It does not seem possible that the liquid remains from a burning candle can equate to the wax that once was. (esp. dripless type)
Where does it go? If some evaporates, does one find waxy build-up somewhere when it condenses? Any ideas?
I’d rather have a bottle in front of me than a frontal lobotomy - Hawkeye 4077th
Referring to Manhattan’s reference…
Can someone comfirm Cecil’s answer? This does not seem correct. The wax inhibits the flame from consuming the wick in seconds such that a candle can burn for hours.
The capillary action is hardly believable when the wick is 99% surrounded by solid wax.
I can’t see how the capillary action would have a chance to get established.
{Aside: Water and CO are always bi-products of combustion…no matter how “clean” one claims the fuel will burn.}
{Moderator may wish to move this from “General Questions” to “Comments on Cecil’s…”}
The scary thing is that 90% of the people think they’re above average! - unknown
I hope everyone will forgive my heresy, but as usual, How Stuff Works does a better job than Cecil at explaining the mysteries of our world’s physical phenomena.
~ Complacency is far more dangerous than outrage ~
My hypothesis, FWIW:
The wick in a candle is saturated with wax. Same as the wick in an oil lamp. The wax in the immediate vicinity of the flame (as well as the wax in the wick itself) is melted by the flame (remember that wax has a very low melting point), and that liquid wax is what’s burning. If you look at the top of a candle, there’s a little puddle of liquid wax right around the wick, and it’s this liquid wax that’s fueling the flame.
IIRC, wax doesn’t burn all that easily, so you need the wick to move things along. (WAG: I imagine that’s why it came into use in the first place, as a wax taper is less likely to be consumed by flames than a kerosene or oil lamp.)
Well, that’s my theory. Any takers?
*Jinx: Referring to Manhattan’s reference…
Can someone comfirm Cecil’s answer? This does not seem correct. The wax inhibits the flame from consuming the wick in seconds such that a candle can burn for hours.
The capillary action is hardly believable when the wick is 99% surrounded by solid wax.
I can’t see how the capillary action would have a chance to get established.*
Why is this unbelievable? Initially, the wick is saturated with wax. After being lit and charring the wick, the flame immediately melts wax closest to the wick and begins drawing it up by capillary action. When the flame is snuffed, enough wax is in the wick to initiate the process at the next lighting.
The wick is protected because the ignition point of the wick is higher that for wax. (This is also why you can boil water over a flame with a paper cup. The boiling water is only 212[sup]o[/sup], while the ignition point for the cup is 451[sup]o[/sup].) The drawn wax only goes a certain distance up the wick before it’s burned off. The unprotected wick then burns off.
With a oil lamp (ala Little House on the Prarie), the liquid fuel protects the wide fabric wick. But since the wick is pinched off, the flame can’t go down the wick any further. But with wax candles, the flame is allowed to burn as much wick as possible. Hence why oil lamp wicks last longer.
You’ll notice if you tilt a candle so that all the melted wax runs off the side instead of pooling that the wick begins to burn away quicker and ends up shorter. That’s because not enough wax is drawn to protect the wick, so it burns away.
{Aside: Water and CO are always bi-products of combustion…no matter how “clean” one claims the fuel will burn.}
It’s water (H[SUB]2[/SUB]0) and carbon dioxide (CO[sub]2[/sub]) (not carbon monoxide [CO]) as combustion products that define a clean burn. Unclean burns are what produce CO, sulfer oxides, and whatever else might be made from the fuel being used. Candles being mostly hydrocarbons, they don’t have many waste products other than water and carbon dioxide. (Some CO is made, as well as by-products of any perfumes in it.)
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A reply to AWB II:
Still thinking about the wax issue, but…
In studying combustion, you will find that the presence of CO as a bi-product is an indication of ineffecient burning. The more CO present, the less efficiently a flame is burning. This does factor into a “clean” burn.
There is an “ideal” equation for combustion in which CO is not a bi-product. Of course, the ideal world is hypothetical. The natural gas industry ran TV ads implying that burning natural gas does not yield CO. While gas might burn highly efficiently, CO is always a bi-product in the real world…along with others, like CO2, which I did not touch upon.
The scary thing is that 90% of the people think they’re above average! - unknown
It lands on your face and hair, and, through ciliary movement, is transported to your ear hole. Every time a candle is sold, the Q-Tip guys think, “ cha-ching !”
Everyone seems to be ignoring a key point (mentioned in the How Stuff Works link): Solid wax doesn’t burn. Neither does the liquid. What’s burning is the vapor.
The flame melts the wax. The wax wicks up the wick to the flame. The closer it gets to the flame, the hotter it gets. At a certain point, it turned to gas. That’s what’s burning.
Simple Gedanken proof: if the liquid wax were flammable, the flame would immediately spread to the puddle of liquid.
Your match is enough to melt the dried wax on the wick and turn it to liquid, then to gas.
“East is east and west is west and if you take cranberries and stew them like applesauce they taste much more like prunes than rhubarb does.” – Marx
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I think RealityChuck’s right about the vapor. I once saw the liquid wax puddle “ignite”; on closer inspection, however, I saw that the flame was dancing on the surface of the puddle, and the puddle itself wasn’t actually burning. So it must have been the vapor burning. I missed that detail in my earlier explanation.
