The officer collecting the taxes levied under Section 8-3-1 shall settle with and pay over to the municipal treasurer, or, in the case of a tax levied for library purposes in municipalities having not to exceed 50,000 inhabitants, to the board of trustees of the library, as often as once in 2 weeks from the time he commences the collection thereof, all taxes he has then collected, till the whole tax collected is paid over. The expenditures of taxes levied for library purposes, whether expended by the municipal treasurer or by the board of library trustees shall be made pursuant to the direction of the board of library trustees.