Re: precipitation of dichromates

Chris,
Potassium dichromate is insoluble in alcohol, ammonium dichromate is
soluble, although I do not have the exact solubility numbers. You gum
solution is mostly water anyway. If you like to print with concentrated
dicromate solutions (around 15% in the final solution or even higher)then
it is likely that you can not add a lot of alcohol, or else potassium
dichromate will precipiate. Again the alcohol addition is also small,
maybe 5%. If you are printing with a dilute dichromte solution you might
not have a problem with potasssium dichromate and alcohol. This is one of
those things that it is so much easier to test in practice anyway.
Happy printing
Marek Matusz, Houston

> Do any of you chemists out there know why potassium dichromate would
> precipitate out of solution when alcohol is added vs. ammonium dichromate
> which doesn't? Could it just be potassium's lower saturation point that
> makes it seem that way or is there a property of alcohol that makes a
> potassium form do this whereas an ammonium form doesn't? Or is this even
> true in your observations, and from a practical standpoint, at what point?
> Any conjecture would be appreciated.
>
> My reason for asking this is just thinking about the addition of alcohol
> in
> a coating solution in gum printing that has been suggested in the past, to
> make it thinner and easier to coat, whether this is viable with potassium
> dichromate.
> Chris
>
>
>
Received on Tue Feb 24 12:36:55 2004