The Secretary of the Interior is hereby authorized, under such rules and regulations as he may prescribe, to grant to any qualified applicant a prospecting permit which shall give the exclusive right to prospect for chlorides, sulphates, carbonates, borates, silicates, or nitrates of sodium, in lands belonging to the United States for a period of not exceeding two years: Provided, That the area to be included in such a permit shall not exceed two thousand five hundred and sixty acres of land in reasonably compact form.