Chemistry is the analysis of materials to determine both what element or groups of element in a given substance (qualitative analysis)and how much of each present(quantitative analysis). Chemists often must depend on the observation of the chemical properties of substances in order to make an identification, just as a detective often must depend on the observation of the behavior of individuals suspected of being involved in a crime. The chemist may look for clues concerning the identity of a substance by observation of pH, color, odor, viscosity, and the results of mixing two substances.