(1) Whenever cities having a population of twenty-five thousand or more, as determined by the last preceding federal decennial census, have moneys in policemen's or firefighters' pension funds, or other special funds of said cities, including pension, endowment, and trust funds, whether or not administered by a board or similar authority, it is lawful to invest or reinvest these moneys as set forth in this section if the authorization to invest moneys as provided in this section does not affect the administration of or control over the various funds, to wit:

(a) Class 1. Bonds, warrants, or checks of the United States, the state of Colorado, or in the bonds of any other state of the United States;

(b) Class 2. General obligation bonds of any city, town, or school district of the state of Colorado, the valuation for assessment of which city, town, or school district in the year next preceding the year in which such bonds may be purchased equals or exceeds two million dollars;

(c) Class 3. Obligations secured by first liens on real estate or by pledge of specific income or revenue and issued, insured, or guaranteed by any agency or instrumentality of the United States or the state of Colorado;

(d) Class 4. Notes, bonds, or debentures which are direct obligations of United States corporations engaged in the production, transportation, distribution, or sale of electricity or gas, or the operation of telephone or telegraph systems or water works, or any combination of them, which, at the time of purchase, are designated as investment grade securities by any two nationally recognized investment services as may, from time to time, be designated by the city council;

(e) Class 5. In share certificates for savings accounts in any state or federally chartered savings and loan association in Colorado if said association is a member of the federal deposit insurance corporation or its successor and further if the full amount of each account is insured by the federal deposit insurance corporation or its successor; and in any time certificate of deposit or savings account in any state or national bank in Colorado, which certificates of deposit or savings accounts are fully insured by the federal deposit insurance corporations or its successor;

(f) Class 6. In stocks, preferred or common, or bonds of corporations, created or existing under the laws of the United States, or any state, district, or territory thereof, which, at the time of purchase, are listed on a national stock exchange in the United States.

(2) Investments under this section shall be limited in their acquisition and retention in the above classes of securities so that the aggregate of all investments in each separate fund at any time shall be as follows:

(a) Classes 1, 2, and 3, or any combination thereof, up to any amount but not less than seventy percent;

(b) Class 4. In any amount not to exceed thirty percent;

(c) Class 5. In any amount that is fully insured by the federal deposit insurance corporation or its successor.

(3) The legal investments in this section authorized for cities having a population of twenty-five thousand or more shall be in addition to those investments otherwise by law authorized for said cities.

(4) Notwithstanding the provisions of subsection (2) of this section, investments of firefighters' pension funds shall be limited in their acquisition and retention in the classes of securities set forth in subsection (1) of this section so that the aggregate of all investments in each separate fund at any time shall be as follows:

(a) Classes 1, 2, and 3, or any combination thereof, up to any amount but not less than fifty percent;

(b) Class 4. In any amount not to exceed fifty percent, but not more than fifty percent of such class 4 aggregate may be invested in class 4 notes, bonds, or debentures which are convertible into shares of common stock or in common stocks of such class 4;

(c) Class 6. In any amount not to exceed fifty percent;

(d) As a further limitation thereon, in any amount not to exceed seven percent or one hundred thousand dollars, whichever is the greater, of any one issue valued at the time of purchase;

(e) In no event shall any investment be made in the common or preferred stock, or both, of any single corporation in an amount in excess of five percent of the then book value of the assets of the retirement fund.