And one more, not quite usual experience with a light bulb, but not from a big one, but from a flashlight. Strengthen it in a strip of tin bent at a
right angle, and insert the strip into a small beaker so that the glass balloon of the bulb is inside the glass and faces the bottom of the bulb.
Connect the light bulb to the battery: connect the protrusion on the base, connect the most extreme part of it to the negative pole, and the tin strip
to the positive pole. Please note: you cannot solder the conductors, because during the experiment the solder may melt. You need to come up with a
mechanical contact or use a cartridge from an old flashlight.
Before starting the experiment, remove the lamp from the glass and pour sodium nitrate into it (potassium nitrate is not suitable in this case; this
will be clarified later). Put the glass on the asbestos mesh or metal plate and heat it on the flame of a gas burner or spirit lamp; dry alcohol is
not very convenient, as it is difficult to regulate the temperature of the melt. Saltpeter melts at 309 ° С, and at 390 ° С it decomposes; here in
this interval and have to maintain the temperature. To do this, change either the size of the flame or the distance to the glass. Make sure that the
melt does not freeze, even from the surface.
Carefully lower the light bulb into the molten saltpeter. Most of the glass bottle must be immersed in the melt, but make sure that the upper part of
the base, to which the conductor is soldered, does not come into contact with the saltpeter, there will be a short circuit. Hold the lit bulb in nitre
for about an hour, then turn off the current, turn off the burner and carefully deliver the bulb. When it cools down, rinse it with water and you will
see that the bulb is covered with a mirror layer from the inside!
We have already said that when heated, charged particles in glass acquire mobility (therefore, the lamp was lit when the tube was heated with a
match). The main actors are sodium ions: already at temperatures above 300 ° C, they become quite mobile. The glass itself remains completely solid.
When you loaded the included light bulb into the melt of nitre, the glass from which the balloon was made turned out to be in an electric field: the
coil is a negative pole, the melt that comes in contact with a strip of tin is positive. The mobile sodium ions began to move in the glass toward the
cathode, i.e. toward the spiral. In other words, they moved to the inner wall of the balloon.
So, mirror coating from inside is sodium? Yes. But how did the ions turn into metal?
The heated metals (including those from which the spiral is made) emit electrons. From the spiral, they hit the inner surface of the glass and
connected there with sodium ions. This formed metallic sodium.
But why is potassium nitrate not suitable for the experience? After all, nitrate does not seem to be involved in the process ... No, it does. When the
sodium ion became a neutral atom, a negatively charged ion hole remained in the glass. Here we need sodium nitrate: from its melt, under the action of
an electric field, sodium ions penetrate into the glass and fill the holes. And potassium ions are about one and a half times more sodium ions, they
will not be able to enter the glass. In potassium nitrate lamp just crack.
Such unusual electrolysis through glass is sometimes used in practice to obtain a layer of very pure sodium, or, more strictly, spectrally pure.
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I wasn't putting this method forward as a way
to collect a significant amount of sodium, but just as a mere curiosity. Your second experiment sounds very interesting. 
