Tommy Jacoby, age 7, of North Vancouver, B. Columbia, Canada, for his question:

How do they make charcoal?

It's almost time to buy some smudgy black charcoal for outdoor summer barbeques. In olden times, a village often had a charcoal maker who worked off in the woods. He made enough for everybody, though some people liked to make their own in the backyard. Nowadays, they make our fancy charcoal chunks in special ovens. This is a better way to do it. But modern charcoal makers still use the same old recipe they used ages ago, with a few sensible changes.

Charcoal feels somewhat like black chalk and looks like sooty carbon. Actually soot and charcoal are made mostly of carbon    and there is a lot of carbon hidden in ordinary wood. You might never guess that our neat little charcoal chunks start out as ordinary wood, but they do. Ages ago, our ancestors discovered how to make charcoal by roasting sticks and chips of wood very, very slowly. And nobody has invented another way to do the job. In olden days, a village charcoal burner often lived in a clearing in the forest. There he could find enough wood and also roast it where the fumes did not pollute the air around the village. His roasting pit was a hole in the ground, packed with sticks and chips. As soon as he lighted the fire, he covered it with a pointed roof of wooden slats and topped the whole thing with shovels of dirt and grassy turf.     This was not quite enough, because fire cannot burn without air. A strong draft makes wood burn with fast flames. The charcoal burner needed a slow, slow fire, so he gave it only a little air. He made a few smallish holes near the bottom and a larger hole in the pointed roof to let the fumes escape. The fire toasted and roasted the wood for days and days. It turned some of its unwanted chemicals into gases and drove them through the roof. But the sooty black carbon in the wood stayed behind.     The roasting wood shrank and shrank and turned sooty black. When at last it was done, the charcoal burner shoveled dirt and damp ashes over his oven. This shut off the air supply and the fire went out. The oven was left to cool for several days. When it was broken apart, there was the charcoal. Nowadays, charcoal making is neater and faster. They load the wood into huge containers over a slow fire. They get about 30 pounds of charcoal from 100 pounds of wood. (The olden charcoal burner got only about 20.) We also save some of the waste gases to make useful chemicals, such as acetone and acetic acid.

We can make charcoal from roasted bones and other things that contain lots of carbon. Most of it is fine for filtering out odors and unwanted particles from air and water. Sometimes the waterworks filters out dirty debris through beds of charcoal. Sugar manufacturers may use layers of charcoal to filter their thick syrup. In some countries, they heat rooms with charcoal fires. But burning charcoal gives off suffocating fumes. When it's used indoors without a very good draft, windows must be open to let in fresh breatheable air.