Kodalk?

[fotomas]

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Hello,

I'm searching for Kodalk / Kodak Balanced Alkali. All marks I found say that it's sodium metaborate. But which substance in particular?
Here the possibilities:

CAS-Nr.,       Name                                               Molar mass

7775-19-1   Sodium metaborate,                           65,798
16800-11-6 Sodium metaborate-dihydrate,          101,828
10555-76-7 Sodium metaborate-tetrahydrate,     137,858
35585-58-1 Sodium metaborate-octahydrate,      209,918

Depending on the literature some say tetra-hydrate, other say the octa-hydrate is Kodalk.

I would also assume, that is one of these both, but which one?
Hope there is someone who can tell.

Also I found a lot off different formulas how to create sodium metaborate with borax and sodium hydroxide or with boric acid and sodium carbonate. Would be nice to have a valid one.

Best regards

Frank

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[adan]

This site says "Sodium Metaborate, octahydrate (8H20), and Balanced Alkali (Kodalk) are for all practical purposes the same thing. Subsititution can be made weight for weight."

They also sell it...

https://www.bhphotovideo.com/c/product/124067-REG/Photographers_Formulary_10_1285_100G_Sodium_Metaborate_Balanced_Alkali.html

Edited August 27, 2020 by adan

[fotomas]

Thanks Adan,

I also found this site. But there are also others that claimed it should be the tetrahydrate. But meanwhile I found the solution by myself. On the cover of the Darkroom Cookbook there is a picture of some lab stuff. One is a Kodak bottle of Kodalk. With a magnifier I could read the CAS-number written on the label. It was 35585-58-1, and so it really is the octahydrate.

I'm in Europe, so I guess I can't order it from here. But they also give a hint, how to mix it yourself with borax and sodium hydroxide. But here confusion continues. I found different ratios to mix it up from 1:4.25 up to 1:4.78.
Got the impression, that the pH-value of the formular given there is a bit to low (pH = 10.4 for a 10% solution).

In the end it also seems that for the dry salt even two CAS-number are around, 98536-58-4 and 7775-19-1.

Best

Frank