In the first place, that appears to be a formula for subbing cellulose nitrate base not cellulose acetate. Also, the concentration of the Acetic Acid is not specified. I assume it is glacial AA. Heating too long or too hot will denature the gelatin.

Acetone should be free of ALL contaminants. It should be chemically 100% Acetone and not have any denaturants.

If you can get a better formula and better acetone, you will be better off. That formula is close to the ones I have seen though. Gelatin, AA, some plastic and a solvent. I'll take a look at my formulas here, but no promises. Everything I have worked with was presubbed.