I heard about this in my chemistry class and have been wanting to try it for months. A friend and I finally were bored enough to do it today. We went to a pool supply store and bought a gallon of muriatic acid. Then we bought some aluminum foil. Take an empty bottle.. we found that small 20oz plastic bottles work best and use less acid. Pour about an 1/8th to a 1/4 of the bottle full of the acid and stick a piece of aluminum foil in the bottle and cap it. Shake it up to pressurize it. You will feel it get Hard and eventually Hot but don't hold it very long. Once its hard Throw it! It'll either cause a loud large explosion when it hits the ground or the bottle will hit the ground and began expanding and eventually explode. Its very loud and VERY FUN!!! The bottle is almost completely destroyed. A yellowish black liquid will bubble on the ground. Make sure the cap of the bottle is on very tight otherwise the substance will just leak out of the bottle and no explosion will happen. I also recommend wearing gloves or having water nearby. The acid can burn. It didn't bother my hands but my friend's hands turned red and irritated him. It's a fun and cheap way to pass the time. The acid costs about $3-$4 for a gallon. You can get a lot of explosions out of a gallon of the acid. Have fun!