You guys didn't understand his query properly. What he is saying is that the pre-reaction mixture of formic acid and H2O2 is being catalyzed by something causing an exotherm of effervescence of O2 gas. The problem is a simple one; it can be one of only two possibilities. Either the formic acid is contaminated or the addition funnel is dirty or has a piece of a foreign substance in it that can catalyze decomposition of peroxides/peracids. Even though you cleaned the additional funnel out thoroughly, it may be the culprit because metal oxides from the stopcock clip may have worked themselves up into the funnel or stopcock joint. The way to determine if the funnel is the guilty party is to fill it with plain 30% peroxide and watch it for a few hours to see if it starts to decompose(bubbles- not a few bubbles as thats normal, we're talking about vigorous effervescence). Make sure you twist the stopcock around a few times so the peroxide is exposed to any catalytic materials possibly stuck in the joint. If the plain peroxide does not bubble, than the problem is obviously contaminated formic acid. Chances are the mystery catalyzing substance dissolved in the formic is not an organic chemical, rather a transition element salt from a previous storage container. You have no way of knowing what the formic was stored in before it was rebottled and sold to you, neither do you know what kind of equipment was used to transfer the bulk liquid into the smaller bottles for retail sale, therefore metal salts could have easily been deposited/dissolved into the acid resulting in your conundrum. The easy solution is to distill the formic acid at STP using scrupulously cleaned glassware. Report back and let us know which of my guesses correct!
