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Fire is not a substance.
Just because fire HAS substance doesn't mean it IS a substance.
Fire - the light and heat and especially the flame produced by burning
To expand on the comment from lightarrow: In common usage,A flame is made of glowing gasA fire is composed of flame(s) (chiralSPO gives some more extreme examples that might be more at home in rocket science than on your birthday cake!)
Fire is the rapid oxidation of a material in the exothermic chemical process of combustion, releasing heat, light, and various reaction products.
The flame is the visible portion of the fire. If hot enough, the gases may become ionized to produce plasma.
The OP doesn't specify any meaning of "fire", ..
The OP doesn't specify any meaning of "fire", and dictionary definitions are made by lexicographers rather than scientists, so many of their definitions are faulty and they should never be regarded as the final word on anything. I'm not sure that a fire is any different from a storm if you want to call it a substance. You can have a gas or plasma without fire, light emission without fire (glowsticks), glowing gas that isn't a flame (aurora), burning without flames (sun + magnifying glass + paper --> burned holes and smoke but often without flames), and chemical reactions that release heat without fire (as in our muscle cells). Fire is a process, but it can be referred to as a thing. A storm is a process too, but again it can be referred to as a thing (the storm hit us), and this is because any process can be referred to as a thing. Calling a storm a substance would be stretching things a bit too far though, and calling a fire a substance would be going too far too - it isn't a substance, even though substances are involved in it. The ancients thought it was a substance, of course (earth, air, fire and water), so there is a long tradition in calling it such, but science has moved on.
Quote from: David CooperThe OP doesn't specify any meaning of "fire", ..When he said "Is fire a gas or not?" he clearly has the flame in mind rather than a chemical process. Teaching isn't always about taking what someone says literally but determining what they're trying to learn and in this case it's clear to me (although I understand not to you) that he has the flame in mind. That's always what I have in mind when I think of fire.
Quote from: chiralSPOJust because fire HAS substance doesn't mean it IS a substance. In this case it is because fire is a thing (as much as a gas is a thing) whereas a storm is a state of nature and not the material of nature. Not so with fire. What I said holds in this case since my analogy was about things and not a state of being.Please consider what I said and keep it in mind before you give an analogy like those above which don't apply. I.e. please look these things up in the dictionary and learn what the OP and others mean when they use a term such as this. I.e. in this case you were using a different definition of fire than the OP and I were. You were using the definition of fire as an oxidation process and I was using it as followshttp://www.merriam-webster.com/dictionary/fireQuoteFire - the light and heat and especially the flame produced by burning
If you can't see that a fire is more like a storm than a gas, you have some pondering to do! 
Of the various uses of the word as a noun, the Oxford English Dictionary offers just one that could be misconstrued as a gas: "A process in which substances combine chemically with oxygen from the air and typically give out bright light, heat, and smoke; combustion or burning:"i.e. a process involving substances, not a substance. Like cookery.
Fire - the light and heat and especially the flame produced by burning.
I posted the dictionary quotes for you to read.
I wonder if the holographic principle has anything to say about flames. As for string theory how to spin networks fit in this case?
When he said "Is fire a gas or not?" he......
You're right Pete, people should pay close attention to the OP. [8D]
"Full Definition of PHOTON1: a unit of intensity of light at the retina equal to the illumination received per square millimeter of a pupillary area from a surface having a brightness of one candle per square meter2: a quantum of electromagnetic radiation"I think the second definition is apt, but I'm not sure how I would argue with someone who claimed that the first was a better definition of photon.
Someone commented earlier on some flames being a plasma, which leads me to wonder if any flames don't involve a plasma. A tiny candle designed for a birthday cake which plays a certain tune when it's lit depends on there being plasma in the flame to complete a circuit (there being two metal strips in the wick). I've heard that there are some gases which burn with flames of sufficiently low temperature that you can hold your finger in them without injury (and which presumably wouldn't be able to set fire to a piece of paper), but do they involve plasma? A simple way to test would be to see if they can conduct electricity.
Some flames are hot enough to have ionized gaseous components of sufficient density to be considered plasma.
I am thinking of a "sparkler" that more adventurous people sometimes use on birthday cakes.This device heats up tiny pieces of metal until they reach ignition temperature, upon which they combine with oxygen in the atmosphere, releasing energy which keeps the metal hot enough to keep reacting with oxygen (until the metal burns away to nothing).Since iron oxide has a melting point of 1566C and a boiling point of 1987C, I am wondering if the reactants get hot enough to form a vapor phase of iron or iron oxide?Or does the thinly divided powder have enough surface area to allow easy access by oxygen, and the extremely exothermic reaction keeps the reactants hot?With a solid wax candle, you have to heat the organic wax to a liquid which can flow up the wick (wax melts around 50C) and then evaporates out of the wick as a vapor (boiling point around 350-400C). This presumably breaks some bonds before the oxygen can react with the wax vapor.I assume the same effects would occur for sparks from an angle grinder? So is a spark a fire? And is it a gas?
So is a spark a fire? And is it a gas?
The flame moves away from a gravitational source but does a spark?
small grey/blackish balls of some sort of burned out material
Quote from: jeffreyHThe flame moves away from a gravitational source but does a spark?A flame rises because the hot gas is less dense than the surrounding cool air, and the "lowest energy state" is with the denser air closer to the center of the Earth.A spark is a glowing piece of iron or magnesium, which is more dense than cool air, so I expect that a spark will fall in a parabola towards the ground (if it doesn't burn out first).Quote from: PmbPhysmall grey/blackish balls of some sort of burned out materialCandle wax is a hydrocarbon, whose products of combustion are CO2 and water vapor (plus a bit of carbon soot, carried away by convection)Wood has a more complex composition; in addition to the volatile products produced by a candle, it leaves behind a small amount of ash, consisting of non-volatile compounds of Potassium, Sodium, Copper, etc. But it is undoubtedly a "fire".A Sparkler produces a variety of gaseous compounds, but the spark remnants are non-volatile compounds of iron or magnesium. Does the large amount of "ash" disqualify a spark from being a fire?
If we were to apply a force throughout this container such that any gas density variations were evened out would the flame then become spherical or would it still move upwards?
I've seen it defined as 'burning' Chiral? Maybe oxidation would be more to the point though?
oxidation processes that don't involve combustion, burning or fire: ... rusting ships, etc
Quote from: yor_on on 19/12/2014 20:25:59I've seen it defined as 'burning' Chiral? Maybe oxidation would be more to the point though?I am hard pressed to think of a reaction that could qualify as burning without involving redox, but that doesn't mean it's impossible. I can think of a few cases of "explosive polymerization" (involving ethylene oxide or acetylene or similar compounds) which could potentially release enough energy to reach incandescence without involving any redox processes, and also perhaps exothermic decomposition of ozone, but these are special cases...
Yes this reaction is quite impressive. I'm not entirely convinced that the surrounding air didn't contribute to the effect,
but the reaction between Pd and Al is apparently exothermic enough on its own, that it probably would have "burnt." This isn't really a redox neutral process, though. Pd is electronegative enough that it could well have oxidized the aluminum (maybe not quite so far as to produce an ionic compound, but the bonding character between aluminum and noble metals is not entirely metallic either--I know gold and aluminum will react to form white or purple compounds that are very poor conductors, which is why Au-Al contacts are typically avoided in circuits.)