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  1. #1

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    Water content of Arm & Hammer washing soda?

    Does anyone know what form Arm & Hammer's Washing Soda is (anhydrous, monohydrate, decahydrate, or something else)? I want to use it as a source of sodium carbonate, but I don't know its water content so I don't know how much to use. I can convert from one form to another, but I don't know what I'm starting with.
    Bob Walberg

    The fix is in!

  2. #2

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    I don't know, but usually when I use it to make Caffenol, I'm mixing with water anyway.

  3. #3

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    I believe that it is the monohydrate as this is the only form that is stable at ambient temperature and humidity. However it is only technical grade and does contain some iron as an impurity. I would not recommend its use for ascorbate developers. It is good enough for paper developers. There are two suppliers of photograde chemicals in the US that I am familiar with; www.techcheminc.com and www.chemistrystore.com. I don't know if they will ship to Canada. As a last resort you can prepare anydrous sodium carbonate from USP grade Arm & Hammera Baking Soda. Place the baking soda in a glass or stainless steel baking pan and heat it at 350 F for an hour. Heating it for longer will not hurt it but it should be a minimum of an hour. Stir it a couple of times while heating. The baking soda will change from fine crystals to a fluffy powder. Allow it to cool and store in a tightly sealed container as it will absorb moisture and convert to the monohydrate.

    The reaction is 2NaHCO3 ---> Na2CO3 + CO2 + H2O
    Last edited by Gerald C Koch; 06-24-2012 at 11:58 PM. Click to view previous post history.
    A rock pile ceases to be a rock pile the moment a single man contemplates it, bearing within him the image of a cathedral.

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  4. #4

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    We've had a couple discussions about that over on Flickr; for example, here. My measurements (outside of one outlyer) showed about 9% water by weight. I don't have a good sense of how stable it is however. For completeness, I should also mention that I live in a very dry climate.

  5. #5

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    Where did u find it? All i could find at stores was A&H laundry soap now.

  6. #6

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    In the UK ,widely available Dri-Pak Soda Crystals are labelled as containing greater than 30% sodium carbonate decahydrate.I phoned them up and spoke to a technical guy from the factory who told me the crystals in fact contain 99% decahydrate.There is now some anomaly in the packing regulations that causes >30% to be written on the packs (sounds like the EU again).I have not actually done the heating test to confirm this.

  7. #7

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    Rheinhold's Caffenol blog gives some information which may be useful http://caffenol.blogspot.co.uk/2010/...-truth_07.html

  8. #8

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    Where are you ezwriter? Grocery stores would be my main target to check, at least here in the US. But it is really hit or miss, so you may have to look around. As an example, none of the grocery stores closest to where I live here in Colorado carried it, including the Safeway store that is within walking distance. But I finally found it at a large Safeway store in Boulder (about a 20 minute drive from home). It is funny how some carry it and others don't. Anyway, you might want to check out some of the smaller, non-chain groceries, or perhaps in locations that tend to cater to the environmentally conscious, or perhaps in older, more traditional neighborhoods.

  9. #9
    Bruce Osgood's Avatar
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    Do not confuse A&H Baking Soda and Washing Soda.

    I use A&H Washing Soda, bought at the local market, as a one to one replacement to Sodium Carbonate mono hydrate in photo chemistry. I've not experienced a problem I would identify with Sodium Carbonates' miss use.

  10. #10
    Peltigera's Avatar
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    In the USA, sodium carbonate is usually mono-hydrate. In the UK, it is usually deca-hydrate when packed. But neither is stable with time. In a warm, dry atmosphere, the deca-hydrate will lose moisture to become mon-hydrate. In damp conditions, the mono-hydrate is likely to pick up some water.

    If it is clearly crystalline, it will mostly be deca-hydrate. If clearly a powder, mostly mono-hydrate.

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