Appearance
CAS-number β
CAS-number
The Chemical Abstract Service index number is a unique numeric identifier, designates only one substance, has no chemical significance, is a link to a wealth of information about a specific chemical substance. It includes up to 10 digits which are separated into 3 groups by hyphens. The first part of the number, starting from the left, has up to 6 digits; the second part has 2 digits and the final part consists of a single check digit.
CAS-numbers are produced by the Chemical Abstract Service, a division of the American Chemical Society (http://www.cas.org). The CAS Registry Number is a Registered Trademark of the American Chemical Society. The structure of the CAS-number is explained below.
For a limited number of substances, the same CAS-number applies to different appearances where the hazard aspects are different. For example, of acids and solutions of acids, or SiliconCarbide (with forms of non-fibrous, fibrils and whiskers). A different Index number may therefore have been assigned by the EU. Sometimes a different CAS number is used for a different appearance. Where this is not the case, we have changed the last digit of the CAS number (the 'checksum') to '%', 'i' or 'j' for the other forms. The '%' is used for 'solutions of ..', for example Hydrochloric acid with CAS number 7647-01-0 (with Index number 017-002-00-2) and and "Hydrochloric acid ..% solution" with CAS number 7647-01-% (with Index number 017-002-01 -X).
For a limited number of substances the same CAS-number applies to the pure substance and to the substance in an aqueous solution (the European Union has assignedin that case two different Index-numbers). To avoid problems with the uniqueness of the CAS-number we have chosen fore these situations to change the last digit of the CAS-number (a checksum) to the %-sign. F.i.: the CAS-number for Hydrogen chloride is 7647-01-0 (with Index-number 017-002-00-2), and has Hydrochloric acid ... % been assigned the CAS-number 7647-01-% (with Index-number 017-002-01-X).
When a substance does not have a CAS-number, the CAS-number field is otherwise used to identity the substance:
- If the substance has an EC-number, but not an CAS-number, the 'pseudo-CAS-number' is: EC#######.
- If the substance has not an CAS-number and not an EC-number, but has an EU Index-number, the 'pseudo-CAS-number' is: ID#######.
- If a substance does not have a CAS number or another 'pseudo CAS number', but does have a REACH registration dossier, DIS ###### is used.
- If a substance does not have a CAS number or another 'pseudo-CAS number', but it does appear on the candidate list of substances of very high concern for authorization (in accordance with Article 59 (10) of the REACH Regulation), SVHC#### is used.
- If a substance occurs in the Australian version of GHS (AICIS; Australian Industrial Chemicals Introduction Scheme), but does not have a CAS number or another 'pseudo-CAS number', AUS####### is used.
- If the substance has not an CAS-number, nor an EC-number, nor an Index-nunmber, a WGM-number is used as 'pseudo-CAS-number' (Note: WGM = Working Group Limit Values and Measurement Methods [WGM in Dutch] of the Duch Occupational Hygiene Society [NVvA])
The following formats of WGM-numbers are used:
WGM-H### : Wood
WGM-I### : IARC-classifications
WGM-V### : REACH exempted
WGM-#### : For other substances
Structure of the Chemical Abstract Service index number.
The CAS-number may be written in a general form as:
Ni .. N4N3-N2N1-R
In which R represents the check digit and N represents a fundamental sequential number. The check digit is derived from the following formula:
In which Q represents an integer which is discarded.
For example CAS# 107-07-3, the validity is checked as follows:
Q = 3 is discarded and R (the check digit) = 3.