The following shall not take effect:
(1) Fideicommissary substitutions which are not made in an express manner, either by giving them this name, or imposing upon the fiduciary the absolute obligation to deliver the property to a second heir;
(2) Provisions which contain a perpetual prohibition to alienate, and even a temporary one, beyond the limit fixed in article 863;
(3) Those which impose upon the heir the charge of paying to various persons successively, beyond the limit prescribed in article 863, a certain income or pension;
(4) Those which leave to a person the whole or part of the hereditary property in order that he may apply or invest the same according to secret instructions communicated to him by the testator. (785a)