Here, I've found the answer :

What is silica gel and how does it work?
Silica gel is a desiccant, or drying agent, that was patented in 1919 by Walter A. Patrick at John Hopkins University in Baltimore Maryland. Despite its name, it is not a gel and should not be confused with silicon gel. Silica gel is a porous, granular form of silica, (...)


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• 40 gram silica gel canister protects up to 3 cubic feet.
• 200 gram silica gel unit protects up to 15 cubic feet.
• YOU GET THE IDEA ...

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source : http://www.theruststore.com/Silica-Gel-FAQ-W40C2.aspx



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