Test if a solution conducts electrical currents:
Fill a cup with salty water or other ionic solution, and then rest the device on the rim of the cup (make sure the aluminum leads are immersed in the solution). If the light bulb glows brightly, then the solution is very conductive. If it barely glows—or not at all—then your solution is not very conductive.
Test a series of solutions (try solutions with varying concentrations of electrolytes):
Fill each cup to the same height with solutions containing varying amounts of salt. Rest the device on the rim of each cup, one after the other (make sure the leads are immersed in the solutions at the same depth—this will keep the contact area the same for each solution tested). Compare how the light bulb glows in each of the solutions.
Test to see if a chemical reaction is occurring:
Fill a cup with a salt solution and then place your device on the rim of the cup. Watch the aluminum leads and see what develops. Do you notice a color change or gas at one of the aluminum leads? Do you see your solution getting cloudy or detect an odor emanating from the cup? These and other subtler features may indicate that a chemical change or reaction is happening.