Help- need chemist on crystal vs anhydrous K2CO3

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I've been fooling with Crawley's FX-2, which seems to have some really nice properties, but I've forgotten most of my chemistry. The conversion from anhydrous to mono Sodium Carbonate is well known, but this formula uses Potassium Carbonate. My old chem handbook lists the formula weights as 138.21 for the anhydrous and 330.47 for the crystalline form with 3H20. Anchell says the crystalline form is 1.5H20 and doesn't give a conversion. Hmmmm. FX-2 uses crystalline, so do I multiply the quantity by .418 if I use anhydrous, or is there another form I don't have a formula weight for? Also, what's this business about a bicarbonate buffer depending on what grade you buy? Does it matter in the developer? Help! I need a chemist.

-- Conrad Hoffman (choffman@rpa.net), February 03, 2002

Answers

Ah-ha! I just found the correct formula for Potassium Carbonate in crystal form. It's 2X on the potassium and 3X on the water, so Anchell's "1.5 molecules of water" is correct. That means my first experiment was pretty fouled up, as I had about twice the amount of carbonate as desired. Now my only question is about the buffer referred to. Is this something that should be added?

-- Conrad Hoffman (choffman@rpa.net), February 03, 2002.

Conrad, Anchell and Troop recommend substituting 150g/L sodium metaborate (Kodalk) for potassium carbonate. I've tried it and it does yield slightly smoother tonality, while minimally reducing the biting sharpness of the original formula.

I've used 8ml of 10% sodium hydroxide /L (instead of 75ml of 10% potassium carbonate) of working developer as the B component and it yields smoother tones and finer grain than either of the above options, and with very high sharpness too.

-- Ted Kaufman (writercrmp@aol.com), February 03, 2002.


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