I have yet to understand why the entire battery needs to be submerged in salt water when just dipping the gold plated battery plug into the water till discharged should be sufficient. Dan's method is best though!
Thurmond
That is a good question that I have wondered about too. I suppose having a submerged fire is safer than having it on your bench... but have you ever seen hydrogen and oxygen burn? Just say
Hindenburg!
Further science... Electrodes submerged in salt water produce two of the most explosive gasses. The cathode wire produces pure hydrogen and the anode produces pure oxygen. You have all the makings of an explosion. Capture the oxygen and hydrogen, mix and give it a combustion source like a little heat!
But salty water isn't usually conductive enough to produce enough current flow to generate the heat necessary for combustion, unless your salt water was really really salty.
Best to stick with the light/resistor to drain the battery for a day and then twist the leads together.
Science Project
Here is a great science project that I tried to get my kids to do for science fair. We understand that water does not conduct electricity unless it is a solution with ions. Did you know that you can determine, with quite a bit of accuracy, the concentration of salt in water using a ohm meter? By adding salt to water the resistance goes down. You can make a standard curve with known amounts of salt in water plotting resistance to amount of salt. For this to work the electrodes placed in the water must be kept the same distance apart so you can affix two wires to a stick with hot glue. Dip it in the water and that will tell you the resistance. Plot the reading against your standard curve and presto, you can know the concentration of salt. The project I wanted my kids to do was to measure the salt concentration over a years time in the lake and water gathering spots near our house. Road salt in the winter causes the concentration to skyrocket, but I don't know if anyone is keeping tabs on it.
Where was I going with this? Oh, yeah, someone could measure the resistance of the 12v car light and determine how much salt to add to a cup of water to have the equivalent resistance. You would still have to deal with a salt brine and electrode corrosion, but it could be done. Hook a battery plug up to some 14 AWG wire to dip in the brine and scrape off the crude every once in a while. Should bubble good too. Only do this in an area where the hydrogen and oxygen can float away and not accumulate.
Sorry - Science geek in me coming out.
