The Chemical Abstracts Service (CAS), a subsidiary organization of the American Chemical Society, is responsible for assigning a CAS number to each substance appearing in literature. Its purpose is to avoid the trouble of having multiple names for chemical substances and make database searches more convenient. Nowadays, almost all chemical databases allow retrieval using CAS numbers.

The CAS Registry Number, also known as CAS Rn or CAS #, is a unique numerical identification number for a substance (compound, polymer material, biological sequences, mixture, or alloy).

The Chemical Abstracts Service (CAS), a subsidiary organization of the American Chemical Society, is responsible for assigning a CAS number to each substance appearing in literature. Its purpose is to avoid the trouble of having multiple names for chemical substances and make database searches more convenient. Nowadays, almost all chemical databases allow retrieval using CAS numbers.

CAS number inclusion quantity:
According to the official website of Chemical Abstracts in the United States, as of 17:20 on March 15, 2017, the number of chemicals included in CAS REGISTYSM has reached 129015486. In 2005, it was increasing at a rate of over 4000 species per day. In 2016, approximately 15000 new substances were added daily. And the total number of new substances added every day is still increasing. On a certain day in December 2016, 230000 new CAS numbers were added.

Precautions for CAS number retrieval:
In the search box, you can see that there are three query methods supported: CAS number, name, and chemical formula. When entering a certain type of character, it will be judged that the input is a CAS number, and the search will be conducted according to the good CAS method for characters! You can refer to the following example.
Firstly, entering nothing or only spaces: The search will be randomly conducted based on the first three digits of the CAS number as keywords.
Secondly, entering an incorrect CAS number, such as 00000 5-0, 50-010, 50-00-1, 40-11-, will result in a search based on the CAS number, and the search will display 0 most relevant results for you!
Thirdly, enter the beginning of a correct CAS number, such as 50-0, 50-00, 50-00-1 40000-: will be searched by CAS number and corresponding results will be obtained. For example, the search results for 40000- show you the 10 most relevant results.. For example, a search result of 40000 will display the 22 most relevant results for you. Observing the search results, it will be found that the CAS numbers in the results all start with the input string. For example, CAS number 400009-80-5 starts with 40000, and the number retrieved will not exceed 100!