AQUEOUS RHEOSTAT AND HEATING
by the Boom
THE SALT WATER RHEOSTAT--
Set up a circuit with switch, large clear glass light bulb (ie 300 watt), or several smaller bulbs in parallel (the board in ELECTRICAL CIRCUITS is ideal), the 120 volt source and the following rheostat:
The aqueous rheostat is a 500 ml beaker containing dilute salt water, and a pair of electrodes that you can raise and lower into the solution. The electrodes can be pieces of metal (screwdrivers are nice because of their insulated handles), or carbons from flashlight cells.
Connect the electrodes in series with your light bulb(s). (Be sure your bulbs are in parallel for maximum load on the circuit).
Raising and lowering the electrodes into the solution will cause the lights to vary their intensity, and illustrate the principle of ionic solution conduction and surface area of contact to vary resistance.
This principle was used in 1946 to control the lights in the Boomer Gambling Palace, a somewhat dubious operation in the grandfather's basement, whose objective was for the 9th graders to relieve the loose change from the underclassmen.
The above usage led to another discovery. That soon the solution became heated by the current flow of many lights. The intensity of the lights increased as the temperature rose. Then the lights began to flicker as a result of the rheostat's commencing to boil.
So here is another neat demo with this apparatus:
ZEE QUEEK BOIL
Increase the concentration of the salt solution, connect the electrodes directly to the AC switch, immerse the electrodes all the way, be sure that they do not touch each other, and let 'er ROAR. We should have quick boil in a matter of seconds. If your circuit breaker kicks out, dilute the salt solution (always know where your breaker is located).
This principle was used some years back in high speed egg cookers and baby bottle warmers.