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  1. #21
    Photo Engineer's Avatar
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    You have it correct Ian.

    The FORMATION of the bisulfite adduct releases base, but the alkali catalyses release by the paraformaldehyde with no overt pH change. Thank you.

    I have not done the Formaldehyde-Bisulfite reaction in the lab for nearly 50 years.

    PE

  2. #22

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    Quote Originally Posted by Ian Grant View Post
    This is quite obviously the explanation for how D85/AN79 works, it's quite possible if I'd added substantially more than 7.5ml of 40% Formaldehyde and waited sometime for the clock reaction to occur I wouldn't have needed to add a Part B

    So yes, the Paraformaldehyde dissolves, forms Formaldehyde, which in turn reacts with the Sulphite/(meta)bisulphite and liberates the hydroxide ion, which in turn forms Sodium or Potassium Hydroxide.
    I suspect you are right that simply adding sufficient formalin solution would have worked. It should have only needed 2.5 times of 7.5 mls to do it. (Paraformaldehyde is essentially 100% formaldehyde, so 100%/40% = 2.5 times needed.)

    I used to do formaldhyde analysis, and I could never get reliable results using formalin solutions as my source of formaldehyde. I switched to sodium formaldehyde bisulfite, and I was able to get check samples to be within 10% of the calculated value. The other nice thing about Na Formaldehyde bisulfite is that is dissolves easily in water.
    Kirk

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

  3. #23

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    Ok, from the Ted Pella. INC. web site http://www.tedpella.com comes this statement: "10% formalin and 4% formaldehyde on the one hand, and 4% paraformaldehyde on the other, are essentially all the same and differ only in the presence of a small amount of methanol in the former." So, apparently using 2.5 times the 7.5 ml of formalin would equal the 7.5 grams of paraformaldehyde.

  4. #24
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    Quote Originally Posted by bill williams View Post
    Ok, from the Ted Pella. INC. web site http://www.tedpella.com comes this statement: "10% formalin and 4% formaldehyde on the one hand, and 4% paraformaldehyde on the other, are essentially all the same and differ only in the presence of a small amount of methanol in the former." So, apparently using 2.5 times the 7.5 ml of formalin would equal the 7.5 grams of paraformaldehyde.
    Which is what Kirk has already said

  5. #25
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    Formalin and Formaldehyde are synonyms actually.

    Formaldehyde is a gas that dissolves in water. The water solution is called Formalin or colloquially 37% Formaldehyde. Chemically then Formalin is the water solution of a gas. The maxium concentration normally found, of Formaldehyde gas in water is 37% which is why the terms have become synonymous.

    So, 4% formaldehyde and 4% paraformaldehyde are the same but are not equal to 10% formalin since formlain is formaldehyde. Sorry.

    PE

  6. #26

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    So can anyone tell me what the difference between Kodalith and Kodalith Fine Line is. I have lots of the latter but I do not seem able to get it to produce any pink colour on lith prints the way my old Dupont Cronalith will.
    I suspect it is formulated to have less agressive infectious development.
    So what can I add to bring out some colour. A little Kbr maybe?
    Mark
    Mark Layne
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    and Barbados

  7. #27

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    Quote Originally Posted by Nicholas Lindan View Post
    Ansco 81 isn't bad. It doesn't have the rapid 'infectious' action
    of Kodalith AB, but it doesn't require any formeldehyde or lye,
    either. It keeps for months.

    Per liter:

    35. gm Hydroquinone
    55. gm S. Sulfite
    80. gm S. Carbonate
    5.5 gm Citric Acid
    10. gm P. Bromide

    Use full strength, developing time not longer than 3 minutes.
    Save for the citric acid and bromide the formula is similar to
    that of Wall's. Wall's cuts right to the lith phenomenon itself
    with no extras. Both Ansco 81 and Wall's use a carbonate
    to activate the hydroquinone.

    With low sulfite levels infectious development will occur as
    the byproducts of development produce even more energetic
    development and exponetionally more of the byproducts.

    A carbonate provides the high ph needed for reasonable
    development times. I've processed with a 50-50 blend of
    carbonate and bicarbonate with increased time. The
    generation of very high ph byproducts through the
    interaction of additional chemistries is beyond
    the needs of a lith developer.

    Formaldehyde is included as a slow release agent which
    maintains the necessary low sulfite level while at the
    same time increases the longevity of working
    strength lith chemistry. Dan

  8. #28

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    10% of saturated formalin (40% vol.) = 4% (vol.) formaldehyde

    Quote Originally Posted by Photo Engineer View Post
    4% formaldehyde [is] not equal to 10% formalin since formlain is formaldehyde.
    Ron,
    I think Ted is defining 10% formalin as a 1:9 dilution of 100% Formalin* with HOH;

    *
    100% Formalin being the saturated aqueous soluton of the gas
    which is 37% by weight formaldehyde... but 40% by volume.

    10% of 40% gives a 4% Formaldehyde gas solution.
    ----------------------------------------------------
    BTW, anyone see "Yes Man" ? It has a very tiny, yet nice, social commentary about Photography and Photographers... humor and a nice message as well!

    Ray

  9. #29

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    Quote Originally Posted by dancqu View Post
    Save for the citric acid and bromide the formula is similar to that of Wall's.

    Formaldehyde is included as a slow release agent which
    maintains the necessary low sulfite level while at the
    same time increases the longevity of working
    strength lith chemistry. Dan
    ------------------------------------
    I must have missed something!
    Walls What?

    In what is Formaldehyde included?
    Wall's, Ansco 81 or D-85
    ?

  10. #30
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    Quote Originally Posted by Ray Rogers View Post
    Ron,
    I think Ted is defining 10% formalin as a 1:9 dilution of 100% Formalin* with HOH;

    *
    100% Formalin being the saturated aqueous soluton of the gas
    which is 37% by weight formaldehyde... but 40% by volume.

    10% of 40% gives a 4% Formaldehyde gas solution.
    ----------------------------------------------------
    BTW, anyone see "Yes Man" ? It has a very tiny, yet nice, social commentary about Photography and Photographers... humor and a nice message as well!

    Ray
    Ray;

    That very well may be so but it should be specific as the context implies that formalin and formaldehyde are two different things when they are not.

    The statement, as posted above, is incorrect, regardless of intent by the poster or the originator.

    PE

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