How Do Trick Candles Work?

Today is my birthday. While you're surfing mentalfloss.com, I'm home celebrating with single-malt scotch and Rock Band. Wish you were here. In honor of my special day, here's the science behind the trick in trick candles, which I really hope aren't part of today's festivities, for they are cruel and unusual and prolong the wait for delicious cake.

A lit candle wick melts the paraffin wax near it, absorbs the liquid wax, and pulls it upward. The flame vaporizes the wax, the vapor burns and keeps the flame lit, allowing the cycle to continue. When you blow out a regular candle, you might notice the little wisp of smoke that rises from the wick. That's a last little bit of paraffin that's been vaporized by the dying ember of the wick, but didn't ignite because the ember isn't hot enough.

The trick to a re-lighting candle, then, is getting enough heat going to ignite the escaping vapor and bring the flame back to life. The folks who don't want you to eat your cake and make these candles usually turn to magnesium for the job. Magnesium, the ninth most abundant element in the universe by mass, is an alkaline earth metal that's highly flammable and ignites at temperatures as low as 800 degrees F (430 degrees C) when powdered or shaved into thin strips. Powered magnesium is put inside the wick, where it's kept cool and shielded from oxygen by the liquid wax. When the candle is blown out, the wick's ember ignites the magnesium "“ if you watch closely, you can see little bits of magnesium sparking "“ which ignites the paraffin vapor and re-lights the candle. Magic!

The problem, of course, is getting the candles out once and for all when you get tired of games and want to eat (or if the cake bursts into flames). Trick candles need to be snuffed or dunked in a liquid to cut off the oxygen supply so the flame can't re-ignite. And no, you cannot use my scotch.

This question was suggested by my friend Paul. If you've got a burning question that you'd like to see answered here, shoot me an email at flossymatt (at) gmail.com. Twitter users can also make nice with me and ask me questions there. Be sure to give me your name and location (and a link, if you want) so I can give you a little shout out.

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Feeling Down? Lifting Weights Can Lift Your Mood, Too
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There’s plenty of research that suggests that exercise can be an effective treatment for depression. In some cases of depression, in fact—particularly less-severe ones—scientists have found that exercise can be as effective as antidepressants, which don’t work for everyone and can come with some annoying side effects. Previous studies have largely concentrated on aerobic exercise, like running, but new research shows that weight lifting can be a useful depression treatment, too.

The study in JAMA Psychiatry, led by sports scientists at the University of Limerick in Ireland, examined the results of 33 previous clinical trials that analyzed a total of 1877 participants. It found that resistance training—lifting weights, using resistance bands, doing push ups, and any other exercises targeted at strengthening muscles rather than increasing heart rate—significantly reduced symptoms of depression.

This held true regardless of how healthy people were overall, how much of the exercises they were assigned to do, or how much stronger they got as a result. While the effect wasn’t as strong in blinded trials—where the assessors don’t know who is in the control group and who isn’t, as is the case in higher-quality studies—it was still notable. According to first author Brett Gordon, these trials showed a medium effect, while others showed a large effect, but both were statistically significant.

The studies in the paper all looked at the effects of these training regimes on people with mild to moderate depression, and the results might not translate to people with severe depression. Unfortunately, many of the studies analyzed didn’t include information on whether or not the patients were taking antidepressants, so the researchers weren’t able to determine what role medications might play in this. However, Gordon tells Mental Floss in an email that “the available evidence supports that [resistance training] may be an effective alternative and/or adjuvant therapy for depressive symptoms that could be prescribed on its own and/or in conjunction with other depression treatments,” like therapy or medication.

There haven’t been a lot of studies yet comparing whether aerobic exercise or resistance training might be better at alleviating depressive symptoms, and future research might tackle that question. Even if one does turn out to be better than the other, though, it seems that just getting to the gym can make a big difference.

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