bfesser
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Hygrometers in Desiccators
Does anyone here keep a hygrometer in their desiccator?
I just purchased a pair of cheap (~6 USD) dial hygrometers from a pet shop to monitor my desiccator. I think the hygrometers are intended for
terrariums. I placed one hygrometer inside my Drierite (anhydrous calcium sulfate) desiccator a few days ago, and the other has been sitting on my
desk for comparison.
I just took a look at my desiccator, and it appears that the needle of the hygrometer has dropped well below 0% humidity on the scale. The one on the
desk still reads around 40% (I made sure that I bought a pair which showed the same humidity reading while on the shelf at the store). What does this
mean? Is the CaSO4 giving off corrosive gasses which have attacked the fine metal coil in the hygrometer?
[edit]
I suppose it would be easy to remove the hygrometer into the outside atmosphere and see if the reading returns to match the control hygrometer. I
hesitate to do this, however, because I store my most expensive hygroscopic and light sensitive reagents in this desiccator. I prefer to avoid
introducing moisture or gasses which could degrade the reagents and will hydrate the desiccant. The less I open it, the better. (I'm also paranoid
about chipping the now flawless ground seal.)
[Edited on 6/2/09 by bfesser]
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not_important
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No, it means that they are indeed "cheap dial hygrometers", intended for monitoring normal humidity ranges as found in nature and which rarely drop
below 20% for most dry regions where animal life is found.
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Adding anhydrous copper sulfate can tell you whether your salts are wet (although this is far as precise).Theoretically your desiccator shouldn't
contain any water at all.
The seal can be treated with vacuum grease and that will ensure it to be leak-free.
What a fine day for chemistry this is.
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