Experiment C5.1.2.2 demonstrates the principle of the thermite process. In engineering, the thermite process is used to weld railway tracks together. A mixture of aluminium grit and iron(II, III) oxide is added to the apparatus and lit with an ignition rod. Liquid iron and aluminium oxide form in a very exothermic reaction. The iron has a higher density than aluminium oxide and so it sinks down in the melt.
Because aluminium releases immense quantities of energy in the reaction with oxygen, the reaction needs only to be started with an igniter. The energy released drives the rest of the process, and along with that it also liquefies the resulting iron.