From: Sandy King (sanking@hubcap.clemson.edu)
Date: 05/26/00-11:12:50 PM Z
Dave,
It has been my experience that one can substitute potassium carbonate
for sodium carbonate in most developer formulas without changing the
characteristics of the developer. For example, 10 parts of a 10
percent solution of sodium carbonate will give a pH approximately the
same as 1 part of a 100 percent solution of potassium carbonate,
other things being the same.
You may have noticed the Pyrocat formula that was published in the
last issue of Post Factory. The formula there calls for a B solution
of 10 percent sodium carbonate and the working solution was diluted
one part A + ten parts B plus 100 parts water. After the article
came out I changed the B solution to potassium carbonate (to get a B
percent solution of 100%) and now use a dilution of one part A + 1
part B + 100 parts water. The pH of working dilutions made from the
two solutions is virtually identical, as are negatives developed in
them.
I have read that potassium carbonate offers better buffering than
sodium carbonate, especially the crystalline form. This is the form
recommended by Crawley for his FX-2 formula. However, if this is true
I am unable to notice the benefit in my work.
Sandy King
>I have a formula that uses potassium carbonate. Can I use sodium carbonate
>instead? The purpose of the salt in that formula is mainly to set pH. How can
>I calculate the amount needed?
>
>I know I can calculate the conversion with molecular weight, but will that
>give me the same pH? How can one calculate the conversion to maintain the
>same pH?
>
>Thanks in advance!
>
>Dave Soemarko
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