A solution will usually separate into its individual compounds as they melt or boil at different temperatures. Check the ratios of the atoms. If they exist in exact integer ratios, the substance is a true chemical compound. Atoms are the smallest particles of matter that retain a distinct chemical behavior. First postulated by the ancient Greeks and confirmed by John Dalton in 1808, atoms are the basic unit of chemistry.
All stable substances are combinations of atoms.
Each kind of molecule with an exact integer ratio of atoms has a chemical behavior identical to all other molecules of the same type. As a result, we tend to analyze quantities of the same molecule by examining only a single molecule of the type. Having more of the same molecule makes no difference, each of them must behave exactly as any other of the same molecule. Methane is a compound with 4 atoms of hydrogen and one of carbon. Hydrogen peroxide is a compound with 2 atoms of hydrogen and 2 atoms of oxygen.