Re: Ammonium Dichromate

From: T. E. Andersen ^lt;[email protected]>
Date: 12/29/04-08:17:34 PM Z
Message-id: <41D3653E.2040008@microscopica.com>

Loris Medici wrote:
> (...) Actually, you "should" have some undissolved solid in order to
> guarantee a saturated solution. If I'm right, 60gr AD in 150ml water
> should make a 28.5% solution. As water solubility of AD is around 25%
> (IIRC, @ room temperature), your solution is a saturated one - you can
> use it comfortably, just make sure that you don't have solid in your
> coating mixture.

I notice, with some surprise, that many people working in alt.photo use
saturated solutions (for this and other purposes). I have even seen
writers (not only on the web, but also in published books) stating that
a saturated solution is a constant and repeatable mixture.

Please note that this is ONLY true if you have constant temperature.

I think it is generally much better to choose a concentration just
bellow saturation at your minimum working temperature. That way, you
will always have the same concentration of the compound in question. So,
if your lab temp is in the range 15 to 25 oC, choose a solution that is
saturated at 14 degrees. Then, you will have the same mixture all year
round.

If you use a saturated dichromate solution, you will be working with
different concentrations depending on whether you have 15, 20 or 25
degrees (centigrades) in your lab. Doesn't really ADD to predictability...

Best regards,

Tom Einar Andersen
Received on Wed Dec 29 20:24:25 2004

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