All money or property received by the board for any purposes of the fund under any law other than this law, or as gifts, grants, or bequests or in any manner other than as provided in this Article, shall be placed in this reserve and used for the purposes of the fund as the board decides; provided that, whenever any gift of moneys or other property is made to this reserve to be used for the benefit of any class of beneficiaries of this fund, such moneys or other property shall be used only for such specified purpose. The balance in this reserve shall be annually improved by interest at the rate realized by the Board on its investments in the previous year.
40 ILCS 5/6-202