The flames in my gas grill are blue, but the candles on the dinner table burn with a yellow flame. What makes flames different colors? It's a matter of how much oxygen is available to the burning fuel. Lots of oxygen makes blue flames, while a limited amount of oxygen makes yellow ones. Let's look at the yellow flame first.A candle is really a very complex flame-producing machine. First, some of the wax must melt, then the liquid wax must be carried up the wick, then it must be vaporized to a gas, and only then can it burn—react with the oxygen in the air to form carbon dioxide and water vapor. This is far from an efficient process.If the burning were 100 percent efficient, the wax would be transformed completely into invisible carbon dioxide and water. But the flame can't get all the oxygen it needs to do that just by taking it out of the air in its immediate vicinity. The air, with its flame-nourishing cargo of oxygen, just can't flow in fast enough to take care of all the melted and vaporized paraffin that is ready to burn.So, under the influence of the heat, some of the unburnable paraffin breaks down into tiny particles of carbon, among other things. These particles are heated by the flame and become luminous; they glow with a bright yellow light. And that's what makes the flame yellow. By the time the glowing carbon particles reach the top of the flame, almost all of them have found enough oxygen to burn themselves out. The same thing happens in kerosene lamps, paper fires, camp fires, forest fires, and house fires: yellow flames, all. Air just can't flow in fast enough to make the fuels burn completely to carbon dioxide and water.Gas grills and gas ranges, on the other hand, start out with a gaseous fuel—no vaporizing required. That makes it easy for the fuel to mix with lots of air, so that the burning reaction can go at full blast. Because the fuel is burning almost completely, we get a much hotter flame. And it's a clear, transparent flame because no glowing carbon particles clutter it up. Want hotter yet? Why not mix pure oxygen, instead of air, with the fuel gas? After all, air is only about 20 percent oxygen. Glassblowers use a torch that mixes oxygen with natural gas (methane), to produce a flame temperature of about 3000 degrees Fahrenheit (1600 degrees Celsius). A welder's oxyacetylene (oxygen plus acetylene gas) torch can reach about 600 degrees Fahrenheit (3300 degrees Celsius). Clear, blue flames, all—except when the torch is improperly adjusted so that the gas doesn't get enough oxygen to burn completely. Result? A yellow, sooty flame.
Selection from What Einstein Didn't Know by Robert L. Wolke. Copyright © 1997. Reprinted by permission of author.





the B's, those electrons will have to push their way through our circuit, doing work for us along the way—anything from lighting a flashlight bulb to making a little pink bunny wander vacuously around while beating on a drum.To make a battery, then, we'll make a compact little package containing lots of A atoms and B atoms. But we'll keep them separated from one another, usually with a barrier of wet paper. They won't be able to do their electron passing until such time as we complete the circuit, when we hook up the battery and close a switch that allows the electrons to flow from the A atoms through our interposed gadgetry to the B atoms.Different types of batteries are made of different kinds of A and B atoms. The most common ones are manganese, zinc, lead lithium, mercury, nickel and cadmium. In the familiar AAA (no relation to what we've called "A atoms"), AA, C, and D batteries (there once was a B battery, but it isn't used anymore), zinc and manganese atoms are the A's and B's. The zinc atoms are the electron passers and the manganese atoms are the electron receivers. The battery's voltage, in this case 1.5 volts, is a measure of the force with which zinc atoms pass their electrons to manganese atoms. Different combinations of passer and receiver atoms will make batteries with different voltages, because they have different degrees of eagerness for passing and receiving electrons.When all the passer atoms have passed their quota of electrons to the receivers, the battery is dead, and, alas, the bunny stops here.Nicad (nickel-cadmium) batteries, as well as your automobile's lead-acid battery, are rechargeable, however: we can reverse the electron-passing process by pumping electrons back from the receivers to the passers, and then the passing game can begin all over again. Unfortunately, though, every time the battery is recharged, some mechanical damage is done to its innards, and even a rechargeable battery won't last forever.
Selection from What Einstein Didn't Know by Robert L. Wolke. Copyright © 1997. Reprinted by permission of author.




the B's, those electrons will have to push their way through our circuit, doing work for us along the way—anything from lighting a flashlight bulb to making a little pink bunny wander vacuously around while beating on a drum.To make a battery, then, we'll make a compact little package containing lots of A atoms and B atoms. But we'll keep them separated from one another, usually with a barrier of wet paper. They won't be able to do their electron passing until such time as we complete the circuit, when we hook up the battery and close a switch that allows the electrons to flow from the A atoms through our interposed gadgetry to the B atoms.Different types of batteries are made of different kinds of A and B atoms. The most common ones are manganese, zinc, lead lithium, mercury, nickel and cadmium. In the familiar AAA (no relation to what we've called "A atoms"), AA, C, and D batteries (there once was a B battery, but it isn't used anymore), zinc and manganese atoms are the A's and B's. The zinc atoms are the electron passers and the manganese atoms are the electron receivers. The battery's voltage, in this case 1.5 volts, is a measure of the force with which zinc atoms pass their electrons to manganese atoms. Different combinations of passer and receiver atoms will make batteries with different voltages, because they have different degrees of eagerness for passing and receiving electrons.When all the passer atoms have passed their quota of electrons to the receivers, the battery is dead, and, alas, the bunny stops here.Nicad (nickel-cadmium) batteries, as well as your automobile's lead-acid battery, are rechargeable, however: we can reverse the electron-passing process by pumping electrons back from the receivers to the passers, and then the passing game can begin all over again. Unfortunately, though, every time the battery is recharged, some mechanical damage is done to its innards, and even a rechargeable battery won't last forever.
Selection from What Einstein Didn't Know by Robert L. Wolke. Copyright © 1997. Reprinted by permission of author.