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( CAS registry number)
CAS registry numbers are unique numerical identifiers for chemical compounds, polymers, biological sequences, mixtures and alloys. They are also referred to as CAS numbers, CAS RNs or CAS _s. CAS also maintains and sells a database of these chemicals, known as the CAS registry. A CAS registry 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 numbers are assigned in increasing order and do not have any inherent meaning. The checksum is calculated by taking the last digit times 1, the next digit times 2, the next 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 is calculated as (8×1 + 1×2 + 2×3 + 3×4 + 7×5 + 7×6) = 105; 105 mod 10 = 5. The Chemical Abstracts Service has announced on its web site that it will add an additional digit to new CAS registry numbers, starting about January 2008.
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