In message , Java Jive
writes
Just in case anybody's actually interested and wants to know ...

On Tue, 01 Sep 2009 00:03:38 +0100, Java Jive
wrote:

My stepfather used to teach me science through, say, explaining why
popcorn popped.

EXPLAIN

Popcorn before cooking is a seed, but the thing that makes it a little
different is that the skin of the seed is virtually impermeable.

To cook it, you place a small amount of oil or fat in a saucepan, just
enough to almost cover the bottom (so that it will, just, cover the
bottom when heated) and enough popcorn to just cover the bottom of the
pan. You then cover it with the saucepan lid (vital!), and put it
over the heat. Within a minute or two, the pan starts to tremble and
roar as all the popcorn pops. Once this is truly over, remove from
the heat and pour the popcorn into something like a colander. Serve
with sea-salt.

So, that's how you cook it, but why does it pop? The seed contains
small amounts of water vapour, which on heating turns to steam,
cooking the 'flour', or whatever you want to call the contents of the
seed, and, building up pressure until it ruptures the seed casing and
turns it inside out, all in a moment.

A favourite trick was to get an old-fashioned tin with a replacable
lid, like a syrup or treacle tin, and punch one hole with a nail
through each of the base and the lid. You then:
1) Remove the lid
2) Seal the hole in the base of the tin with a finger
3) Turn it upside down
4) Fill it with gas from the cooker (gas is lighter than air, so it
goes up into the tin). Er, turn the gas off once you smell gas! That
means it's full!
5) Replace the lid
6) Seal the hole in the lid with another finger (so you're now
sealing both)
7) Turn it the right way up
8) Run out into the garden and place it on something like a brick
9) Light the gas at the lid hole, and stand well back.
After a few seconds the lid goes about 15 feet in the air.

EXPLAIN

The thing here is that gas and air, strictly the oxygen in the air,
are only explosive if mixed in the right quantities, and what exactly
are the 'right quantities' depends on the chemical formula of the gas
used.

When you initially light the flame, it just burns like any gas
cigarette lighter, or like a gas cooker flame, only rather more weakly
because it isn't under pressure and doesn't have an optimised burner
outlet. As the gas is burned from the hole in the lid above, it is
replaced by air coming through the hole in the base below, until, when
the right quantities are reached ... BOOM!

No ****, sherlock - as they say

So what, without looking it up, it the explosive concentration for mains
gas ?

No peeking, if you don't know, take a guess ...

--
geoff