Day One

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.