The Chemical Abstract Service (CAS) is part of the American Chemical Society, and it is used to maintain a database of chemical compounds, substances, and alloys. The CAS database contains over 100 million different chemical compounds. Each CAS entry is identified by a specific number called CAS Registry Number (, 2018).

CAS Registry Number refers to a maximum of ten digits which are assigned to a compound when CAS registers a new compound. The digits are divided into three groups that are separated by a hyphen. The first group has 2 to 7 digits, the second has two digits, and the last group has one digit. The CAS Registry Number has no significance to the chemical nature of the compounds. It offers an alternative way of identifying a chemical instead of using its name. Various compounds have more than one name.

An example is ethanol which is also known as hydroxyethane, grain alcohol, absolute alcohol, ethyl hydrate, and ethyl alcohol. One CAS Registry Number 64-17-5 identifies all these names. CAS Registry Numbers, therefore, provides a useful way of identifying a compound over its name. The numbers are also used to distinguish between two or more stereoisomers of a compound. Glucose, for instance, exists in two forms, D and L. the two types of glucose have different CAS Registry Numbers (ThoughtCo, 2018).

CAS Registry Numbers do not depend on any system of chemical nomenclature. As seen from the above information, a CAS Registry Number is unique and specific to only one compound or substance regardless of several other ways the substances are described. Government agencies regularly use it because the CAS Registry Numbers are unique, can be validated quickly and reliably, and they are internationally recognized. The CASRN avoids confusion between compounds that have similar names or abbreviation and in chemicals that have multiple names (, 2018).

Earth Science Information Systems (EScIS) offer a free CAS number resource to help you search for CAS registry numbers. The free tool is used to access thousands of CAS numbers and Chemical Names in a searchable format.

Chemicals can be searched either by the chemical name, e.g. Lead, or by their CAS number, e.g. 1335-32-6. Where no CAS number exists for a chemical, an ESDat ChemCode is available. The searchable database includes over 5500 chemical names and CAS numbers.

For each chemical name and CAS code, links to further resources are available. These include NIST. (National Institute of Standards and Technology Standard Reference Database); Scorecard data (for information on pollutant problems and toxic chemicals); USEPA IRIS. (The United States Environmental Protection Agency Integrated Risk Information System); and IPCS INCHEM. (International Programme on Chemical Safety (IPCS) and the Canadian Centre for Occupational Health and Safety (CCOHS)). More information can be found at Name and CAS number.html.

About EScIS
EScIS provide environmental and groundwater database software, consultancy, advisory, programming, customisation, implementation, and training services. EScIS also develop and resell the ESdat suite of software. ESdat is used worldwide and is the most widely used environmental and groundwater data management and analysis package in the Asia / Pacific.

Name: Earth Science Information Systems (EScIS)
Contact: Trevor Pemberton
Address: Unit 4, 59 Centennial Circuit Byron Bay, NSW, 2481 Australia
Phone: +61 2 9232 8080
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