The Secretary of the Treasury shall receipt for moneys or securities composing trust funds given or bequeathed to the Board and shall invest, reinvest, and retain the moneys or securities as the Board from time to time determines. The Board may not engage in business or exercise a voting privilege which may be incidental to securities in such trust funds, nor may the Secretary of the Treasury make investments for the account of the Board which could not lawfully be made by a trust company in the District of Columbia, unless directly authorized by the instrument of gift or bequest under which the funds to be invested are derived, and may retain investments accepted by the Board.