Iron and sulphur. Image 1 of 3. Iron (left) is a dense magnetic metal while sulphur (right) is a less dense, non-magnetic non-metal. These elements can be used to demonstrate the difference between a physical and a chemical change. Mixing the two powders (see A500/594) is a purely physical change: the elements retain their properties and can be easily separated. A magnet could be used to pull away the iron, or the mixture could be tipped into water, causing the iron alone to sink. If the elements are heated together, however, a chemical change occurs and they react to form iron sulphide (see A500/595). This compound's properties are unlike those of its consituent elements.