Wayde Allen (wallen@boulder.nist.gov)
Thu, 14 Jan 1999 10:16:26 -0700 (MST)
On Wed, 13 Jan 1999 FotoDave@aol.com wrote:
> trying to figure out why my dichromate solution precipitated (and it
> precipitated badly. You can clearly see a layer of brown precipitates). As I
> said, I am suspecting the change of saturation point due to temperature, but
> it could be other reasons.
If your dichromate precipitated out due to a change in temperature
lowering the saturation point you should get orange crystals (precipitated
dichromate). Yet you say you are getting a brown precipitate. Is this
kind of a muddy film? I've seen this happen in my dichromate solutions,
and mine aren't mixed to saturation. It sounds like there was something
in the water that is reacting with the dichromate.
My sensitizing solution wasn't mixed with distilled water either, but I
figured that the sludge was caused by a reaction with dissolved organic
matter. After all, I immerse the carbon tissue in the solution to
sensitize it. I'm assuming that your solution is used as a stock for
mixing gum emulsions, and that it never comes into contact with organic
matter? I do have a potassium dichromate solution mixed to saturation, or
nearly so, that I've been using for mixing gum emulsions. It was mixed up
shortly after the first issue of the Post Factory Journal arrived, and I
don't think that there is any precipitate in this bottle - yet anyway.
I'll have to check.
- Wayde
(wallen@boulder.nist.gov)
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