I 'm making something and I have a question someone here might know the answer to: What would ma...

[G+_George Kozi]

I'm making something and I have a question someone here might know the answer to: What would make a better thermal masss, very fine sand, or salt?

 

Both will be contained in a glazed clay pot. The heat source is 5 to 7 tealight candles that would burn for 6 hours around and very close to the thermal mass. There also is a conical ceramic "roof" over the whole thing to trap the heat. 

[G+_610GARAGE]

My gut says to go with sand, but I have no evidence of it. :) I do know that when you weld cast iron, people say to bury the piece in sand to reduce the cooling rate of the metal. And metal casts are made out of sand, possibly for the same reason. Also, sand will compact better, therefore giving you more mass to heat, and making the heat transfer more efficient. Another thing to consider; if the salt gets wet, it will not only dissolve, but rust out any metal near by, over a period of time of course.

[G+_Jim Vandiver]

I think what you are looking for is specific heat and here's a link that shows sand and salt: http://www.engineeringtoolbox.com/specific-heat-solids-d_154.html . You'll have to research what specific heat means for a better feel. They're close, but salt looks better which is probably why is has been used in the past for storing heat in solar setups.