In order to carry liquid nitrogen, you need a container that provides extremely
good insulation. Liquid nitrogen is more than 320 degrees below zero
Farenheit. This is about 200 degrees colder than it is anywhere on
Earth. Dewars are specially made containers that allow you to carry
things this cold. Unfortunately, getting something (like a dewar) with
such good insulation is inevitably going to be expensive.
Other than expensive dewars, which can keep the liquid nitrogen for
a long time, you can also keep it in just a plain styrofoam cooler of
some kind. This will work pretty well, but since the quality of the
insulation is not quite as good, the liquid wont last as long (it will
probably be "boiling" away the whole time it's in the cooler). If you
are going to try using a styrofoam cooler, make sure you get one whose
sides are as thick as possible, both for insulation and strength (you
don't want it cracking and spilling liquid nitrogen on someone).
If you are wanting to buy a dewar, however, you can save yourself a
lot of money by being careful about where you buy it. For example, if
you buy it from a laboratory supply company that caters to physicists,
it will be a lot more expensive than if you buy it from one that caters
to biologists. I don't know what the economic reasons for this are, but
it can make it a lot cheaper for you.
In general, though, it's not practical for most people to get
liquid nitrogen. However, most anything that you would want to do with
liquid nitrogen can also be done with dry ice, which is much easier to
get and a lot cheaper to store.
(republished on 07/25/06)