Every power, beneficial or in trust, is irrevocable, unless an authority to revoke it is contained or reserved in the instrument creating the power.
(Code 1852, §1338; Code 1867, §1608; Code 1876, §2217; Code 1886, §1863; Code 1896, §1059; Code 1907, §3436; Code 1923, §6941; Code 1940, T. 47, §89.)