What exactly is a CAS #? And how could you look one up for a chemical?
The chemical abs number is a number first devised I believe by the American Chemical Soc in order to give each chemical a unique number. It is is not used much, but can be useful. To find a CAS number or find what chemical it refers to go to www.sigmaaldrich.com and navigate through to the main screen. You will see a box marked product search in which you can enter a chemicals name, formula or number.
PubChem can be used to search for a compound by CAS number or by name. If you search by name the CAS number is given as the ‘registry number’.
CAS numbers are also given to more complex entities. Doing a structural search in SciFinder can give lots of hits for various salts, specific stereochemistry, and so on, each with their own CAS number.