Consider the Lowly Flame
Miscellaneousby Bernie Keating
• Punching up Wikipedia since 1885 •
A FLAME IS A MIXTURE of reacting and, more often, over-reacting "gases" and "solids." During this mixture or "church social," they emit visible and infrared light that create an effect that is like totally awesome on any and all Jimi Hendrix posters.
In many cases, such as the burning of organic matter, (i.e., wood, straw, rubber, heretics, your candle at both ends, and the like), or even in the case of incomplete gas combustion (pass/fail, if you don't want to take an incomplete), incandescent particles called soot produce the red-orange glow of what you people probably refer to as "fire." Then it's over the rooftops step in time!
This light has a continuous spectrum that is shown in the form of a mind-numbing slideshow usually in the spectrum's family room. So, if the slide projector comes out, by all means drop, roll, and bolt for the door.
Complete combustion of gas has a dim (or "stupid") blue color due to the emission of radiation (commonly blamed on the dog) from various electron transitions from excited molecules. What exactly excites these molecules still puzzles science folks, although it can be said with certainty it is not the slideshow going on back in the family room.
Oxygen is usually involved but it always seems to have an alibi. Hydrogen burning in chlorine also produces a flame, producing hydrogen chloride or HCl. (Oh, I’m sorry. I thought you asked.)
Other combinations producing flames are fluorine and hydrogen, hydrazine and nitrogen tetroxide, mezzanine and terrace, and, of course, over-enthusiastic Cher fans.
Oh! And there is also photon emission by de-excited atoms and molecules in the gases. Right?
The glow of a flame is as complex as a troubled teen or Van Gogh in his final days, your choice.
Much of the radiation is emitted in the visible and infrared bands, which are featured primarily on Youtube but Myspace gets its fair share.
The flame's color depends on the temperature of the radiation and the chemical makeup for the emission spectra. It just does.
The dominant color in a flame changes with temperature. A photo of a forest fire is an excellent example of this color variation. Near the ground, where all the kids are huddled together wearing matching sweaters and trying to hold still, the fire is white or yellow (who knows which?), which is the hottest color for organic material or at least this season anyway. That could all change in the fall. Above the yellow region, where the proud parents stand, drinks in hand and scolding the kids, the color changes to orange, which is cooler, then red, which is cooler still. It is not until someone starts making rabbit ears, the photo becomes the coolest ever.
Above the red region, sadly, combustion no longer occurs and the uncombusted carbon particles start to fume as the whole gang asks the carbon particles to "take one more, just for safety."
NASA (National Aeronautics and Space Andsomethingelse), of the United States, has recently found that gravity also plays a small but tasteful role (i.e., no nudity) in a flame's formation.
The common distribution of a flame under normal gravity conditions depends on convection, as soot tends to rise ruthlessly to the top of a flame stepping on anyone and everyone who tries to get in its way.
In "micro gravity" or "zero gravity" or "dude, where's my gravity," convection no longer occurs — it stops eating, stops returning calls, walks around in a old bathrobe all day, generally letting itself go.
With convection out of the picture, the flame becomes spherical with worry, with a tendency to become more blue (or "depressed") and more efficient, inexplicably feeling it should somehow pick up the slack.
However, the flame in zero gravity may go out if not moved steadily, as the CO2 tends to smother the flame mostly with questions, accusations and empty threats. So who can blame it? Consequently, when held in zero gravity, birthdays, Passover meals, and silent vigils tend to be a mess.
In combustion engines, various steps are taken to eliminate a flame. First, a stern warning, then getting written up, and as a last resort, a free ticket on the next bus out of town.