# Potassium Metabisulfite vs Sodium Metabisulfite



## OMG (Nov 10, 2007)

Has anyone used Potassium metabisulfite as a precipitant in place of SMB?
Thats all I could find around here, so thats what I'm going to use when I get up and running.
Has anyone used it successfully, or had problems with it?


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## Noxx (Nov 10, 2007)

They are mostly the same. 
You can use both with same results.


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## scrapman1077 (Nov 10, 2007)

I use sodium sulfite for gold, works well and its not to hard to get ( fire works supply).


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## goldsilverpro (Nov 10, 2007)

I always used sodium sulfite. The photo grade is quite pure, readily available at large camera shops, and fairly inexpensive.


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## OMG (Nov 11, 2007)

Thanks guys, I'll let you know if anything funky happens.


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## teabone (Dec 11, 2007)

OMG , I've used the potassium before with same results , its the salt that does the work . It works just as well.


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## lazersteve (Dec 11, 2007)

Long time no post Teabone,

How have you been?  

It's good to hear from you. 

It's actually the SO2 produced that is doing the work. From a mass verses the amount of SO2 produced point of view it will take more of the potassium based reagent than the sodium based reagent. 

Steve


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## teabone (Dec 11, 2007)

Lazersteve , I've been around , lurking , as you know I'm not much of a poster , but I do enjoy reading the other posts . I always learn something from you guys . You're right about the potassium salt, you do have to use a little bit more of it for precipitation .


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## alancj (Jan 13, 2008)

Potassium metabisulfite has a molar mass of 222.32 g/mole
Sodium metabisulfite is 190.1 g/mole

So you'll need to use about 17% more (by weight) of the potassium salt to deliver the same effective SO2 as the sodium salt.

-Alan


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## aflacglobal (Jan 14, 2008)

Welcome to the forum Alan.


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## Irons (Jan 14, 2008)

goldsilverpro said:


> I always used sodium sulfite. The photo grade is quite pure, readily available at large camera shops, and fairly inexpensive.



Now that people are going to digital cameras and black and white film is being dropped by suppliers, it's getting harder to find photo shops that carry chemicals. I tried the shops in my area and all they had were a few left over chemicals and they weren't reordering.

There are sources on ebay that sell it for under $2 a pound in larger quantities.


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