature gradient in a cup of pure water or unsaturated salt water.

I documented these experiments in my blog:

http://molecularworkbench.blogspot.com/2010/09/why-is-bottom-of-cup-of-salty-water.html
http://molecularworkbench.blogspot.com/2010/09/evaporation-is-driving-force.html
http://molecularworkbench.blogspot.com/2010/09/temperature-gradient-only-exists-in.html

I am going to continue my experiments to figure out why. In the meantime, can anyone enlighten me?

Charles Xie

 

[CharlesConcord]

Well, I figured it out myself last night.

http://molecularworkbench.blogspot.com/2010/09/mystery-solved.html

 

[Mapes]

Nice!