For this experience, it is more convenient to rent a table lamp. One of its wires disconnect from the plug and extend, not forgetting the good insulation.
Take a small narrow glass tube with a thin wall (easiest way is to use a glass rastegari with attenuated ends). Insert the tube with the two ends of the electrode - wiring with a diameter of about 1 mm ; secure them in the tube with electrical tape. The electrodes must not touch, the distance between them 1-2 mm.
An elongated wire from the lamp attach to one of the electrodes and the other electrode connect the wire with the free socket of the plug and isolate. You'll have the circuit open in the same area between the electrodes. Attach the glass tube in a horizontal position. It's very simple to do, if hard wire with plastic insulation: pinch the wire, and the tube will be kept. Prepare to experience complete, you can enable the plug into the network. The lamp, of course, will not burn.
Bring to the tube into which is inserted the electrodes, a lighted match. If the tube is not refractory glass, the glass will soften and tube when this little SAG. And immediately turns the lamp, despite the fact that the circuit remains open. The fact that salt included in the composition of the glass, when heated, ionized, and the glass becomes a conductor.
If the experience is not obtained due to the fact that the tube is wide, instead matches take the candle or spirit lamp. To light a candle is also a spectacular experience.
And it can be lit using molten nitrate. Attach the upright tube, the bottom of which poured a little potassium or sodium nitrate (nitrate of potassium or sodium), and put two copper wires. To the copper electrodes are not in contact, let them pass through the tube. Connect to the electrodes of the lamp as well as previous experience. When you turn on the current, the lamp, of course, will not light: solid nitrate current does not.
Heat nitrate to melting with the dry fuel tablets - lamp will flash. Ions constituting the crystal lattice of salt, gain mobility, and the circuit is closed. The lamp will be lit after you remove the flame: melt nitrate high electrical resistance, and the heat that is released during the passage of current, supports nitrate in the molten state.
This way you can put the experience not melt and from solution, for example, sodium chloride. The electrodes in this case it is better to take the graphite. Soak them first, just in a jar with water, and then in small portions, add salt, and the bulb will burn brighter.
By the way, this is a convenient method to check the conductivity of solutions. Check, for example, as conductors solutions of soda, sugar and acetic acid of different concentrations.
And another, not a normal experience with an electric light bulb, but not great, and from a pocket lantern. Tie it to the strip of sheet metal, bent at right angle, and insert the strip into small chemical glass so that the glass bulb lights were inside the Cup and was converted to its bottom. Connect the bulb to the battery: the tab on the cap, the most extreme part of the connect to the negative pole, and a strip of tin - positive. Note: solder the conductors cannot, because during the experience, the solder may melt. Need to invent a mechanical contact or use the cartridge from the old pocket lantern.
Before the start of the experiment, remove the lamp from the beaker and pour into it the sodium nitrate (nitrate of potassium in this case, it is not necessary; why will become clear later). Place the glass on asbestos mesh or metal plate and heat it in the flame of a gas burner or spirit lamp; dry alcohol is not very convenient, because it is difficult to adjust the temperature of the melt. Nitrate melts at 309°C. at 390°C is decomposed; in this interval and will have to maintain the temperature. For this change either the size of the flame, or the distance to the Cup. Make sure that the melt does not froze, even with the surface.
In molten nitrate carefully lower the light bulb. A large part of the glass cylinder must be immersed in the melt, but make sure that the upper part of the cap, to which is soldered to the conductor does not come into contact with nitrate - short circuit occurs. Lit light bulb soak in the nitrate for about an hour, then disconnect the power, turn off the burner and carefully take the light bulb. When it has cooled, rinse it with water, and you will see that the bulb inside is covered with a reflecting layer!
We have already said that when heated, charged particles in the glass acquire mobility (and therefore lit the lamp, when the tube was heated with a match). The main characters are sodium ions: already at temperatures above 300°C, they become quite mobile. The glass itself is quite solid.
When you loaded the included bulb into the nitrate melt, the glass from which the spray, was in an electric field: the spiral is a negative pole, the melt, which is in contact with a strip of tin - positive. Mobile sodium ions began to move in the glass in the side of the cathode, i.e. in the direction of the spiral. In other words, they moved to the inner wall of the cylinder.
Therefore, the mirror plaque inside sodium? Yes. But how ions are turned into metal?
Molten metals (including those made from spiral) emit electrons. From the spiral they are trapped on the inner surface of the glass and met there with sodium ions. The so-formed metallic sodium.
But why experience is not suitable potassium nitrate? Because nitrate does not seem to be involved in the process... No, participates. When the sodium ion has become a neutral atom, the glass remained negatively charged ion hole. Here and need sodium nitrate: from its melt under the action of the electric field in the glass sodium ions penetrate and fill the holes. And potassium ions is approximately one and a half times more sodium ions, they will not be able to enter the glass. In potassium nitrate lamp will simply crack.
This unusual electrolysis through the glass sometimes used in practice to obtain a layer of very pure sodium, or, more strictly, spectral clean.