In an experiment to determine the empirical formula of magnesium oxide, a student weighs an empty crucible then adds a strip of magnesium metal and reweighs the crucible. The crucible and magnesium are heated with a burner flame, which ignites the magnesium and forms a grey-white solid. After cooling, the crucible and solid are reweighed and the data are analyzed to give an empirical formula of ${\mathrm{Mg}}_5{\mathrm{O}}_4$. Which could account for the observed ${\mathrm{Mg}}_5{\mathrm{O}}_4$ result rather than the expected $\mathrm{MgO}$ ?