Source : Webster's Revised Unabridged Dictionary (1913)

Ex- \Ex-\
   A prefix from the latin preposition, ex, akin to Gr. 'ex or
   'ek signifying out of, out, proceeding from. Hence, in
   composition, it signifies out of, as, in exhale, exclude;
   off, from, or out. as in exscind; beyond, as, in excess,
   exceed, excel; and sometimes has a privative sense of
   without, as in exalbuminuos, exsanguinous. In some words, it
   intensifies the meaning; in others, it has little affect on
   the signification. It becomes ef- before f, as in effuse. The
   form e- occurs instead of ex- before b, d, g, l, m, n, r, and
   v, as in ebullient, emanate, enormous, etc. In words from the
   French it often appears as es-, sometimes as s- or ['e]-; as,
   escape, scape, ['e]lite. Ex-, prefixed to names implying
   office, station, condition, denotes that the person formerly
   held the office, or is out of the office or condition now;
   as, ex-president, ex-governor, ex-mayor, ex-convict. The
   Greek form 'ex becomes ex in English, as in exarch; 'ek
   becomes ec, as in eccentric.