BTW, Jinx is right about CO and CO2 (I don’t remember how to do subscripts, sorry). CO2 is the “preferred” byproduct; CO is toxic and kills you quickly, whereas CO2 is commonly found in nature anyway, and plants use it. Of course, it is also a greenhouse gas (so you might say it kills you slowly), but that discussion belongs in Great Debates.
It never ceases to amuse me how people will quibble with Cecil’s masterful, simplified so-the-complete-idiot-can-understand-it explanation of a simple mechanism like a candle flame. Or question his physics.
The Straight Dope motto should be “Casting pearls before swine since 1973.”
I assume you are referring only to the specific case of burning hydrocarbons. When hydrogen burns the exhaust is pure water, no CO or CO2. A lot of things will burn other than hydrocarbons, and their exhausts vary in relation to their original makeup, clean burn or not.
I think RealityChuck’s wax vapor suggestion has merit. The prior suggestion that the wax on the wick melts ahead of the flame and then the liquid wax burns would grant little resistance to the slow the flame from burning straight down through the core of a large, decorative candle, for example.
By the way, Woodja, could ya explain what else burns besides hydrogen and hydrocarbons?
Everything I can picture is an organic.
The scary thing is that 90% of the people think they’re above average! - unknown
The definition of burning is rapid oxidation. Purists might also require that it be exothermic. Many elements and compounds will rapidly combine with O2 in an exothermic reaction. Take magnesium (not orally): I think most of us have seen the high school science demonstration of a burning strip of pure magnesium, an element and so by definition something that does not contain other elements like carbon and hydrogen. Most other metals will burn at a high enough temperature too, and many non-organic compounds (compounds not containing carbon, by definition) and elements will also burn in the sense that they will combine with oxygen in an exothermic reaction: e.g. sulfur and many no-organic sulfur compounds, etc.
Myself, I am a big fan of thermite, a combination of iron oxide and aluminum that under the proper conditions will burn hot enough to melt stone: Fe2O3(s) + 2Al(s) --> Al2O3(s) + 2Fe(s) dH = -849 kJ/mole
The reaction will raise the thermite mass to more than 3000 *C, nealy twice the melting temp of iron (1535 *C).
flame on
Woodja, sulfur did come to mind after I posed the question. I forgot about magnesium. And, I guess for that matter, there are many salts which can burn such as those used to make fireworks (I believe “salts” is the correct term for these compounds, but correct me if I’m wrong).
Your earlier comment was correct - I am most familiar with the combustion of organics. About metals burning, like Fe, wouldn’t it melt first, maybe turn to liquid rust, before really burning?
The scary thing is that 90% of the people think they’re above average! - unknown
Sorry, don’t know off hand the kindling temp of iron. Kindling temp of thermite is 1550*C, but that’s a bit different since Fe2O3 loses O3. I guess thermite is more a case of aluminum burning, using Fe2O3 as an oxidizer. You’re right that it would need to vaporize to really burn well, but that’s true of most things (liquid hydrogen doesn’t burn, only gas). I remember in high school the chem teacher demonstrated burning metal by putting various powdered metals in a Bunsen burner flame, and noting the different characteristic colors produced as each metal oxidized. It probably needs a catalyst or oxidizing agent to really cook.
Maybe I’ll dig out the old chemistry book.
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Woodja, when you talk about “burning powdered metals”, I think you are thinking of the “salts” used in fireworks. I forget the salt compounds used in high school chem, as well.
Cupric this and ferric that…here a ferric, there a ferric, eiei-o!
The scary thing is that 90% of the people think they’re above average! - unknown
I’m just waking up to smell the sulfur, but when we speak of sulfur burning, it’s usually not in a pure state, either.
I don’t have much knowledge about metals, in their pure form, burning. Even that strip of magnesium…is it 100% pure magnesium?
<thinking Jinx might want to go to the library and get a book on basic chemistry…> 
For an interesting ‘experiment’ with candles, take a small plate, preferably with a circular ridge, making the center at least 1cm deep.
Take a short candle, either a votive, or a chopped down regular candle, and feed a lot of wax into it. One way it to take a candle, chop off the bottom few cms, and pull the wick out of the rest. Use the lit bottom piece to melt the main candle until it fills the bottom of the plate, the deeper the better.
Take a strip of paper about 1.5 times deeper than the wax, the thickness of tractor-feed strips is generally good. Take the strip and roll it up around something. A pen will work, or something a bit bigger. When you’ve got a tight roll of paper that will stick up out of the wax, push it down into the wax, open side up (and down) so you basically have a circular wick. Light it.
If you rolled the paper tighly enough, and tucked in the loose end, the paper won’t unwind and burn, you’ll get pretty well the same capillary action you do with a real wick. Not quite as strong, so feed wax in to keep the level high, when it starts to burn off.
The circular flame looks pretty neat on its own, but if you look closely, at the space in the middle, you’ll see rolling clouds of smoke, little tornadoes, etc.
And it casts lots of light, so it’s a functional candle as well.
The flame in the middle should be enough to keep the plate of wax melted. If it isn’t, and the flame is of reasonable size, the plate is too wide.
For those with a twisted sense of fun, something I discovered while doing this demo for friends… Cheesies float on wax and make good wicks. Once you’ve got a plate of liquid wax, a cheesy floating on it, lit, will keep it liquid, and similar to those boats we used to make go with little soap chips, will putter around the plate… For best results, select a cheesy with one end larger than the other.
Have fun.