There shall be a county purchasing agent for the County of Cook who shall be appointed by the president by and with the consent of the Board of Commissioners. He shall hold office for one year and until his successor is appointed. No person shall be appointed county purchasing agent unless he has had at least three years experience in an executive capacity in the purchasing office of a private or public corporation whose purchases are reasonably comparable in size to those of the County of Cook. His salary shall be fixed by the Board of Commissioners. He shall give a bond for the due performance of his duties in an amount to be prescribed by the Board of Commissioners. The county purchasing agent shall have power to appoint, in accordance with civil service regulations, the necessary employees of his office and to prescribe their duties. The number and salaries of such employees shall be fixed by the Board of Commissioners.