Measuring Sodium Carbonate

[ronlamarsh]

I use the teaspoon method and washing soda for my sodium carbonate. Is washing soda monohydrated or anhydrous?

 

[BradS]

almost certainly the monohydrate form as it is the most stable. The anhydrous will such water from the atmosphere and eventually become mono.

 

[Ian Grant]

Washing Soda is usually Crystalline, not mono-hydrated - well in the UK anyway.

The ratios are 2.7 Crystalline, 1.17 Mono-hydrated, 1 Anhydrous

Ian

 

[dpurdy]

A few months ago I ran out of sodium carbonate at the same time the photo store did and I went to the grocery store and got a box of Arm and Hammer Super Washing soda. I was a bit skeptical as it has kind of a pretty smell. But I used it in both paper and film developers and I don't see anything different from the expensive stuff. Now I bought my second box and measure it by pouring it out of the box into a small graduate.

 

[Anscojohn]

I snail-mailed Arm and Hammer about this years ago. IIRC, the gal who wrote to me seemed a bit evasive, but said she checked with their tech people who told her that if their Washing Soda is left exposed to air, "it tends to the monohydrate." I inferred, therefrom, it is crystaline, and have always treated it as such.

 

[jim appleyard]

I've always used as crystalline. In fact, I mixed up some D2D out of the Cookbook with A&H. When used as crystalline, D2D works fine, but mixed as mono, I got very thin negs.

Bear in mind that my darkroom is in my basement, not dry, but I'm not standing in water either! I think my washing soda has plenty of humidity to suck up.

 

[gainer]

Weigh some of the washing soda into a pyrex cup and heat it in the oven at about 150 F for a while. The result after an hour ought to be pretty near anhydrous. Weigh it again. You can tell by the amount of weight loss whether it was originally true washing soda, the monohydrate or the anhydrous. Washing soda is oficially the decahydrate. 286 grams of it will make 106 grams of anhydrous. 124 grams of the monohydrate will make 106 grams anhydrous. There is also a heptahydrate. 232 grams of it will make 106 grams of monohydrate.

What it amounts to is that if you don't know what you have, heat it enough in an open container and you will have the anhydrous stuff. It will "tend" toward the monohydrate, but it will take a long time to get there if you keep it in a closed container

 

[Mike Wilde]

Arm and Hammer seems to put 'something fragrant' in thier 'not advertised as scent free or scented either' washing soda.

I use this all the time to mix up Agfa 100 or D72 print developer, and treat it as monohydrate, whether this is right or wrong.

I mix the developer and store it in old 1L Ilford while plastic developer bottles I have accumulated prior to mixing my own developer. After a day or two, the 'gunk' in the washing soda coagulates and floats to the top of the storage bottle. If the bottle was filled properly to the right level, then the plastic bottle can be squeezed, and this crud can be flicked off the surface into the drain like cream was once cut off of th top of whole raw milk.

I top the developer off in the 1l bottle if I am not going to use it right away, or pour half of the litre into a 11x14 tray, diluted 1:2, and store the remainder of the litre in another surplus and reclaimed 500mL plastic Ilford container. The scent can sometimes be smelled in the finished print, but few ever get that close to one of my prints.

I know that developers last longer in glass, but this is print developer, and mixing it this way it is so cheap it is not worth the hassle of scrubbing the fleks of crud out of glass bottles.

 

[gainer]

It's better IMO to get the carbonate that is sold for spas and swimming pools, called pH Plus by one manufacturer. It is at worst monohydrated. It does not contain pretty odors or water softeners. If you heat it, you'll get the anhydrous. For many recipes, the difference between anhydrous and monohydrated is not significant.

 

[BradS]

cooking ordinary baking soda (in an oven at 350degrees F for about an hour per pound, stir every ten minutes or so) also produces a very pure Sodium Carbonate and, of course, it is the anhydrous form when it comes out of the oven