Re: Paper makers... Sizing and Buffering... repeat question

About this list Date view Thread view Subject view Author view

From: Ryuji Suzuki (RSuzuki@MIT.EDU)
Date: 01/14/03-09:13:54 PM Z


From: John Glen <microcrystals2002@yahoo.com>
Subject: Re: Paper makers... Sizing and Buffering... repeat question
Date: Tue, 14 Jan 2003 01:39:19 -0800 (PST)

> I am wondering what you think about X's (Sorry, I
> don't have his name with me at this moment)claim that
> the octahydrate is a misnomer and that the substance
> in question is actually the tetrahydrate.

This is X (probably).

Although there's a very good reason to believe sodium metaborate
commonly available is either tetrahydrate (called octahydrate in old
literature but they refer to the same compound in the same actual
hydration -- they are denoted in different ways) or unspecified mixed
hydration, it is not likely to matter much for most photographic
purposes unless your application is very sensitive. Changing hydration
is equivalent to changing the amount of the dry metaborate you use, so
you can determine your right amount experimentally.

I'm not familiar with your project and can't give you a specific
answer but if you want pH 9 to 9.2 range, borax is an agent that gives
you a good buffer whose pH is relatively independent of
concentration. (That is, even if you use too much borax, the pH won't
be much above 9.) Metaborate does not have this property - their pH
varies quite a bit with varying concentration. If carbonate buffer is
suitable for your application, you can make a good buffer for a target
pH in a range from 9.5 to 10.5, maybe a bit wider range, by mixing
sodium bicarbonate and sodium carbonate at different proportions.

In a range below 8.5, phosphate or triethanolamine is a good buffer.

Choice of buffer should be made with your target pH and compatibility
with your applications. Again, I don't know what your project is, so I
can't be much more specific.

> I use one of the metabisulfites for sterilization of
> bottles home made Root Beer... (any other brewers out
> there?)and I have a bottle of Sodium Hydrogen Sulfite
> I use for developers...seems like they are sort of the
> same thing...

One mole of metabisulfite makes two moles of bisulfite ions in water
unless you are making a very concentrated solution. But this is a
different problem from metaborate hydration issue.


About this list Date view Thread view Subject view Author view

This archive was generated by hypermail 2.1.5 : 02/21/03-10:44:16 AM Z CST