Re: "Room temperature"
Exeter Uni's Physics department has it's own gas liquefaction plant out the back, mostly to provide liquid nitrogen, and liquid helium for the research MRI machines. They produce so much LN2 there used to be massive dewars of it sat at the bottom of a staircase, just waiting for any student with a bucket, to come along and help themselves. I was told they sell the liquid oxygen and other interesting gasses to BOC, so it's possible your LN2 might have come from there.
I'll leave it to your imagination to imagine the hi-jinks us undergrads got up to with an easy supply of liquid nitrogen ;)