Archived posting to the Leica Users Group, 1999/02/18
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Date: Thu, 18 Feb 1999 14:19:39 -0400
From: "Robert G. Stevens" <robsteve@istar.ca> wrote:
> I will have to side with Ken on this one. I remember in High
> School Biology class we did an experiment on Osmosis in cells.
> With distilled water the cells would blow up and some explode.
> I think it had to do with the difference between inside the cell
> and outside.
Osmosis is driven by different solute concentrations in
compartments divided by a SELECTIVELY PERMEABLE membrane.
This has zilch to do with photographic chemistry.
>I don't know wheter it is trying to equalize the salinity or what,
Close enough (to describe osmosis, not film emulsion swelling).
> I think the emulsion is gelatin
Yes.
> and made of cells.
No. Gelatin is a mixture of (mainly) extracellular glycoproteins such as
albumin. These shrink when dry, expand when hydrated. Long exposure to
water, especially hot water, causes swelling. The difference in salinity
between tap water and distilled or deionized water is small enough that
there should be ZERO difference in emulsion swelling.
Those residual salts *can* cause spotting, however, and for this reason
I do my final wash in distilled water (with Photoflo or NP40 detergent).
..........................................................................
Alexey Merz | URL: http://www.webcom.com/alexey | email: alexey@webcom.com
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