The jurisdiction ceded as provided in Code Section 50-2-23 shall not vest until the United States has acquired the title to the lands by purchase, condemnation, or otherwise. As long as the lands remain the property of the United States when acquired by purchase, condemnation, or otherwise, and no longer, the same shall be and continue to be exempt and exonerated from all state, county, and municipal assessment, or other charges which may be levied or imposed under authority of the state.