The county board of any county having more than two hundred thousand population may use money available in any fund of the county, if not presently or in the immediate future needed for the use of such fund, with which to take up, as an investment, legal valid warrants drawn upon any other fund of the county in which there may not be money presently available with which to pay such warrant; but such taking up of a warrant shall constitute and be deemed a purchase thereof, as an investment of idle money in the fund for which acquired. Any warrant, so taken by way of investment, shall be registered to the credit of the fund from which the money was taken with which to acquire the warrant and shall not draw interest.