Dave Bryant, quite correct; you generally add a small amount of salt (NaCl, sodium chloride), which does reduce the resistance. If you add a lot of salt, as I did when performing this experiment at school, you get chlorine rather than oxygen at the anode. And yes, you get chlorine and hydrogen in exactly the right proportions to create hydrochloric acid, with a heck of a bang, when you toss a lighted taper into the glass jar in which you have collected both gasses.


Not really part of my childhood, but I have this knack for making laboratories uninhabitable. Years later, when studying Mining Geology at University, I was testing for a mineral named "Pyrrhotite", an important ore of nickel. The test notes said, "Add sulphuric acid to powdered sample". I poured half a pint of acid over several ounces of pure pyrrhotite, and turned the page to read, "If pyrrhotite is present in significant quantities, copious volumes of H2S are evolved". H2S is of course, sulphuretted hydrogen, the very poisonous gas which produces the awful "rotten eggs" smell.

Years ago, my father managed to coat the inside of a lab at Durham University with bakelite, which had to be laboriously removed over several days from benches, sinks, gas taps, plug sockets, lights etc. He refused to tell me quite how, in case I was tempted to repeat the experiment.