Encyclopedia Gallifreya

The  was a series of books, in the form of purple liquid in bottles, with at least eleven volumes. Instead of being read, voices could be heard from within the bottles. The Eleventh Doctor owned a copy which he kept in his TARDIS library.

When Clara Oswald hid in the library to escape the time zombie that was following her, volume four of the series began to spill. The vapour contained in the volume floated around the room, and voices speaking were heard. (TV: Journey to the Centre of the TARDIS)

Behind the scenes

 * The name was likely a Gallifreyan play on the Encyclopaedia Brittanica.
 * On the BBC's official Doctor Who site, the work takes the older British spelling of Encyclopaedia Gallifreya.
 * The vapour-like nature of the books resembles the fiction mists mentioned by the Doctor in TV: Silence in the Library.