Water content of Arm & Hammer washing soda?

walbergb · Jun 25, 2012

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.

F/1.4 · Jun 25, 2012

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

Gerald C Koch · Jun 25, 2012

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

Denverdad · Jun 25, 2012

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.

ezwriter · Jun 25, 2012

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

Alan Johnson · Jun 25, 2012

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.

pdeeh · Jun 25, 2012

Rheinhold's Caffenol blog gives some information which may be useful http://caffenol.blogspot.co.uk/2010/03/soda-myth-and-truth_07.html

Denverdad · Jun 25, 2012

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.

Bruce Osgood · Jun 25, 2012

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.

Peltigera · Jun 25, 2012

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.

Peltigera · Jun 25, 2012

F/1.4 said:
I don't know, but usually when I use it to make Caffenol, I'm mixing with water anyway.

It matters as the water content determines the weight to be used.

hrst · Jun 25, 2012

It is probably something between mono and decahydrate.

The only way to REALLY know is to test. There was a thread here in APUG where people reported their test results (or at least I did):
(there was a url link here which no longer exists)

Once you figure it out, maybe you can assume that the different batches with the same label are close enough. Luckily, the amount of carbonate in a developer, for example, does not affect pH that much; it's more about buffering capacity.

ezwriter · Jun 25, 2012

i'm in So Cal, CA area and none of grocery stores carry it. Finally found TSP i think at a home depot.

Prof_Pixel · Jun 25, 2012

I found a couple of MSDS sheets on the web that said A&H Washing Soda is approximately 85% sodium carbonate and 15% water so it sounds like it is the monohydrate

bdial · Jun 25, 2012

TSP is not the same stuff.

As for the washing soda, it seems to have disappeared in the grocery stores here too, but my wife just got some from the local hardware store.

removed account4 · Jun 25, 2012

tsp is tri sodium phosphate

you can convert baking soda to washing soda if you run into a problem
just put it on a cookie sheet and then in an oven low heat for a few hours
the heat will force the moisture out and convert it to sodium carbonate.

Prof_Pixel · Jun 25, 2012

I believe you mean baking soda and not baking power. Baking power contains both an alkaline component (typically sodium bicarbonate, also known as baking soda), one or more acid salts(like Tartaric Acid), and an inert starch (cornstarch in most cases, though potato starch may also be used).

Baking soda is just sodium bicarbonate without all the extras.

Gerald C Koch · Jun 25, 2012

Alan Johnson said:
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.

This is surprising considering the cost of shipping. It is rather inefficient to ship the decahydrate as you are paying to ship a lot of water.

desertrat · Jun 25, 2012

Most hardware stores and most Walmarts have swimming pool chemicals. A common pool chemical known as PH Plus is sodium carbonate, same as the hard-to-get washing soda. It may be the mono-hydrate. I use it to make my developers that use sodium carbonate.

kiku · Jun 27, 2012

Try a wine and beer making supply shop. They will have it as "washing soda" or maybe sodium carbonate. Howard Tanger

Gerald C Koch · Jun 27, 2012

hrst said:
It is probably something between mono and decahydrate.

The last time I remember seeing the decahydrate was in the 1940's. It consisted of large (3/4 to 1 inch) lumps which looked like ice. Soon after the box was opened the lumps began to take on a white powery coating of the monohydrate. Left exposed to the air the lumps eventually dried out to a white powder.

hrst · Jun 28, 2012

Gerald C Koch said:
The last time I remember seeing the decahydrate was in the 1940's. It consisted of large (3/4 to 1 inch) lumps which looked like ice. Soon after the box was opened the lumps began to take on a white powery coating of the monohydrate. Left exposed to the air the lumps eventually dried out to a white powder.

You describe perfectly the product I buy here! It really looks like a mixture of mostly ice and a bit of powdery snow. As I showed in the thread I referred to, it is almost pure decahydrate.

The ratio between "ice" and "snow" seems to vary between batches.

Of course it does not make real sense to ship water, but it makes a LOT of "business sense" to sell water. Think about liquid detergent business... Or, think about liquid photochemistry business!

Water content of Arm & Hammer washing soda?

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