Refinery
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Preparing CaSO4 drying agent from gypsum
I recently made some CaSO4 drying agent from ordinary bulk gypsum. All I did was spread it on oven pan and heated it up to 250C for few hours. It
turned from optical white to dull white. Should it be ready to use as drying agent after this treatment?
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Sulaiman
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cut & paste from Wikipedia;
"On heating to 180 °C (356 °F), the nearly water-free form, called γ-anhydrite (CaSO4·nH2O where n = 0 to 0.05) is produced. γ-Anhydrite reacts
slowly with water to return to the dihydrate state, a property exploited in some commercial desiccants. On heating above 250 °C, the completely
anhydrous form called β-anhydrite or "natural" anhydrite is formed. Natural anhydrite does not react with water, even over geological timescales,
unless very finely ground."
CAUTION : Hobby Chemist, not Professional or even Amateur
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Refinery
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What very finely means in this context? The powder I got is pretty much as fine as it can get.
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Belowzero
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The weight loss can be easily calculated and measured.
Many hydrates can be dehydrated using a microwave , care should be taken not to melt the container 
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Ubya
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well test it then! gypsum is already a slow acting dessiccant, you might want to get it as fast active as possible
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Refinery
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Only reason I don't use magnesium sulfate is that it is according to sources slightly acidic and the reagent I'm drying can degrade by hydrolysis into
unwanted products in presence of water if it's acidic.
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