John Melanson (john@audiologic.com)
Mon, 26 Jul 1999 12:18:47 -0600
> -----Original Message-----
> From: Sil Horwitz [mailto:silh@iag.net]
> Sent: Sunday, July 25, 1999 2:33 PM
> To: alt-photo-process-l@sask.usask.ca
> Subject: Re: sodium metaborate, to make?
>
>
> At 1999/07/25 01:59 PM -0600, Ken Sinclair wrote:
>
> >According to Maxim
> Muir.....<http://www.nfinity.com/~mdmuir/shopping.html>
> >1 part sodium hydroxide : 5 parts borax = sodium metaborate for PMK
>
> It may work in that application, but what you get isn't "sodium
> metaborate"!
>
>
> Sil Horwitz, FPSA
> Technical Editor, PSA Journal
> silh@iag.net
> silh@earthlink.net
> Visit http://www.psa-photo.org/
> Personal page: http://home.earthlink.net/~silh/
>
Actually, it is metaborate you get. Both tetra borate (borax) and
metaborate (kodalk)can be legitimately viewed as formed by aqueous mixtures
of boric acid and sodium hydroxide.
(borax) Na2B4O7 + 7 H2O <-> 2 NaOH + 4 H3BO3
(sodium metaborate) NaBO2 + 2 H2O <-> NaOH + H3BO3
Relative to the boric acid, the metaborate carries twice as much OH as the
(tetra) borate.
To "make" 100 gm sodium metaborate solution,
69.16 gm Borax (decahydrate, 20 mule team) + 14.50 gm Sodium Hydroxide (Red
Devil).
All the disclaimers here about Lye - use with obscene caution, etc.
If you want the crystals, start with hot water, saturate the borax, add the
NaOH (in slight excess), cool.
The crystals will be very pure sodium metaborate.
All the borates are great buffer, you can vary the pH continuously, and
repeatably.
(I've used this formula for PMK B for years, no difference in pH, I've
tested it.)
Happy home brewing!
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