i Test the conductivity of solids by making a good contact between the surface of the solid and the two electrodes The surface of the solid must first be cleaned All metals conduct electricity Carbon conducts electricity Note whether nonmetallic solids eg plastics naphthalene wax sugar sodium chloride and sulphur conduct electricity ii Glass can be a conductor Heat a glass rod until it becomes very hot and begins to soften Test the hot soft part with the conductivity apparatus When molten glass is a good conductor of electricity