On Sep 15, 9:46*am, dgk wrote:
I have one of those $25 air horns - this kind of thing:

http://www.nycewheels.com/air-zound-horn.html

It is very useful for commuting, capable of easily penetrating the
headphones of joggers and such. However, I never used it in winter
before because it was too much to take off the bike when parking
outside at the office. Various lights, batteries, etc.

Now I will be able to bring the new bike into the building. So, while
I could continue to use it, I'm concerned about the effect of cold on
the bottle and its contents (air). Surely it not last as long, but
will the bottle get brittle and explode? I think it is best to not
find out the hard way.

I suppose that there's an off chance that a sharp blow would
shatter the bottle when fully inflated, maybe slightly more likely
in the cold, but I'd wager that they've thought this through and
are using a plastic that's somewhat less affected by temperature.
I pretty regularly keep plastic bottles of tonic water which have
been abused in the 'fridge without suffering explosions.

As to the PV=RT question: if you're pumping the chamber up
out-of-doors (as it is so quaintly put) when the example temp
is -15F to a mild 120psi, and then bringing the bicycle in, air-
horn undischarged, to a 78F building, you'll see a rise to
445:538::120:x or about 145psi.