This formula appears in Modern Photographic Processing (Grant Haist) Vol. 1. in the context of low contrast development. The formula is attributed to Silom Horwitz (1967), based on Marilyn Levy's studies of the superadditivity of Phenidone and Pyrogallol.

Stock solution (1L):

1g Calgon
40g Sodium Sulfite
6g Pyrogallol
2g Phenidone

The working solution is a 1+1 dilution of the above stock solution. Development time at 68F was 10min for Kodak Plus-X, rated at ISO speed. It was recommended only for high contrast subjects requiring low contrast development.

I suspect the Calgon could be eliminated if distilled water is used for mixing/dilution.

This has been on my list for a while in my ongoing "survey" of purported low gamma and high speed/low gamma developers. I'm curious to try it, although dissolving 2g Phenidone is a pain. Perhaps I'll mix the working solution (halving all amounts) as a one-shot.

If anyone out there has already tried Horwitz D-512 with any current films I'd be curious to hear about it.

Michael