A CAS Registry Number (often abbreviated as CAS RN or CAS Number) is a unique, unambiguous numerical identifier assigned to a single chemical substance by the Chemical Abstracts Service (CAS), a specialized division of the American Chemical Society (ACS).
Introduced in 1965, this system acts as a universal “chemical ID card”. It provides a foolproof way to identify a compound regardless of its complex scientific nomenclature, trade names, language barriers, or common synonyms. For instance, whether a substance is called “water,” “dihydrogen monoxide,” or “eau,” its definitive identity is locked into a single identifier: 7732-18-5. Anatomy of a CAS Number
A CAS Number contains up to 10 digits divided into three parts by hyphens. It is assigned sequentially as new substances are discovered, meaning the number itself carries no intrinsic structural meaning or scientific properties. The First Part (Left): Contains between 2 to 7 digits. The Second Part (Middle): Always contains exactly 2 digits.
Leave a Reply