FilmIs4Ever submitted a new resource: Kodak SH-1 Formalin Hardener for Films and Plates - Kodak SH-1 Formalin Hardener for Films and Plates Read more about this resource...

Common Formalin is actually about 37% and the formula I have contains 50 - 100 g/l of Sodium Sulfate. PE

Hey, Ron, so would that require an adjustment of this formula? I assume that they either got lazy and rounded it to 40% or the concentration may have been changed since this was published in 1947.

Actually, my formula used 10 ml/l of 37% formalin and the pH was stated to be 9.5 - 10.1 in the formulas I have in my notebook here. PE

So is the pH for the SH-1, or the formalin soln. you add to it? As is indicated, the formula I have is originally in U.S. Customary, so it's possible they just carelessly rounded to the nearest half fluid dram when they converted it from a formula originally written in cgs units, which accounts for the shift down when I converted back. IIRC, it was actually somewhere in between 9.75- and 10mL, and I just rounded to the nearest 250µL. I'd assume that the formalin is actually the same in both cases and they just rounded to 40% in the book I have. Converting the amount in a 40% solution to 37% gives about 10.5mL equivalent so that isn't the reason for the difference in the amount. Again, it's probably a matter of my formula having less exact rounding than yours does. Is the Na-Sulfate in addition to- or as a replacement for the Sodium Carbonate. I've noticed that there are more than a few examples of Kodak formulae, published by Kodak or allegedly taken straight from Kodak that are modified over time, without any indication.

The pH of the hardener should be alkaline and varies slightly due to the fact that unstabilzed formalin can oxidize to form formic acid as a contaminant. This causes some variation in pH. I used to adjust the pH to the pH of the developer I was using. The sulfate is in addition, not in place of carbonate as the solution should be buffered with an alkali. The hardener I refer to may be a different formula number, it is just the preferred one we used in-house. PE