Whenever there shall be or remain in any special or temporary fund created or established by or under any law of the state of Idaho, a surplus or unexpended and unencumbered balance after the purpose or purposes for which such special or temporary fund was provided shall have been fully accomplished, the state controller shall transfer any such balance to the general fund of the state: provided, that where such balance shall consist, in whole or in part, of the proceeds of any bonds then outstanding, the same shall be transferred to the sinking fund provided for the redemption of such bonds.