Ebook Central allows you to read a title the library does not own for 5 minutes before you are prompted to request full access.
You will be sent an email with the link to the full-text of the book. You can access the link for 7 days.
The 5 minute reading period is for you to 'look before you loan'. The Library is charged for each book that is viewed beyond this time. If you browse first, the Library is only charged for books that you actually want.