cas号是什么
CAS号（CAS Registry Number或称CAS Number, CAS Rn, CAS #），又称CAS登录号，是某种物质（化合物、高分子材料、生物序列（Biological sequences）、混合物或合金）的唯一的数字识别号码。
美国化学会的下设组织化学文摘服务社（Chemical Abstracts Service, CAS）负责为每一种出现在文献中的物质分配一个CAS号，其目的是为了避免化学物质有多种名称的麻烦，使数据库的检索更为方便。如今几乎所有的化学数据库都允许用CAS号检索。
到2012年1月20日，CAS已经登记了64,944,800余种物质最新数据，并且还以每天4,000余种的速度增加。
CAS登录号是美国化学文摘服务社(Chemical Abstracts Service ,CAS)为化学物质制订的登记号，该号是检索有多个名称的化学物质信息的重要工具。是某种物质（化合物、高分子材料、生物序列[Biological sequences]）、混合物或合金的唯一的数字识别号码。
格式
一个CAS编号以连字符“-”分为三部分，第一部分有2到7位数字，第二部分有2位数字，第三部分有1位数字作为校验码。CAS编号以升序排列且没有任何内在含义。
校验码的计算方法如下：CAS顺序号（第一、二部分数字）的最后一位乘以1，最后第二位乘以2，依此类推，然后再把所有的乘积相加，再把和除以10，其余数就是第三部分的校验码。
举例来说，水（H2O）的CAS编号前两部分是7732-18，则其校验码= ( 8×1 + 1×2 + 2×3 + 3×4 + 7×5 + 7×6 ) mod 10 = 105 mod 10 = 5（mod是求余运算符）
以上内容参考 百度百科-CAS登录号
美国化学会的下设组织化学文摘社（Chemical Abstracts Service，简称CAS）。该社负责为每一种出现在文献中的物质分配一个CAS编号，这是为了避免化学物质有多种名称的麻烦，使数据库的检索更为方便。
CAS registry numbers are unique numerical identifiers for chemical compounds, polymers, biological sequences, mixtures and alloys. They are also referred to as CAS numbers or CAS RNs.
Chemical Abstracts Service (CAS), a division of the American Chemical Society, assigns these identifiers to every chemical that has been described in the literature. The intention is to make database searches more convenient, as chemicals often have many names. Almost all molecule databases today allow searching by CAS number.
As of Nov 2, 2005, there were 26,901,696 substances in the CAS registry — the current number is published here. About 4,000 new numbers are added each day.
CAS registry number is separated by hyphens into three parts, the first consisting of up to 6 digits, the second consisting of two digits, and the third consisting of a single digit serving as a check digit.
2。 UN no. 才是危险品特有的。 运输都要有这号码。
UN numbers or UN IDs are four-digit numbers that identify dangerous goods hazardous substances and articles (such as explosives, flammable liquids, toxic substances, etc.) in the framework of international transport. Some hazardous substances have their own UN numbers (e.g. acrylamide has UN2074), while sometimes groups of chemicals or products with similar properties receive a common UN number (e.g. flammable liquid, not otherwise specified, have UN1993). A chemical in its solid state may receive a different UN number than the liquid phase if their hazardous properties differ significantlysubstances with different levels of purity may also receive different UN numbers.
UN numbers range from UN0001 to about UN3500 and are assigned by the United Nations Committee of Experts on the Transport of Dangerous Goods. They are published as part of their Recommendations on the Transport of Dangerous Goods, also known as the Orange Book. These recommendations are adopted by the regulatory organization responsible for the different modes of transport.
NA numbers (North America), also known as DOT numbers are issued by the United States Department of Transportation and are identical to UN numbers, except that some substances without a UN number may have an NA number. These additional NA numbers use the range NA8000 - NA9999.
Associated with each UN number is a hazard identifier, which encodes the general hazard class and subdivision (and, in the case of explosives, their compatibility group). For instance, the hazard identifier of acrylamide is 6.1 and the one of cigarette lighters is 2.1. If a substances poses several dangers, then subsidiary risk identifiers may be specified. It is not possible to deduce the hazard class(es) of a substance from its UN number: they have to be looked up in a table.
The hazard classes and their divisions are:
Class 1: Explosives
Division 1.1: Substances and articles which have a mass explosion hazard
Division 1.2: Substances and articles which have a projection hazard but not a mass explosion hazard
Division 1.3: Substances and articles which have a fire hazard and either a minor blast hazard or a minor projection hazard or both, but not a mass explosion hazard
Division 1.4: Substances and articles which present no significant hazard
Division 1.5: Very insensitive substances which have a mass explosion hazard
Division 1.6: Extremely insensitive articles which do not have a mass explosion hazard
Class 2: Gases
Division 2.1: Flammable gases
Division 2.2: Non-flammable, non-toxic gases
Division 2.3: Toxic gases
Class 3: Flammable liquids
Class 4: Flammable solidssubstances liable to spontaneous combustionsubstances which, on contact with water, emit flammable gases
Division 4.1: Flammable solids, self-reactive substances and solid desensitised explosives
Division 4.2: Substances liable to spontaneous combustion
Division 4.3: Substances which in contact with water emit flammable gases
Class 5: Oxidizing substances and organic peroxides
Division 5.1: Oxidizing substances
Division 5.2: Organic peroxides
Class 6: Toxic and infectious substances
Division 6.1: Toxic substances
Division 6.2: Infectious substances
Class 7: Radioactive material
Class 8: Corrosive substances
Class 9: Miscellaneous dangerous substances and articles
