Bill C , May 20, 2005; 07:54 p.m.
>> Are the two interchangeable? <<
Hi Duane; no, they are not really. If you only needed sulfite ion in solution, you could make a weight adjustment and match up the molar amount (both of them will supply sulfite ion). However, the solution pH will be somewhat different and this often affects us in photography.
Generally, you would stick to sodium sulfite in a developer. If you had something where you needed to hold the pH lower (like a fixer or bleach-fix, etc), it might be convenient to get some or all of the sulfite ion from sodium bisulfite. This could save you from having to add a pH adjuster. A mix of the two could function as a pH buffer in the general range of pH 6.5 to 8 or so. A higher proportion of sodium bisulfite gives the lower pH, while a higher proportion of sodium sulfite gives the higher pH.
I haven't seen the book, but I suspect that if you look at those developer formulas more closely, you'll find that either the one with bisulfite has lower activity, or a pH adjustment is made in one of the developers.