The [[Chemical Abstracts Service]] (CAS), a division of the American Chemical Society, assigns unique identifiers to every different chemical. Most molecule databases today permit searching for a compound by entering its CAS number. There are over 30 million CAS numbers as of May 2007. | The [[Chemical Abstracts Service]] (CAS), a division of the American Chemical Society, assigns unique identifiers to every different chemical. Most molecule databases today permit searching for a compound by entering its CAS number. There are over 30 million CAS numbers as of May 2007. |