“Reserving full power to me, at any time of my life, by any writing or writings under my hand, executed in legal and proper form, not only to revoke and alter these presents in whole or in part, but also to sell, alienate, or dispose the aforesaid lands, earldom, lordships, baronies, and others, or any part thereof, or to contract debt thereon, upon, or even gratuitously to dispose thereof, or burden the same as I shall think proper, as fully and freely as if these presents had never been granted; but declaring, that any alteration or revocation shall not be inferred by implication or construction.”