The said city shall, by ordinance, make all necessary rules and regulations concerning the control and management of said fund to properly safeguard the same, but shall in nowise be liable for any of said funds except a misappropriation thereof, and shall not have power to bind the city or said fund for any further liability than whatever net interest may be actually realized from such investments, and shall not be liable to any particular person for more than the proportionate part of such net earnings.