View Full Version : difference between monohydrated and anhydrous

18-Jul-2008, 14:09

I finally ran out of my stock of Kodak Sodium Carbonate(don't remember whether it's mono or anhydrous), while trying to order them from Photographer's Formulary, I found they have both. Can one be use for the other? what is the difference between them?

Artcraft just carry one of them, the mono version.

thanks in advance


18-Jul-2008, 14:17
The monohydrate contains one molecule of water per molecule of sodium carbonate. I can't see that it would make much difference in actual use.

18-Jul-2008, 14:39
The Beer formula calls for monohydrated, does that mean the monohydrated is not completely desiccated?

18-Jul-2008, 14:49
No, it's dry and crystallized, but it has one water of hydration. Normally, you'd just account for the extra water of hydration in weighing out chemical (it weighs a little more with the H2O molecule) for precise uses, but I highly doubt it would make the least bit of difference in your formula. But I'm a biologist, so I fully expect a smackdown from a chemist. :)

18-Jul-2008, 14:55
:) well, I am just a darkroom alcoholic so it's deserving to get a full smack down from both the biologist and chemist

Thanks for the clarification, I'll just go with what ever is the least expensive:D


19-Jul-2008, 08:46
Actually the Beers formlula calls for anhydrous Sodium Carbonate, it's just hat some US publications convert and list as Monohydrate instead. Others (Anchell) list it with Potassium Carnbonate but that give a slight tone change.

The ratio of Monohydrate to Anhydrous is approx 1.17 : 1 The anhydrous form is most coomon, (in Europe) followed by the crystalline form.


20-Jul-2008, 10:21
A significant difference between the two is that the monohydrated form dissolves much quicker. The anhydrous form can be substituted for the monohydrated form: as noted above, 1 part of the anhydrous form = 1.17 parts of the monohydrated form. To illustrate: Ansco 103 calls for 78.0 grams of the monohydrate. When using the anhydrous form instead, use (78.0/1.17) ~ 66.7 grams.

N. Riley