The Central Government may, by notification in the Official Gazette, declare what gratuities shall be allowed to masters of ships, not being mail ships, in respect of postal articles received by them for conveyance on behalf of the Post Office; and the master of a ship, not being a mail ship, about to leave any port in ¹[India] as aforesaid shall, if he receives on board a mail bag for conveyance, be entitled to demand and obtain immediately the amount of the gratuity payable under this section in respect of the mail bag and its contents.