This is a followup of sorts to a question that arose last week regarding
the use of nitrogen gas in aerosol cans.
From the September 1, 1990 edition of "Breakthrough", which is a
supplement to the newsletter "Privileged Information":
SAFER AEROSOL CANS:
Will replace harmful chlorofluorocarbons (CFCs) with environmentally
safe nitrogen. _Background:_ Nitrogen is ideal for spray cans -- it's
cheap and plentiful, it doesn't react with can contents or damage the
ozone layer. _Obstacle:_ Nitrogen must be kept in liquid form under
high pressure...and strengthening an entire can is too expensive.
_Solution:_ Liquid nitrogen kept under pressure in a small metal bulb
within the can. The bulb's valve transfers nitrogen evenly to the liquid
in the can when it is used. _Developer:_ Overseas Technology, 61A
MacQuarie St., Sydney 2000, Australia.
I've a couple of reservation about this. The first may be merely picking
a nit: I don't think you CAN liquify nitrogen at room temperature,
regardless of the pressure used. At least, I don't think it's been done.
The phase-transition weenies will KNOW rather than think what's known
about this; let them speak up. In any event, it may be possible to cram
enough nitrogen into a small metal bulb to do the job, whether or not
it's in the liquid phase.
Secondly, explosion hazard in a "hostile thermal environment". You
haven't lived until you've built a fire under an aerosol can of
automobile starting ether, but that's another story. Aerosol cans have a
bad reputation among firefighters as potential bombs: we're taught to
beware of such things. Vanilla aerosol cans could be a snap of the
fingers compared to one of these nitrogen-powered cans if overheated. I
hope they build in one _reliable_ safety valve.
Other than that, I wish 'em luck.
PS: Didja know nitrous oxide is used as a propellant in the aerosol
*** cream you get at the store? It's true!
PPS: Where I used to work, we used nitrous oxide as an oxidant for
acetylene in an atomic absorption spectrophotometer furnace (air
wouldn't get things hot enough; oxygen would melt the burner head).
Trading in an empty cylinder down at the welding supply shop one day,
one of the yardmen looked at me quizzically and asked, "What do you guys
use laughing gas for?"
I explained, and he laughed and said, "Sure, sure."
I guess he had his own ideas about it. I rather suspect some of the
students used to sneak in there and fill up a couple of balloons, but I
never caught any of 'em at it.
"...above all shadows rides the sun, and stars forever dwell...."
- J.R.R. Tolkien