Whenever any such treasurer or other authorized financial officer mentioned in § 6 shall have in his possession any uninvested monies or other funds belonging to any of the sinking funds referred to in § 6, it shall be his duty to deposit the same in some safe banking institution or trust company located in the State of Maryland, pending investment or reinvestment, and it shall be his duty to demand from any such banking institution or trust company adequate security for so much of said deposits as shall exceed the guarantee of the Federal Deposit Insurance Corporation, which security may consist of any of the classes of securities referred to in § 6 as suitable for investment of such sinking fund or may consist of a surety bond of some responsible corporate surety company qualified to do business in the State of Maryland, and no such deposit shall be made unless the security herein described shall be given.