Making charcoal
Growing up I knew charcoal as the square, chemical-soaked briquettes people bought in bags and poured into the barbecue grill once a summer. Like so much else in our lives it came from a store, wrapped in plastic and pre-treated for shelf life, with no sense that it shared a name with something amazingly useful, which hundreds of generations had made themselves.
Charcoal is simply wood that has been burned without oxygen, either by being heated but sealed away from oxygen or, more commonly, setting it on fire and then cutting it off from the air, keeping the wood from burning completely into ash. Most other substances in the wood are driven off, leaving a porous shape of almost pure carbon, lightweight and easy to transport.
It can purify water by soaking up impurities, as in many kitchen sink filters, and treat poison victims when crushed and drunk in a fluid. It allows people to burn fires hotter than wood, enabling people to smelt iron or shape glass in a way that wood fires cannot. It can be added to soap for abrasion, crushed to make ink or paint or mixed with minerals to make gunpowder.
Perhaps the most surprising use, one that gained a burst of attention in recent years, involves trapping carbon from the atmosphere. Frequent readers of this blog might have already heard of this and can feel free to skip ahead a few paragraphs – but for the unfamiliar, I will recap the basics.
Farmers in Brazil have long known about the “black earth,” or terra preta, found over vast areas of the Amazon. In the last decade or two archaeologists have begun to realise that the terra preta was not a naturally occurring phenomenon, but had been cultivated over centuries, if not millennia.
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