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Thread: Question for the chemists

  1. #1

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    Question for the chemists

    Having first learned B&W processing with D-76 and Dektol back in days of yore, I remember clearly the instructions for mixing them at 125 and 105 degrees F, respectively. When I switched to D-23 several years ago, I followed the published instruction (Adams and others) to mix at 125. More recently, having used up my last Permawash, I have begun using sodium sulfite (with a seasoning of bisulfite) for wash aid and noticed that it mixes perfectly well, apparently, at processing temperature, 68-70.

    Having seen various recommendations to simply mix D-23 fresh at processing time (an attractive approach for consistency), but having always avoided this, due to the extra cooling time required (yes, I know about ice-cubes; not convenient to store in my situation), I began to wonder: If the sulfite dissolves at room temp, how about Metol?

    Just now I tried a little experiment. In 1 1/2 oz of 75-degree water, I dissolved a pinch of Metol, apparently successfully, in about a minute. I added a bunch of sodium sulfite and found that this, too, dissolved without much ado. Not to strict proportion, I understand, but in that direction.

    Therefore, my obvious question is, am I missing something here that is not visible but will affect the processing properties if I mix my D-23 at about 75, which will be much, much quicker for me to cool down? Is it not really mixing as well at this temp? Does the high temp affect the chemical properties in some way? Or, perhaps, is teh hig temp actually needed only for other components of developers such as D-76
    Philip Ulanowsky

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  2. #2
    Joe O'Hara's Avatar
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    Re: Question for the chemists

    If the solution is perfectly clear and there is no particulate matter on the bottom of the vessel, it is as mixed as it's ever going to get. The chemicals go into solution, individual molecules happily floating around in there.

    The advice to mix at higher temperatures is, I think, chiefly to make it easier to get 100 grams of sulfite to dissolve in a little less than a liter of water (of course you top it off to exactly a liter when you're done mixing).

    Let us know how this goes for you. It could save me some time too since I use D-23.

    If anything, the metol should oxidize less at lower temperature.

    I know only high school chemistry, but I think that's all that's needed here.
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  3. #3

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    Re: Question for the chemists

    Philip,

    To get the answer out of the way, if it dissolves completely in a reasonable amount of time at room temperature you can certainly do that. D-23 is a good example of a formula that easily mixes this way. You’re not missing anything.

    Heating the water before mixing (generally 38C, 40C thereabouts, up to 50C) is essentially a balance of mixing time (less time = less oxidation) and temperature (hotter = more oxidation).

    Sometimes heating is more helpful - for example if several ingredients are combined in one packet (in Kodak’s case along with sequestering agents to allow for single packages). Of course this is not a hard and fast rule. It depends on the ingredients and concentrations, but you get the idea.

    Michael

  4. #4

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    Re: Question for the chemists

    For D-76, you start with a pinch of sodium sulfite to keep the Metol from oxidizing, but that makes dissolving the Metol harder -- which is made easier with warmer water.

    I mix mine at room temperature, but I have a magnetic stirrer which dissolves everything -- well almost everything -- easily at room temp.

  5. #5

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    Re: Question for the chemists

    If you want, dissolve the Metol in 100 ml of hot water first, and add it to the remainder of room temp water. But be sure you add everything in order, starting with a pinch of sulfite (to scavenge oxygen from the water).

  6. #6

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    Re: Question for the chemists

    Thanks to you all; much obliged. I'll let you know what happens, beginning with a carefully measured fractional-amount test, including the de-oxidizing sulfite, which I forgot in my previous experiment, though I start with it normally. Stay tuned, though it's been around so long, I suspect others would have mentioned lower-temp mixing if it were practical. Why lead a boring life?
    Philip Ulanowsky

    Sine scientia ars nihil est. (Without science/knowledge, art is nothing.)
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  7. #7
    Tin Can's Avatar
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    Re: Question for the chemists

    Magnetic stirrers are cheap and very useful
    Tin Can

  8. #8

    Re: Question for the chemists

    Quote Originally Posted by Tin Can View Post
    Magnetic stirrers are cheap and very useful
    Agreed - magnetic stirrers help a great deal. Amazon has several that are both effective and inexpensive.

  9. #9
    Drew Wiley
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    Re: Question for the chemists

    I just use hot tap water, which is hot enough to dissolve the sodium sulfite. I no longer use either Dektol, D76, or D23, but did the same thing with them too. Haven't used a power stirrer in over 40 yrs. See no need for one personally. But it is amusing recollecting my younger days, wiggling my toes in equipment sales. I sold two of the first model of true cordless drill in this country to an orthopedic surgeon. Then a slightly later one I fitted with a stainless steel chuck for sake of stainless stirring paddles. Little did I know that much later on I'd be handling the same models used on the Space Station - and no, those are neither cheap nor sold on Amazon. But don't ask me how to mix Dektol in zero gravity.

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