Chemical Abstracts Service Number
A Chemical Abstracts Service number (CAS number) is a number which is used to identify each unique chemical compound, polymer, biological sequence, mixture and alloy.
The Chemical Abstracts Service, 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.