You can get the carbon content from the count and type of the other halogens as the structure of halogenated hydrocarbons follows a particular pattern. I don't have my Merck handy, but that is what I recall. Don't remember if halons are just single chain alkanes or what. I'll let you know when I get back from the telescope. John John Brownlee Lunar and Planetary Lab University of Arizona jonnie @ lpl . arizona . edu