6. Whenever within the meaning of said act the clerks and persons employed by the collector, naval officer, surveyor, and appraisers, or either of them, in any customs district shall be as many as fifty, any existing classification for the customs service shall apply thereto, and when the number of clerks and persons employed at any post-office shall be as many as fifty any existing classification of those in the postal service shall apply thereto; and thereafter the Commission will provide for examinations for filling the vacancies at said offices, and the rules will be applicable thereto. RULE XIII 1. The date of the reception of all regular applications for the classified departmental service shall be entered of record by the Commission, and of all other regular applications by the proper examining boards of the district or office for which they are made; and applicants, when in excess of the number that can be examined at a single examination, shall, subject to the needs of apportionment, be notified to appear in their order on the respective records. But any applicants in the several States and Territories for appointment in the classified departmental service may be notified to appear for examination at any place at which an examination is to be held, whether in any State or Territory or in Washington, which shall be deemed most convenient for them. 2. The Commission is authorized, in aid of the apportionment among the States and Territories, to hold examinations at places convenient for applicants from different States and Territories, or for those examination districts which it may designate and which the President shall approve. 3. The Commission may by regulation provide for dropping from any record the applicants whose names have remained thereon for six months or more without having been reached in due course for notification to be examined. RULE XVI. 1. Whenever any officer having the power of appointment or employment shall so request, there shall be certified to him by the Commission or the proper examining board four names for the vacancy specified, to be taken from those graded highest on the proper register of those in his branch of the service and remaining eligible, regard being had to any right of preference and to the apportionment of appointments to States and Territories; and from the said four a selection shall be made for the vacancy. But if a person is on both a general and a special register he need be certified from the former only, at the discretion of the Commission, until he has remained two months upon the latter. 2. These certifications for the service at Washington shall be made in such order as to apportion, as nearly as may be practicable, the original appointments thereto among the States and Territories and the District of Columbia upon the basis of population as ascertained at the last preceding census.