CAS: An assistant for retrieval of chemicals It’s quite helpful for salesmen engaged in fine chemical industry to know well physical and chemical property of the products. The information of numerous chemicals is available on the website of National Institute of Standard and Technology (NIST). The precise method to search for the interested product on NIST is to provide CAS number of this substance. CAS numbers is unique numerical identifier assigned by the Chemical Abstracts Service (CAS) to every chemical including elements, isotopes, organic and inorganic compounds, organometallics, metals, alloys, coordination compounds, minerals, and salts; as well as standard mixtures, compounds, polymers; biological sequences including proteins & nucleic acids; nuclear particles, and nonstructurable materials (aka 'UVCB's- i.e., materials of Unknown, Variable Composition, or Biological origin). They are also referred to as CAS RNs, CAS Numbers, etc.
A CAS number is separated by hyphens into three parts, the first consisting of up to 7 digits, the second consisting of two digits, and the third consisting of a single digit serving as a check digit. The check digit is found by taking the last digit times 1, the previous digit times 2, the previous digit times 3 etc., adding all these up and computing the sum modulo 10. For example, the CAS number of water is 7732-18-5: the checksum 5 is calculated as (8×1 + 1×2 + 2×3 + 3×4 + 7×5 + 7×6) = 105; 105 mod 10 = 5.