Quote Originally Posted by john_s View Post
I'm thinking of trying D316. I have two questions.

1. If I use a bit more propylene glycol, say to make 25mL of concentrate instead of 20mL, will that make it easier to dissolve and less likely to crystallize, or will the different concentration of metaborate alter the solubility of the ascorbic acid? I would obviously use 25mL of the concentrate to make 1_L of working solution.
Good to hear that!

I think that boosting the propylene glycol (PG) will make it easier to dissolve the powders. But at the temperatures I gave, everything dissolved in a reasonable time, and comfortably below the crystallization-point. Boosting PG will have a small effect on the developer, as it reduces pH a tad. But I doubt the difference would be significant.

Quote Originally Posted by john_s View Post
2. Whichever version of sodium metaborate I have, it shouldn't make any difference, should it? In my post above where I pasted Ryuji's comments about the naming of sodium metaborate (tetrahydrate and octohydrate) although the theoretical compositions of the two compounds give very different molecular weights (one double the other) it seems to me that 2.2 grams of either is exactly the same when dissolved. I have bought chemicals from a supplier who has been generally a bit slack with noting water of crystallization, which usually makes a difference but not, I think, in this case. It's been a while since I did high school chemistry (1965).
Actually, the kind of metaborate will make a substantial difference, because the number of moles of the anhydrous form (i.e., NaBO2) in 2.2 grams will differ. For 8-mol metaborate, you'll need 3.0 grams. If you have a pH meter, you can mix the ingredients directly into water (including the PG) and see if the pH is around 8.08.

Without a pH meter, you could mix the concentrate using 2.2 grams, and see how long the ascorbic acid takes to dissolve at 75C (assuming 20 ml of PG). If it takes longer than 5 minutes to dissolve most of it, then you probably have the 8-mol s.metaborate, and will need to add another .8 grams of it. Alternatively, you could mix the concentrate using 20 ml of PG and 3.0 grams of metaborate, but at a temperature of 85C for everything. If it crystallizes (white marks on bottom of beaker and then cloudiness), then you know you should start over with 2.2 grams.

Good luck,

Mark Overton