Section 3. That for the purpose of squaring the said Hunting park, and making the same more suitable in shape for use as a park, the park commissioners may negotiate with the owner of ground on the east side of said Hunting park, and south side of Bristol street, and acquire the title to an area of ground, at least as large as all that part of the said Hunting park situate north of the line of said Bristol street, which latter ground shall be given in exchange for the ground so acquired east of the said Hunting park and south of said Bristol street; and a deed or deeds, so agreed to be given in even exchange to the person entitled to receive the same, shall be executed by the mayor of the city of Philadelphia, whenever he shall be requested so to do by the park commissioners; and the said exchange to be made on or before the first day of January, one thousand eight hundred and seventy two.