Section 267. Conveyances with power to revoke, determine or alter

A
  conveyance of, or charge on, an estate or  interest  in  real  property,
  containing  a  provision for the revocation, determination or alteration
  of the estate or interest, or any part  thereof,  at  the  will  of  the
  grantor,  is  void,  as against subsequent purchasers and incumbrancers,
  from the grantor,  for  a  valuable  consideration,  of  any  estate  or
  interest so liable to be revoked or determined, although the same be not
  expressly  revoked,  determined  or altered by the grantor, by virtue of
  the power reserved or expressed in the prior conveyance or charge. Where
  a power to revoke a conveyance of real property or the rents and profits
  thereof, and to reconvey the same, is given to any  person,  other  than
  the  grantor  in such conveyance, and such person thereafter conveys the
  same real property, rents or profits to a purchaser or incumbrancer  for
  a  valuable  consideration,  such subsequent conveyance is valid, in the
  same manner and to the same extent as if the power  of  revocation  were
  recited  therein,  and  the  intent  to  revoke  the  former  conveyance
  expressly declared. If a conveyance  to  a  purchaser  or  incumbrancer,
  under  this  section, be made before the person making it is entitled to
  execute his power of revocation, it is nevertheless valid, from the time
  the power of revocation actually vests  in  such  person,  in  the  same
  manner, and to the same extent, as if then made.