Drierite a brand name of a commonly-used, calcium sulfate-based dessicant in many chemistry labs. The lab I work in has a dessicator box we use to store hygroscopic materials. It isn't a a true dry box, just an air-sealed box with a big tray of dessicant at the bottom. A cheap humidity meter we bought suggests the humidity gets down to 25% or so in there. We store minute quantities of amine solutions in the box, and some hygroscopic dry materials.
Most drierite pellets are something like pure calcium sulfate, and are therefore a colorless white. But some pellets are laced with cobalt chloride, a water-sensitive "indicator" of drierite freshness. Supposedly, as the drierite absorbs moisture, the cobalt chloride turns from a sky blue into a pinkish color. When it turns pink you know it's time to change the dessicant to a fresh dry batch.
But our drierite never turns pink.
Instead it turns into a far, far more intense, vivid blue color, much bluer and less pale than indicator drierite starts out as. (See photo of too-blue drierite in tray, with a bottle of fresh starting indicator drierite at left.)
Why doesn't my drierite turn pink?. Why does it turn this shade of blue? Presumably some other kind of complex or hydrate rather than the classic cobalt chloride hexahydrate is forming. Is it an issue of pH? Or of some volatile organic being adsorbed?
