The Secretary of the Interior is hereby authorized and directed, 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 sulphur in lands belonging to the United States located in the States of Louisiana and New Mexico for a period of not exceeding two years: , That the area to be included in such a permit shall be not exceeding six hundred and forty acres of land in reasonably compact form.Provided