I'm of the understanding that by "Old Facebook Chat" you mean previous Facebook Chat History.
Facebook does not make your previous Facebook Chat history accessible after a period of time. There are two ways in which you can ensure that your Facebook Chat history is automatically saved for future reference.
Facebook does not support Italic on Facebook Chat at the moment. You can, however, use Bold and Italic by using special codes.
By typing stars (*) before and after your message you can make your instant message go bold e.g. *your text here*
Alternatively, by typing underline (_) before and after your message you can make … Read more
Facebook Chat can be accessed by signing into Facebook or using a Facebook instant messenger such as Chit Chat for Facebook.