Sodium Sulfite, Sodium Bisulfite, and Sodium Metabisulfite

[Donald Miller]

Are any of these chemicals interchangeable in developer formulations? If so what are the relative amounts used in substitutions?

 

[john_s]

Ryuji Suzuki has an informative article on the interchangeability of the bisulphite and meta bisulphite at:

http://silvergrain.org/Photo-Tech/chemistry-misnomers.html

The sulphite is different.

 

[sanking]

Yes, to some extent. Both sodium metabisulfite and sodium bisulfite are acidic and are used as a preservative in many two part developers (PMK, Pyrocat-HD, Rollo Pyro, etc.) In this application plain sodium sulfite is not interchangeable with metabisulfite and bisulfit.

However, when dissolved in water (as in a working solution) both sodium metabisulfite and sodium bisulfite release sulfite ions. On a per gram basis, in this type of application, the ratio is about 13:10 sodium metabisuflite to sodium sulfite.

But see Ryuyji's web page mentioned above for a more detailed discussion of the subject.

Sandy

Are any of these chemicals interchangeable in developer formulations? If so what are the relative amounts used in substitutions?

 

[Donald Miller]

Thanks for the information. I will check it out.

 

[dancqu]

Are any of these chemicals interchangeable
in developer formulations? If so what are the
relative amounts used in substitutions?

They are all interchangeable only if the formula
so states. Other wise only the two bisulfites
are interchangeable.

The two bisulfites are acid salts and the same save
for the meta form being short one molecule of H2O.
That is due to the loss of one H2O at the time of
crystallization. Just add water and you've the
bisulfite; Na2S2O5 + H2O = 2, NaHSO3.
Strictly speaking the meta is a bit
more of a concentrate.

The sulfite is moderately alkaline while the bisulfites
are moderately acid. They are all sulfites and so do act
as preservatives. I've some phenidone concentrate
using sodium bisulfite. Generally, an acid solution
of a reducing agent will preserve better than
an alkaline solution of same. Dan

 

[dancqu]

However, when dissolved in water (as in a working solution)
both sodium metabisulfite and sodium bisulfite release sulfite
ions. On a per gram basis, in this type of application, the ratio
is about 13:10 sodium metabisuflite to sodium sulfite. Sandy

The meta is not a bi nor a sulfite; Na2S2O5. Meta means
a form more nearly anhydrous or lacking some water. Similar
are the acids of boron, ortho, meta, and tetra. We use
the sodium salts metaborate and tetraborate.

By weight 190 parts of the metabisulfite equal 208 of the
bisulfite. In solution the meta will hydrate, absorb H2O,
and transform into a bisulfite.

IIRC there seems to be some question as to what is
in the bottle. Some years ago I read Ryuji's writings on
the subject. He covers the subject in more detail. Dan

 

[sanking]

The meta is not a bi nor a sulfite; Na2S2O5. Meta means
a form more nearly anhydrous or lacking some water. Similar
are the acids of boron, ortho, meta, and tetra. We use
the sodium salts metaborate and tetraborate.

By weight 190 parts of the metabisulfite equal 208 of the
bisulfite. In solution the meta will hydrate, absorb H2O,
and transform into a bisulfite.

IIRC there seems to be some question as to what is
in the bottle. Some years ago I read Ryuji's writings on
the subject. He covers the subject in more detail. Dan

I have visited Ryuji's site and am aware of the the meta versus bisulfite issue.

As for the ratio of sulfite ions released by sodium metabisulfite when dissolved compared to sulfite ions from sodium sulfite when dissolved, I believe that is correct.

Sandy

 

[Ryuji]

Since my web site got mentioned... I'm in process of converting old static html based technical info pages to Wiki system similar to wikipedia. It's a lot easier for me to edit and update articles this way. (It's also easy to start writing something and expand later.) So when the link for old stuff goes away, try to search by keyword in the wiki page.