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  1. #21
    gainer's Avatar
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    The purpose pf the patent system is to protect a person's interest in his own discoveries and designs without having to resort to secrecy. Now you read a patent disclosure and see that the range attempted to be controlled by the disclosure is so great that there has been no true disclosure. The patent I have read, about stabilized black-and-white developing compositions and methods of use, is a case in point. A manager, I reckon, gave these two experimenters a task to perform in as many different ways as they could think of. Was there a stroke of genius involved? Is that treatise expected to be put to use practically, or is it an effort at obstructionism?

    Sorry, I promised myself I would play with other threads.
    Gadget Gainer

  2. #22

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    Quote Originally Posted by jdef
    Despite not knowing how much sulfite is required to
    preserve 1-5g of metol in a liter of water, ...
    FX-1 uses your 1:10 ratio: .5 and 5. Beutlers uses a 1:5 ratio:
    1 and 5. But other factors influence the amount used; ph
    buffering and some thought for longevity are two.

    I put a Pan F+ 120 roll through 500ml of developer which
    had .3, .9, .9 gram metol, sulfite, carbonate. The solution
    was slightly yellow after 12 minutes and the negatives a bit
    contrasty. That, BTW, was a little Ansco 120/Beer's A.

    Your A bath is a five fold FX-1 or a short sulfite D23 used
    dilute. At that high ph the ascorbate, I think, a VERY
    active reducer. In situ regeneration of the metol
    takes place at a quick pace. Dan

  3. #23

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    Quote Originally Posted by Photo Engineer
    Please take note of the fact that ethylene glycol is very toxic. Propylene glycol is replacing it wherever possible in many applications.

    Ethylene glycol is particularly insidious due to its pleasant sweet taste. Be carful of it and solutions containing it around children and pets.

    PE
    Sorry about being so late with this opinion - ethylene glycol is not "very" toxic. It is probably best to say that ethylene glycol has low acute toxicity via oral, inhalation, or dermal exposure.

    From the first MSDS that came up online, the Oral Human Low Leathal Dose is listed as (ORL-HMN LDLO) 786 mg/kg. For a 80 kg person, that's about 62 grams of ethylene glycol.

    It is even added to some wines and a study found a maximum reported concentration (6.25 mg/litre) of ethylene glycol in wine in Italy (Gaetano & Matta, 1987).

    I do agree about the warning on accidental poisoning issues with children and pets. For photographic use, there should be no issues with it's use - at least as far as toxicity goes.

    IF you are interested in further study - this reference will be very helpful:
    http://www.inchem.org/documents/cica...ds/cicad45.htm

  4. #24

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    Quote Originally Posted by Ryuji
    Soon, I realized that photographic chemistry is a highly specialized branch of chemistry which an ordinary chemist specializing in areas outside photography would not understand very deeply.
    Boy, that's the truth. (I'm an ordinary chemist that has specialized in chemical analysis outside of photography.)

    Quote Originally Posted by Ryuji
    I know one decent book written for science-savvy photographers,
    Ryuji - Could you name this book?

  5. #25

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    Quote Originally Posted by Kirk Keyes
    Ryuji - Could you name this book?
    It's mentioned on my web site as well, but the one by E. N. Mitchell. The book doesn't spend many pages on chemistry but it is a comprehensive book on photography for general scientific audience.

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