I’m not sure it would comply with modern OSHA rules, so whatever you do, make sure you don’t touch any of the exposed conductors. But if you need to quickly come up with a low voltage, this self-explanatory method of making your own resistor should do the trick. Measure the voltage, and keep adding salt until you get the desired voltage.

The idea appeared in the August 1945 issue of Radio Craft.  It had been sent in to the magazine by one Ollie Peoples of Mountain View, Oklahoma, who pointed out that if you can’t reach the desired voltage, then use a larger glass and add more salt.  He reported that the average glass wouldn’t deliver more than six volts, and would get unduly hot with that voltage.

As long as they’re careful with the high voltages involved, advanced students could use this idea as part of an interesting science fair project, demonstrating how changes in salinity affect the resistance.