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  1. #211

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    Quote Originally Posted by Photo Engineer View Post
    Alan; Back to the old argument. Well, tablespoons vary a bit in the US, and chemicals vary in crystal habit from batch to batch and even in one batch. I have found a variation of greater than 20% just due to crystal habit. This is often not accurate enough. It depends on the effect of the chemical in question. PE
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    Electronic gram scales are available for only $10 to $15!
    Search for "gram scale .01" on amazon.com. Here they are:
    http://www.amazon.com/s/ref=nb_sb_no...gram+scale+.01

    Cost cannot be an objection at such a low price, and it solves all measurement issues. Weighing powders is more accurate. I prefer to weigh liquids as well, as it's more accurate and convenient.

    Mark Overton

  2. #212
    kb3lms's Avatar
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    You've gotta watch those electronic scales from Amazon. I bought one a year or so ago and later found that it is exactly 1.5 grams off across the board. Haven't found a way to zero it although you would think there would have to be one. The electronic scales can work but you have to make sure you get a good one. Some are and some are not. I got a brand called AWS. Probably not the best. Thankfully I did not pay much for the scale although I messed up a few concoctions with it.

    For a few dollars more, careful shopping on the auction site will get you a used Ohaus triple beam balance. There are other brands that likely work just as well for our purposes. I paid right around $30 for mine. Little cleaning and it is just like new and right on the money every time.

    If you want to mix developers and such you really want a respectable scale. Top of the line is not necessarily needed though.
    All this has happened before, and all this will happen again.

  3. #213
    Photo Engineer's Avatar
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    You can buy sets of weights in English or Metric values. These can be used to either calibrate or verify the calibration of your scales.

    I have two digital scales and several sets of calibration weights. With mine, I just put a weight on the scale and then press the calibrate button.

    You press the button and it does the rest. Hmmm, that sounds familiar!

    PE

  4. #214

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    Quote Originally Posted by kb3lms View Post
    You've gotta watch those electronic scales from Amazon. I bought one a year or so ago and later found that it is exactly 1.5 grams off across the board.
    If it won't calibrate as PE suggests, then that scale is defective; is it too late to return it under warranty? I have two scales from AWS (American Weigh) bought via amazon, and both work fine and agree with each other. But I'll admit that the more expensive milligram scale (.001 resolution) glitched once, creating a mystery brew that worked great but I can't reproduce.

    Mark

  5. #215
    Cor
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    Hi Mark,

    thanks for the elaborations! Strange that your syrup coloured brown so quickly, in my experience it is a very slow process. After all it's mixed in glycol to retard oxidation, and I believe that Phenidone is still working properly despite the colour shift.

    But as you say it might very well be the quality of the TAE, mine is of high purity from Fluka I believe. In my non -scientific test it behaves the same as Xtol 1:1.
    Although I now mainly use it now on a a new to me film: Fomapan 100, needs some fine tuning though, contrast is too high, but this film is said to build up contrast easily anyway.

    I'll will you follow your results with great interest, keep up the good work and thanks!

    Best,

    Cor

  6. #216

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    Quote Originally Posted by Photo Engineer View Post
    Kork said noting about NaOH being difficult to dissolve. He was describing a lab technique that allowed one to prevent formation of big chunks of NaOH. Instead, by swirling, he formed a thin film of NaOH.
    That's exactly it - I needed to get the NaOH into a form that I could quickly and easily dissolve it and then transfer it into a 100 mls volumetric flask. We would digest about 20 plant samples at a time so getting into solution in a timely manner was of great importance.
    Kirk

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

  7. #217

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    Quote Originally Posted by albada View Post
    Yes, that thing is going to spoil me. But I figured out a trick for getting a temperature into the meter: apply a resistance to the ATC connector using a potentiometer. That way one can simply dial-in the temp seen on the thermometer. This evening, I tried various resistors and got a table of corresponding temperatures from the meter, so now I know what kind of resistor-network to solder together. That's another electronic hack until I find a temp probe (and I like your idea of an electrode with built-in temp sensor).
    Since you like playing with electronics, you should just make yourself a temp probe. You've discovered the "secret" of the ATC probe that it's simply a resistance sensor - look around for a 10K thermistor as I think that's what's used in ATC probes. You may need an additional adjustable resistor to adjust the base reading of the termistor. Check you're owner's manual as it may say.

    Then search around here on APUG in the emulsion making forum - I think PE and I posted photos of ion specific electrodes that we had made. You can use the same technique to make the ATC probe. Get a length of glass tubing that's long enough to support with your pH electrode and reach the solution, and also big enough in diameter that you can slip the thermistor and wires into the end of it. Thinner glass will give quicker response time but you want it thick enough that it will be rugged enough.

    Then use a torch to seal one end of the tube and fire polish the other end. After it's cooled, use a smaller tube to transfer some epoxy into the seal end of the glass tube. Then QUICKLY insert the thermistor and lead wires into the electode housing and set them into the epoxy. Then seal the open end of the glass tubing with some more epoxy.

    Fit whatever connectors you need for your meter, and you're all set!
    Kirk

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

  8. #218

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    Quote Originally Posted by albada View Post
    <...> As pH rises, Phenidone's B+F rises.
    I need to modify the above statement that I made a few weeks ago. In that posting, I made two claims: (1) that Phenidone produces higher fog than DimezoneS, and (2) that Phenidone's fog rises as pH rises. The second claim I made is false. pH does not affect Phenidone's fog-level. Further testing shows no relationship between fog and pH. The graph I posted showing a correlation must have been due to happenstance. I still see Phenidone producing a bit more fog than DimezoneS, about .02 higher typically, a small enough difference that most people will neither notice nor care.

    Mark Overton

  9. #219

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    Quote Originally Posted by Kirk Keyes View Post
    Since you like playing with electronics, you should just make yourself a temp probe. You've discovered the "secret" of the ATC probe that it's simply a resistance sensor - look around for a 10K thermistor as I think that's what's used in ATC probes. You may need an additional adjustable resistor to adjust the base reading of the termistor. <...deleted details...>
    I had not thought of that! Perhaps because I'm not familiar with thermistors. It appears that Beckman meters want a 30K thermistor, probably like this one:
    http://www.digikey.com/product-detai...2132-ND/739878

    Beckman sells new temperature probes for US$109, but it's tempting to DIY as you described. Thanks for posting the info.

    Mark

  10. #220
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    Mark, have a look at the LM35 devices from Texas and National. The output is detected on a millivolt scale on your meter and gives a direct readout in Centigrade.
    Maybe it has sufficient accuracy for your needs. I cobbled one together using the wires as the detector since the input of the TO92 device is the wires themselves. You may even want to use a small piece of PCB to increase the speed of settling.

    Murray



 

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