A CAS Registry Number,also referred to as CASRN or CAS Number, is a unique numerical identifier assigned by the Chemical Abstracts Service (CAS) to every chemical substance described in the open scientific literature (currently including all substances described from 1957 through the present, plus some substances from the early or mid 1900s), including organic and inorganiccompounds, minerals, isotopes, alloys and nonstructurable materials (UVCBs, of unknown, variable composition, or biological origin).The registry maintained by CAS is an authoritative collection of disclosed chemical substance information. It currently identifies more than 144 million unique organic and inorganic substances and 67 million protein and DNA sequences,plus additional information about each substance. It is updated with around 15,000 additional new substances daily.（information coming from wikipedia.org)