b LIQUIDS THAT CONDUCT ELECTRICITY i First test liquids obtained by melting substances Melt the following substances but heat very gently and cautiously because otherwise they may ignite and burn sulphur wax naphthalene polyethylene material tin lead and if available a low melting point salt such as lead bromide mp 488oC or potassium iodide mp 682oC  Test the conductivity of the melt by dipping in the electrodes and waiting a few moments for the electrodes to reach the same temperature This ensures that the electrodes are in contact with the liquid and not the solidified melt Scrape and clean the electrodes between each test ii Test ethanol or methylated spirits acetone carbon IV chloride vinegar sugar solution copper II sulphate solution sodium chloride solution and other substances dissolved in water Clean and dry the electrodes between each test iii Test pure distilled water for conductivity Put the electrodes into a beaker of distilled water The bulb does not light up so pure water does not conduct electricity Very gradually stir small crystals of common salt into the water Note any changes to the bulb as the salt dissolves Classify substances into the following groups a those which conduct electricity in the solid state and those which do not b those which conduct in the liquid state and those which do not c those which conduct when dissolved in water and those which do not