# CAS registry number

The CAS number (also CAS registration number and CAS Registry number, Eng. CAS Registry Number, CAS = Chemical Abstracts Service ) is an international standard designation for chemicals. For each known chemical substance (including biological sequences, alloys, polymers), there exists a unique CAS Registry Number. Sum formulas ( different languages ) Trivial names and even IUPAC names are not unique and can lead to confusion especially to non- chemists. Various isomers ( eg, enantiomers or diastereomers) of a molecule carry different CAS numbers. For some technically important mixtures (eg, mixtures of isomers, such as racemates ) have also been specially CAS numbers assigned.

## Construction

CAS numbers consist of three numbers, separated by two hyphens. The first number can be up to seven digits, and the second number of two digits. The numbers are encoded with a checksum - this is the third number - and thus relatively easy to check for plausibility. They are assigned in ascending order and contain no internal order. On 8 September 2009, the fifty millionth substance has been registered. Together with more than 61 million sequences over 111 million numbers were issued to someone else. Approximately 12,000 new substances are registered daily.

CAS numbers are assigned by the Chemical Abstracts Service, a administered by the American Chemical Society Institution based in Columbus, Ohio, USA since 1965. Use of the CAS Registry database in which reference is made to any chemical structure using the CAS number is chargeable.

## Testing of CAS numbers

A CAS Registry Number is a sequence of digits of n decimal digits in the general form:

With a check digit and each represents a decimal digit.

A CAS number is correct when

So the weighted sum of the digits to the radical R 10 can be carried.

With "mod 10 " here is not the test procedure modulo 10 ( Luhn algorithm) meant, but it is by this we understand the last digit of the sum result. Mathematically seen:

10 · { sum result: 10 - ( rounded to integer [ Total Score: 10 ] ) } = check digit R.

With total earnings " weighted sum of the digits up " is the term above meant.

### Example calculation

CAS number for ethanol is 64-17-5.

With the condition is satisfied.

## Examples

- Water - CAS: 7732-18-5
- Ethanol - CAS: 64-17-5
- Acetylsalicylic acid ( active ingredient of Aspirin ® ) - CAS: 50-78-2
- Caffeine - CAS: 58-08-2
- Amphetamine- [1:1 - mixture (racemate ) of (R) -amphetamine, and ( S) -amphetamine ] - CAS: 300-62-9