|MadSci Network: Chemistry|
Most silica gel materials are color coded. This way, when they are saturated, they turn into a different color. You are right in saying that silica gel can be regenerated by heating to a high temperature to drive off the moisture absorbed. Their color is also restored.
They are kept away from other materials since they are hygroscopic and tend to absorb moisture, say from the palm of your hand etc. So its best not to handle them with your bare hands.
Regarding the test for silica gel, the formula for silica gel is actually Si(OH)4 which becomes Si(OH)4.H2O on hydration. The only chemical tests I can think off are mass spectrometry which essentially burns the material or ionizes it to release silicon which can be detected. A simpler, more mundane test would be to heat it to a high temperature (80-100C) and then see if it changes color. This will most probably be due to loss of moisture. I could not come up with a unique test for silica gel. Hope this helps.
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