|Is there any way to make a homemade fog machine, like they use in clubs? — JW, Westport, CT
While it's pretty clear that fog machines fill the air with tiny water droplets, I'm not sure how all of them work. Some probably use high-frequency sound waves to break up water into tiny droplets and then blow these droplets into the room with a fan. That technique is used in some room humidifiers and you can see a stream of fog emerging from them as they operate. An easier way to make fog is to mix water and liquid nitrogen. While liquid nitrogen is harder to find, all you have to do is put them together and they'll start making fog. The boiling nitrogen shatters the water into tiny droplets, which flow out of the mixture in a layer of cold nitrogen gas.