If any of the lands purchased or to be purchased by the United States under the provisions of the Act approved March 1, 1911, as amended, within the limits of townships 1, 2, and 3 north, ranges 9, 10, 11, 12, and 13, in Forest and Perry Counties, State of Mississippi, are determined to be chiefly valuable and necessary for a National Guard encampment and related military purposes, the Secretary of Agriculture may, and he is, authorized to convey full title to said lands to the State of Mississippi or the Department of the Army: Provided, That there is paid into the Treasury of the United States, or made available by transfer on the books of said Treasury, sums of money equal to the full amounts expended by the Department of Agriculture for the purchase of said lands, and the money so paid into or transferred on the books of the Treasury shall be available for expenditure by the Secretary of Agriculture for the purchase of other lands under the provisions of said Act of March 1, 1911, as amended.