Well, then, let me ask another question about glycerol. Is Metol soluble in glycerol? I would expect to find the Metol base to be soluble as it is in propylene glycol, but the H2SO4 is a problem. However, I find what appears to be solution of Metol in glycerol when temperature is raised to about 250 F, and remain dissolved as temperature returns to 20 C. I am guessing that a glycerol sulfate is formed that is soluble in excess glycerol.
BTW, when I am raising these temperatures, I do it a bit at a time. There appears to be a threshold above which solution occurs. I can dissolve 10 grams of Metol in 6 fl. oz. of nearly anhydrous medicinal grade glycerol and still have room for 10 grams of ascorbic acid.