Every person who now has or shall hereafter acquire, or does or shall claim to have acquired, title to any real estate by twenty-one years' adverse possession, under the provisions of the act of twenty-sixth March, one thousand seven hundred and eighty-five, and the several supplements thereto, and shall not be in the possession of the said real estate, shall, within six months from the time of withdrawing from or being out of the said possession, file in the recorder's office of the county where the said real estate is situate a written statement of his claim, by him subscribed and sworn to, in substance as follows, viz.:
68 P.S. § 81