A month ago I made up a 5lt pack of XTOL to double strength (ie 2.5 lt). I had the water temperature at about 80-90degF and had no problems getting the powders to dissolve. I did this more as a precautionary measure against the possible bad keeping properties that I read about.(posted 8228 days ago)On the idea of keeping A and B in separate bottles, I suspect its a bad idea. As mentioned above, A would probably oxidize without the preservative in B (although someone from Kodak would probably have to confirm that there is no preserving agent in A). I presume the two portions exist due to solubility and pH levels. Chemicals in A may not dissolve as easily in the pH created by B and therefore need to be disolved first.