Soap Dispenser Question

This isn't, strictly speaking, a home repair question but someone here will likely know.
On those commercial restroom hand soap dispensers, the ones where you pull or push a lever and instead of getting an amount of liquid soap you get a blob of foam, what makes the foam? What gas is in the tiny micro bubbles, air? It's liquid in the container so how is it turned into foam? Can you make liquid into foam just by forcing it through a nozzle?
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On Mythbusters they pumped hydrogen though soapy water. A column of foam floated up, which they then lit. I guess you had to see it.
No idea what makes the soap foam up like that, but I don't like it myself.
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The valve mixes air with the low-viscosity soap. I don't know the technical aspects but you can buy a Dial Complete foam pump at the grocery store and take it apart to try and figure it out.
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