Sodium Bisulfite > Sodium Metabisulfite

OP
OP

Bruce Osgood

Membership Council
Member
Joined
Sep 9, 2002
Messages
2,642
Location
Brooklyn, N.Y.
Format
Multi Format
juan said:
I've used the metabisulfite as a direct gram to gram substitute with no problem. Maybe a chemist can tell us the real story.
juan
Click to expand...

Thanks Juan,
I'll go with 1 to 1 until I hear otherwise. Thank you,
 

Ryuji

Member
Joined
Jan 15, 2005
Messages
1,415
Location
Boston, MA
Format
Multi Format
Why do you say that? When dissolved in water, metabisulfite forms bisulfite ion and they are the same thing. In amateur darkroom formulae I doubt anyone ever used pure sodium bisulfite in dry form as an ingredient; it's a misnomer.
 

Ole

Moderator
Moderator
Joined
Sep 9, 2002
Messages
9,244
Location
Bergen, Norway
Format
Large Format
In solution, they're identical.

There's a difference in the crystal structure, but that doesn't matter at all as soon as it's dissolved.
 

Robert Hall

Member
Joined
Aug 18, 2004
Messages
2,033
Location
Lehi, Utah
Format
8x10 Format
Thank you for the clarification. It was my understanding that Metabisulfite had a lower ph, is this not true?

thx
 

Gerald Koch

Member
Joined
Dec 14, 2004
Messages
1,662
Format
Multi Format
When Kodak sold chemicals a mixture of sodium bisulfite and sodium metabisulfite was sold as sodium bisulfite. If you look at the MSDS for sodium bisulfite it is listed as 58 - 99% sodium bisulfite and 0 - 42% sodium metabisulfite. Pure sodium bisulfite is sold as a 40 - 45% solution rather than as a solid.

Kodak recommended using the same amount regardless of which chemical the formula mentioned.
 

dancqu

Member
Joined
Sep 7, 2002
Messages
3,649
Location
Willamette V
Format
Medium Format
Robert Hall said:
It was my understanding that Metabisulfite
had a lower ph, is this not true?
Click to expand...

There is no metabisulfite in solution. None we be
brewing. At crystallization two bisulfites join loosing
a molecule of water; so the meta. In solution the meta
joins with water; so two bisufites. The meta is more
concentrated by one molecule of water.

Likely there is a source for one and/or the other.
The ph in solution is that of the bisulfite. Dan
 

Ryuji

Member
Joined
Jan 15, 2005
Messages
1,415
Location
Boston, MA
Format
Multi Format
dancqu said:
There is no metabisulfite in solution.
Click to expand...

Not that it matters a lot in terms of darkroom mixology, but this is simply untrue. In concentrated solution of sodium bisulfite, metabisulfite is present.
 

dancqu

Member
Joined
Sep 7, 2002
Messages
3,649
Location
Willamette V
Format
Medium Format
Ryuji said:
Not that it matters ... but this is simply untrue.
In concentrated solution of sodium bisulfite,
metabisulfite is present.
Click to expand...

"None we be brewing" I did qualify my statement.
Besides you and I know better. Concentrated
solution or not, as a species metabisulfite
will exist at ten to the minus who knows
how many zeros. Dan
 
You must log in or register to reply here.
Menu
Log in
Register
Cookies are required to use this site. You must accept them to continue using the site. Learn more…