Any municipality that shall establish a library under the provisions of this article, or that has heretofore established a free public library pursuant to law, and has purchased or shall purchase lands, and has erected or shall erect buildings thereon, or both, for the purposes of a free public library, and has made or shall make appropriations therefor under this article, may make additional appropriation for the equipment, furnishing and decorating of the library building in manner following: The board of trustees shall certify to the board or body having charge and control of the finances of the municipality the amount necessary for the equipment, furnishing and decorating of the library building, and thereupon such board or body may by resolution, at its discretion and with the approval of the mayor or other chief executive officer of the municipality, make appropriation of such money and authorize and empower the board of trustees of the free public library to expend such sum of money. Upon the passage of such resolution the board of trustees may enter into contracts for such equipment, furnishing and decorating, and expend money therefor to the amount of the appropriation.