PS. A small pinch of sodium ascorbate would be even better, as it restores oxidized Metol to its original form without forming the sulfonate, according to what I have read. Anyway, it might be worth considering if the Metol is very old.
just to make sure I understand correctly, you're suggesting the following order (e.g. for D76)...
1) a pinch of ascorbate (would Ascorbic acid from the health food store also work?)
2) the metol
3) the Hydroquinone (?)
4) sulfite (or, Borax...or does it even matter at this point?)
No it's correct. Sodium Metabisulphite is often used in small quantities in developer formulae. In theory if you use bisulphite instead you should add slightly more as it's not quite the same. I found a Kodak research article recently in a BJP Almanac (late 40's/early 50's) that compared the two and gave the suggested equivalents, the book's in the UK but I may have scanned the article. The difference is generally around 3-4% more Bisulphite is need compared to Metabisulphite.
I have 6 other film developers in my database using 0.13 up to 1 gram per litre of film developer, these are Ilford, Crawley and Agfa Ansco developers, (4 are 0.5g or less).
The importance of the metabisuphite is the free SO2 it gives off, it's often used to stabilise commercial powdered developer - used in Part A with the developing agents.
In fact, if you run out of hydroquinone, you can try this: multiply the required amount of hydroquinone by 1.6 to find the amount of ascorbic acid. Multiply that amount to get the required amount of baking soda. Mix these amounts in water , Use a big container,but not any more than half the water you're going to use to make the developer. It's going to fizz a lot. When it quits fizzing, dissolve the Metol, then anything else that needs to go in and enough water to bring the volume up to total. You can try this sometime when you have time to play. It will substitute about the same number of molecules of sodium ascorbate for the hydroquinone.
BIG BOO BOO!
Multiply the calculated amount of ascorbic acid BY 0.48 to get the amount of baking soda. By baking soda I mean, of course, sodium bicarbonate like you take for bellyaches such as I sometimes give people.
Maybe Metol available in the 30's did have a possible oxidized component. Oxidized Metol is a development inhibitor. Sulfite converts it to the sulfonate, which at least is a weaker developing agent. Hydroquinone + sulfite regenerates oxidized Metol, as does an ascorbate. If their method is no longer needed, it still might do some good and no harm. There is no appreciable increase in time required for preparation.
become with powdered commercial developers, acts like any
sulfite to preserve. Why the BIsulfite is still a mystery. Free
sulfur dioxide, sulfite or bisulfite, is unlikely because it
would take quite an acidic environment to cause it's
release. Over acidic stop baths can cause it's
Metabisulphite is used to control the pH, the SO2 forms sulphurous acid in solution, in combination with Sulphite it also has a buffering effect.
The Sulphite/Metabisulphite buffer range is between pH 8 and pH 6.5, becoming more acidic as the proportion of Metabisulphite is increased, this is compared to the Borax/Boric Acid buffer range of pH 9.2 to pH 8.
As a preservative Metabisulphite is many times more effective than Sulphite., which is why it's used in the food trade and wine making.