For the survey of the public lands lying within the limits of land grants made by Congress to aid in the construction of railroads, and the selection therein of such lands as are granted therefor, to enable the Secretary of the Interior to carry out the provisions of section 894 of this title, the sum of $100,000 heretofore appropriated is made a continuing appropriation for the survey of lands within the limits of railroad land grants, and any money which shall be expended of such appropriation and reimbursed and paid into the Treasury is reappropriated, and said sum shall remain a continuing appropriation, and so often as any part of the same shall, after being expended, be reimbursed by any railroad company as hereinafter provided, the same shall be again available for the purposes aforesaid: Provided, That any portion of said sum expended for surveying such lands shall be reimbursed by the respective companies or parties in interest for whose benefit the lands are granted, according to the provisions of section 881 of this title: And provided further, That whenever there shall have been reimbursed and paid into the Treasury of the United States, by the respective companies or parties in interest, any part of said appropriation expended for surveys within such grants, there shall be immediately available, out of any money in the Treasury not otherwise appropriated, an amount equal to the amount so reimbursed, and the same shall be available for the survey of the public lands lying within the limits of the railroad land grants made by Congress, until all of said lands shall have been surveyed: Provided, That nothing herein contained shall be construed to prevent the use, within the limits of any railroad land grant made by Congress, of any part of any regular appropriation for surveying the public lands: Provided, That no part of the foregoing money shall be used for any land embraced in any grant to the State of Florida: And provided further, That the provisions of law requiring reimbursements to be made to the United States by railroad corporations claiming such grants shall apply equally to the successors of such railroad corporations acquiring title to their lands and other property, under decree of foreclosure of any mortgage authorized by Congress.