I've been using Kodak sodium carbonate, mono, but now I've chiselled the last of it from the jar and I have a 5 pound plastic jug of 'Sodium Carbonate'. Doesn't say which kind. How can I tell? I inherited the chemical. It is probably 10 years old. It is a little cakey, but not as hard as the jar I was using.
No clue really, but if you are going to use it in a print developer I would assume it is anhydrous and if you get the results you did from using the previous carbonate then you are OK. If the prints take longer to come up you probably have the mono version and if my memory serves me right from a previous post multiply the amount by 2.3
Hope this helps
Monohydrate is the most stable form, so that's my guess... It takes 20% more monohydrate than anhydrous to do the same job. "times 2.3" would be about correst for heptahydrate, which gives up some of its water at 32°C. Easy to spot: Looks like it's melting at body temperature...
I wouldn't fool around with 10 year old cakey chemistry. Whatever caused it to become cakey is not going to be of benefit when using it.
I've switched to Arm & Hammer Super Washing Soda, it is all Sodiulm Carb - Mono with no perfumes or phosphates. It sells for about $2.30 for a 55 Oz. box and is available in almost any grochery store. Just make sure it is washing SODA, not degergent.
If it is washing soda it is not monohydrate nor is it anhydrous. Washing soda is the official common name for the decahytrate. That is why you must use 2.3 times as more by weight than the monohydrate, or 2.7 times more than the anhydrous.
If you are not sure what you have, you can heat the heck out of a weighrd sample of it. If it loses weight it was not anhydrous. If 270 grams shrinks to 100, it was washing soda. If 124 grams shrinks to 100, you have monohydrate.
I'm sure you can do the arithmetic for other amounts.