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  1. #21
    Photo Engineer's Avatar
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    Ray;

    At 0.1 g/l, the value given above, I assure you that the vAg is positive. In a plot, this does not show up well though and for the most part work is carried out in the negative range for NaBr. For NaCl though, most all values are positive, and for KI they are not positive at all IIRC.

    PE

  2. #22

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    Quote Originally Posted by Photo Engineer View Post
    Ray;

    At 0.1 g/l, the value given above, I assure you that the vAg is positive. In a plot, this does not show up well though....

    PE
    Thanks for the clarification....

  3. #23

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    I think by converting the Molar concs of the x-axis into log(mole conc) will give a pretty straight plot for the curves and you can also see that the lines go into positive values as the concs get lower than 1 Molar.
    Kirk

    For up from the ashes, up from the ashes, grow the roses of success!

  4. #24
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    Quote Originally Posted by Kirk Keyes View Post
    I think by converting the Molar concs of the x-axis into log(mole conc) will give a pretty straight plot for the curves and you can also see that the lines go into positive values as the concs get lower than 1 Molar.
    Oh, I agree, but then someone would say "why are you using logs, why not 'real numbers'?"

    You cannot please everyone at the same time but you can anger or annoy everyone at the same time.

    PE

  5. #25

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    I think PT Barnum said that once.
    ;^)
    Kirk

    For up from the ashes, up from the ashes, grow the roses of success!

  6. #26
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    Quote Originally Posted by Kirk Keyes View Post
    I think PT Barnum said that once.
    ;^)
    He said "You can please some of the people some of the time but not all of the people all of the time!"

    Or maybe it was someone else. IDK. I am unsure because I don't want to displease anyone.

    PE

  7. #27

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    Kirk, to do that would involve extrapolation, correct?

    Which method of extrapolation would you consider suitable for this data?

    Similar data I have seen before has always been on logarithmic graph paper... and covered the full range of interest; if you find your Excell sheet perhaps it can be fleshed out a bit without the need for extrapolation....

    A similar version:
    You may fool all the people some of the time,
    you can even fool some of the people all of the
    time, but you cannot fool all of the people all the time.
    Last edited by Ray Rogers; 06-24-2010 at 08:24 PM. Click to view previous post history.

  8. #28
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    Ray;

    This mV chart is limited by the pAg scale and by the PKSPs of the halides. Therefore it asymptotically approaches a limit at each end. The low limit is AgI at about -300 or more mv and the upper limit is AgCl at about +250 mv. Mixes are in between. A log scale would be linear in shape but not in concentration as is obvious and may confuse some people. A non-log scale is not linear as shown in my example above.

    Extrapolation is not necessary as the curve I showed is entirely calculated and is therefore an extrapolation itself requiring only more data and "running time" to extend the curve. But, this serves no purpose in most cases as we only need to know that about 0.1 g/l of NaBr or a vAg of about -50 to -70 mv at 40 deg C is optimum for keeping and fog prevention. This comes from the basic properties of Silver Halides.

    The same can be said for the final pH of an emulsion BTW. However, in this case it controls speed and contrast instead of fog and keeping.

    PE

  9. #29

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    Quote Originally Posted by Photo Engineer View Post
    ... about 0.1 g/l of NaBr or a vAg of about
    -50 to -70 mv at 40 deg C
    cf

    Quote Originally Posted by Photo Engineer View Post
    ... At 0.1 g/l, the value given above, I assure you that the vAg is positive.

    ???

    It looks like the VAg in both quotes (both 0.1 g/l) have different signs...
    Last edited by Ray Rogers; 06-24-2010 at 10:38 PM. Click to view previous post history.

  10. #30
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    Update:

    I managed to build a prototype of a 35mm perforator. It wasn't impossible at all, in fact I'm surprised I made it in one night (that was an all-nighter, though). Perforations look quite awful, but IT WORKS, and I believe it's usable because the requirements are not so high in still photography. Perforating two holes at a time is tedious so I started to automate it. I made six large electromagnets that hopefully will be strong enough to punch the holes. I'll post more details later!

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