I have a couple of things that someone may want to look at.
First the URL is not hyperlinked as they normally are.
Second (and most important) I would suggest changing your definition…
Fire is the rapid combination of oxygen with fuel in the presence of heat, typically characterized by a visible flame, a body of incandescent gas that contains and sustains the reaction and emits light and heat.
This would keep the definition from being negated by the following statement.
Flame isn’t just the result of fire; it is the fire.
Otherwise you are saying that fire doesn’t require a flame… but flame is fire…
I suspect you might have stumbled across the column right as it was being put up on the site, EEMan. Anyway, the URL is linked to now, the column is: What exactly is fire? (22-Nov-2002).
Anyway, I think I see your point: Cecil defines fire as being “typically characterized by flame,” which of course implies that there are atypical fires not characterized by flame. At the same time, he states that “flame isn’t just the result of fire; it is the fire.” So can you have a flameless fire, or not?
However, I think that Cecil has already incorporated your suggestion by including the word “incandescent” into his definition of flame. Admittedly, this is a little more awkward phrasing (is flame necessarily incandescent, or not?), but I think we can safely blame the editing of Ed Zotti for that.
Thank you for your fast response… though I am not sure that incandescent covers it… the reason I say this is, they are describing the ‘flame’ as being incandescent. So if the fire is ‘flameless’ the fire is then also ‘dark’ (non-light emitting)… I can this would be a ‘black box (body)’ energy source or the like… but not really a ‘fire’ as I come to think of them.
This is possibly the best explanation of a fire I have ever heard, and Cecil’s continued explanation that he believes all fires have flames, takes care of the definition’s inconsistencies. Though in order to make the definition as clear as possible, I think visible should still be added (or the word typically needs to be removed).
Good column, and a very basic question often overlooked. I’d just like to add two things:
1.) If you want to learn more about flame, get thee a copy of Michael Faraday’s Chemical History of a Candle. Sounds boring as hell, but it isn’t. Faraday was a legendary scientist, and he used to give a popular series of lectures at Christmas time (a tradition that has been revived at several museums), accompanied by a lot of very clever demonstration experiments. This book is basically a transcript of the lecture, with pix of the experments. Collier’s reprinted it in paperback. Well worth tracking down.
2.) The visible part of the flame – the yellow glowing stuff – is essentially carbon (soot) heated by the burning gases and glowing by the blackbody radiation it’s giving off.
Isn’t a combustion reaction by definition one involving oxygen? If so then if a ‘fire’ is a ‘combustion’ then it requires oxygen… I have never seen wood in a fluorine atmosphere… so I have never seen this type of fire… but if you pass electrical current through flourine then you get a ‘cold glow’ that isn’t fire… (flouresence from the release of photons from the flourine)…
CalMeacham…
You stated
The visible part of the flame – the yellow glowing stuff – is essentially carbon (soot) heated by the
burning gases and glowing by the blackbody radiation it’s giving off.
Then why would the candle’s flame change color in space (ie blue spheres verses yellow tapers…
As far as I know, oxidation doesn’t require oxygen. If you put any substance that is able to be oxidized into a flourine atmosphere and apply heat, you’ll get rapid oxidation. I imagine that a chunk of sodium in a pure flourine environment would fit everyone’s idea of what a fire is.
Perhaps someone who recalls their college chemistry classes better than I do can confirm this.
I believe that’s due to different flame temperature. The absence of gravity means that heat no longer rises, which would cause two different effects that I can think of: 1. since air is not drawn past the flame the rate of heat lost to convection is greatly reduced; 2. likewise, fresh oxygen is not brought to the flame as quickly, so it doesn’t burn as fast. I suspect the lower heat transfer rate dominates, giving the hotter blue flame.
Brave Sir Robin: But oxidation by definition requires oxygen. Oxidize: To combine with oxygen.
There is one significant inaccuracy in your response about the nature of fire. Open wheel auto racing, the Indy Racing League (IRL) and CART in the US, use methanol in their cars. This results in no visible flame (occasionally a very faint blue flame can be seen) which is quenched by diluting the methanol with water. NASCAR, on the other hand, runs on good old-fashoned gasoline (Union 76, I believe) which produces a very bright yellow flame after a crash (usually at least one per race) which is quenched by fire extinguishers.
It’s been a while since College Chemistry… but I don’t think ‘heat rising’ actually has anything to do with heat… it has to do with the gas density… thus the less dense air move up through desner air…(sand moving to the bottom of a pond…)… is your result then based on the contention that the relative movement of different density substances is due to gravity?
I also seem to recall that different chemicals burn different colors, this might be do the different ‘temperatures’ they burn at…but I don’t know why the rate at which air pressure equilizes would have anything to do with gravity (as opposed to the pressure of the gas inside the container).
Hum… going to have to do some expirements when I get home…
Yes. You’re right, though: my phrase “heat rising” is pretty sloppy. Rather, hotter air is less dense, and less dense air will rise (or more dense air will fall, if you prefer). And this effect is absolutely due to gravity. Consider: how would denser air, or sand, or a spanner wrench, fall, if there’s no “down” to fall toward?
