Well, my challenge this time is to make a carbon dioxide
filter. For this I need some limestone. Heating limestone
(calcium carbonate) at a high enough temperature drives
off a gas called carbon dioxide, forming lime. When
this is added to water it gives calcium hydroxide –
a solution called limewater. When air that contains
carbon dioxide is bubbled through limewater, the carbon
dioxide is removed – it reacts with the calcium
hydroxide to give calcium carbonate again.
Sounds easy enough, but the particular type of limestone
round here needs a really high temperature to drive
off the carbon dioxide. All I have is a small stove
that I know will not give me the kind of high temperatures
I need. Sure, there’ll be some lime formed, but
enough for my purposes? Maybe – maybe not. I've
little choice but to suck it and see.
The first batch of local limestone I try is hopeless.
Hardly any conversion to lime at all. It takes several
more trips out from the mine to find the right kind
of limestone that will, at sufficiently low temperatures,
give me the lime I need.