Update from Sandra :

These film canister rockets work just as well with vinegar and bicarb of soda, and that would be a lot cheaper than buying all those alka-seltzers (and look better on the receipts for my guide holiday!!) It works really well, although it is a bit more messy than the alka seltzer ones! If anyone's interested... Make sure you have the film canisters where the lid goes *inside* the can - Fuji do them, and possibly other film companies too. Some of the APS canisters are like this too. Just put about a quarter of an inch (half a cm) of vinegar in the film canister followed by a large pinch of either bicarbonate of soda or baking powder (there wasn't any noticeable difference between the two). You can give it a *quick* shake if you want but it's not needed. Put the canister down lid downwards and stand well back. IF you haven't shaken it then it takes about half a minute to go off but when it does you surely know about it!! Warning: have some water ready for rinsing clothes and/or eyes if they need it, as well as for rinsing the canisters for re-using, they get yucky with the froth. Other warning: don't use as much stuff as you do with the alka seltzer ones or it goes off in your hand and you get soaked with vinegar and bicarb... believe me, I know ;-) Happy fireworks night!