? If this was in response to my previous post, then that idea is not what I meant. The air around a flame heats up; with gravity, the warmer air will float upward, and be replaced by cooler air. The cooler air has more oxygen. Without gravity, the (warmer) air around the flame tends to stay in place, which means that the flame is surrounded by air in which the oxygen is already depleted. No air pressure effect at all.
Here was my thoughts on this (and I am by no means claiming to know the answer), unlike solids or liquids that may require gravity to seperate the different density items, gas has a ‘pressure’ associated with it. So a less ‘dense’ area would then be one of ‘lower pressure’, and I don’t see how gravity would effect this. So the candle would heat up the air, then the air pressure would drop, the ‘colder’ more ‘dense’ air would then rush in to fill the ‘parital vacuum’. Much like opening the shuttle door to space… you get ‘explosive’ decompression reguardless of gravity (though this would not be nearly as violent). The warmer air would then circulate with the cooler air… causing an outward movement of the heat. The only thing that I can see being different then here on terra firma, is the heat would not ‘rise’ but rather ‘expand’.
If the flame is composed of pure substances, then you could expect a sort of Zeeman shift (due to the magnetic field) in the absorption spectrum. There is an example: when sodium is present in the flame, a magnetic field will change the flame’s shadow due to a sodium lamp from essentially dark to much brighter (a magnetic field disrupts resonance with the incoming light).
But then again, how many people is this going to affect?
Actually quite the opposite. For an ideal gas (air being close enough), pressure, temperature, and volume are related through the ideal gas law: PV = nRT, where n and R are constants. Put another way, for any given mass of air, P[sub]1[/sub]V[sub]1[/sub]/T[sub]1[/sub] = P[sub]2[/sub]V[sub]2[/sub]/T[sub]2[/sub]. This means (to digress a moment for the sake of an example) that if you pumped air into a sealed chamber (constant volume) and heated it up, the pressure would increase, since the quantity PV/T must be the same at all times.
Suppose now you had a small mass of air in your house. You heat the small mass of air (with a candle, say) We can say, with reasonable accuracy, that the pressure everywhere in your house is the same. The heated air will not increase or decrease in pressure, because the pressure will stay equal to the pressure in the rest of the house. Since the quantity PV/T must be the same at all times, and the pressure is constant, the volume must increase when the temperature increases. If the same mass of air increases in volume, it is by definition less dense. In your house, in a gravitional field, the less dense air rises. On the space shuttle, it just stays where it is.
Also, fire may not be effected by magnetism but can produce highly ionized smoke. making the smoke produced from a fire to be very conductive. We have had many cases where a fire has broken out underneath a power line and had the smoke provide a flashover path to ground, and that was thirty to fourty feet or more.
According to this NASA site, “fire is plasma”: http://science.nasa.gov/newhome/headlines/ast07sep99_1.htm and therefore conducts electricity and is affected by magnetic fields. Cecil’s explanation is better than the dictionary, but doesn’t seem quite to jibe with the explanations of plasma around. Flame seems closer to the fusion reactions in the sun than NASCAR racers. Perhaps an explanation of fire is better expressed as “plasma generated by the combustion of a fuel with oxygen in the presence of heat”.
PV=nRT is Pressure * Volume = Number of molecules * a constant R* temperature
So pumping air into the system you can’t say that n remains constant… but for example… lets just solve a simple equation…
PV/nRT = 1
now lets say all the numbers are equal to unity (ie 1) so you have
11/ 11*1 = 1 everything works out…
now… lets just double the Temperature… and leave everything physical constant (everything but pressure)
P1/ 11*2 = 1
cross multiply…
2 = P
so indeed the pressure is doubled… so your example works… for a constant area…
but were not talking Ideal Gas Behaivior… this is where my confusion comes in to why gravity makes any difference…
were talking about ‘micro-currents’ and ‘gas eddies’ so even though we are talking one container… we are trying to see what happens in that container… (bear with me I’m an EE not a ME) this would be fluid dynamics…
I don’t see how the response of the excited atoms could be held in a single spot… in fact without gravity to hold them down… i would assume the would move MORE not LESS…
Time to go talk to a co-worker… and break out the calculator…
Zut, Dictionary.comhttp://dictionary.reference.com/search?q=oxidation gives the additional definition “A reaction in which the atoms in an element lose electrons and the valence of the element is correspondingly increased.” Also please note definition 3 from Merriam Webster, which does not indicate that oxygen is required.
Oxygen is certainly the most common oxidizer, but it isn’t the only one. Flourine is going to be rather effective at ripping electrons away from just about anything.
Huh? Plasma is a collection of ionized particles, circulating in a gas-like state. Flame is rapidly combusting gases with glowing red-hot (not ionized) carbon particles in it. Ain’t no similarity.