[sbierwagen]

Interesting, though, for DIY, I was expecting him to do it the way Linde did, back in 1894, that being:

  Compress some dry air.
  This will heat it up, so cool it down.
  Return it to atmospheric pressure.

While expanding, it, of course, gets even colder still, and condenses. Liquid nitrogen is old tech, older than you might think.