Archived posting to the Leica Users Group, 1999/02/18
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]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 >