Q A friend of mine told me that wet firewood burns faster than dry wood. Is this true, and, if it is, how is it possible?
-Senia S., age 13
A Drier wood burns faster, but sometimes wetter is better. Even if a log or branch doesn’t feel damp, it still contains water in its sap. “A piece of very young pine-all sapwood-can be 40 percent wood and 60 percent water,” John Walker* told me. When you burn moist wood like that, some of the heat from the fire gets used up in turning the water into steam. That makes the wood burn more slowly, and it also leaves less heat to warm your living room or toast your marshmallows.
So does very dry wood, like the kind used for furniture, make a better fire? Not necessarily. As wood burns, John Gulland** explained, it releases gases and tiny specks of carbon into the air. To give the most heat, a fire has to burn them, too. The faster wood burns, the more gases and carbon it gives off. Very dry wood burns so fast that much of this secondary fuel escapes up the chimney or stovepipe before it has time to burn. (It’s called “smoke.”) So it’s better to burn wood that contains a little moisture-about 20 percent for wood-burning stoves. That’s why, after cutting wood, most people let it dry out for a few months before burning it.
Q Why do fingernails curve when they get longer?
-Julie B., age 12
A Our answer takes us to the nail-matrix domain-that’s the area that produces the cells that become our nails. If you take a look at your nails you’ll see a white crescent peeking up from the cuticle. That’s the visible portion of the nail-matrix domain. The rest is below the surface or hidden by skin
So why do nails curve? I asked Cindy Loomis,* who studies nail development in embryos. Cindy told me the generally accepted explanation, even though she’s not sure she buys it. So she’s working on figuring out the truth-and I’m biting my nails waiting to find out what she discovers. In the meantime (drumroll, please), here is what she has to say about the nail-curving question:
“In essence the downward curvature develops because the deep cells are produced more slowly than the cells near the surface.”
She adds: “I personally do not think this is the whole story.”
* John Walker is a forestry professor at the University of Canterbury in Christchurch, New Zealand.
** John Gulland is a wood-heating consultant for the Canadian government. You can find links to their Web pages at www.musefanpage.com.
* Cindy Loomis is an assistant professor of dermatology at New York University.
Copyright Carus Publishing Company May/Jun 2004
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