No corporation now incorporated under the laws of this state, or which shall hereafter be incorporated thereunder shall exercise the right of eminent domain as against the land now occupied by any building which was used during the colonial or revolutionary period as a place of assembly by the council of the colony of Pennsylvania, or by the supreme executive council of the commonwealth of Pennsylvania, or by the congress of the United States; or as against the land now occupied by any fort, redoubt, or blockhouse erected during said colonial or revolutionary period; or as against any building used as headquarters by the commander-in-chief of the continental army; or as against the site of any such building, fort, redoubt, blockhouse or headquarters, which said building, fort, redoubt, blockhouse or headquarters, or site thereof, is now or shall hereafter be preserved for its historic memories and associations, and not for private profit: Provided, That the said Colonial and Revolutionary period, as applied to the buildings, forts, redoubts, blockhouses or headquarters, or the sites thereof, as aforesaid, shall be taken as ended on the third day of September, Anno Domini one thousand seven hundred and eighty-three.