Archived posting to the Leica Users Group, 1999/02/18

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Subject: [Leica] Re: Diltilled water
From: Jim Brick <jimbrick@photoaccess.com>
Date: Thu, 18 Feb 1999 16:12:48 -0800

Thank you again, Alexey. I didn't think I was going nuts...

Jim

At 03:59 PM 2/18/99 +0000, you wrote:
>
>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
>            | PGP public key: http://pgp5.ai.mit.edu/ | voice:503/494-6840
>