I think you misread the graph. Hydroquinone, sulfite and ascorbic acid are treated separately. There is no effect of hydroquinone on the development by metol at any concentration of hydroquinone that was tested, as you can see by the fact that the empty triangle symbols fall on a straight horizontal line originating at the 0 concentration point. The development by metol is accelerated by either ascorbate or sulfite.
Originally Posted by Photo Engineer
The reaction products of hydroquinone accelerate development by hydroquinone, according to the same reference. Ascorbic acid "tames" hydroquinone.
I did what I promised. I mixed a solution of borax, metol and hydroquinone. A snip test of HP5+ with this solution yielded a density above base of 1.3 after 2 minutes at 70 F. I added 3.5 grams of sodium sulfite (anh) to this solution and got a snip test density of 3.04. I added the molar equivalent of the sulfite, 4.9 g, of ascorbic acid converted to sodium ascorbate by 2.45 g of NaHCO3 in a small amount of water. I let the effervescence subside before adding it to the other ingredients. The snip test from this solution measured 3.03 density. I then prepared a solution of metol, borax and sodium ascorbate in an amount equivalent to 6 g of the acid, with the same amounts of metol and borax as the original solution but no hydroquinone. The snip test measured 3.02 density.
I developed a strip of pictorial negatives, all taken from the same roll of the same scene, in each of the three solutions for 8 minutes at 70F. There were slight differences in contrast, about as one might expect from the differences in snip test density. The grain in 10X enlargement is quite good.
I will give a more complete report when I can get around to scanning the prints from each concoction.