On Feb 11, 9:44, Joe wrote: (or produced No, it's not, and never was. There's practically no reaction at room temperature and pressure. In fact it's very easy to turn SO3 back into SO2 and oxygen. Just leave it alone for a while. In the normal "Contact process", SO2 is passed over a catalyst at about 500 deg F, usually VO5 (Vanadium Pentoxide, not hairspray) commercially, or occasionally platinum (in demos) because it *doesn't* normally react with oxygen. The SO3 is then dissolved in concentrated sulphuric acid (H2SO4) because it doesn't dissolve very rapidly in water, particularly when warm, and and the heat of solution would boil water. The concentrated sulphuric acid becomes fuming sulphuric acid ("oleum", H2S2O7) and cold water is continuously added to reduce that to concentrated sulphuric acid again. The other practical[1] method uses very hot concentrated nitric+sulphuric acid as an oxygen carrier -- again, because the oxidation of SO2 is too slow and the activation energy would be far too high otherwise. The SO2, at about 500 deg F (again) combines with NO2 (from the nitric acid) and water to give H2SO4 and nitric oxide; the nitric oxide is then re-oxidised to nitrogen dioxide, which in water gives nitric acid again. Now all you have to do is separate the two acids. [1] Perfectly practical providing you have some concentrated nitric acid, a whole lot of stainless steel tubing, a couple of lead vessels (this process is called the "lead chamber process") and a tower built of acid-resistant bricks, and a water cooling tower. not There's not much in a battery. The equivalent of about 1/4 teaspoonful of sulphur at most, and I suspect, much less. -- Pete Peter Turnbull Network Manager University of York