There shall be a department of purchases and supplies, the head of which shall be the city purchasing agent who shall be someone other than the director of finance. The purchasing agent shall make all purchases of supplies, materials and equipment for the city in the manner provided by ordinance and shall, under such regulations as may be provided by ordinance, sell, lease or otherwise dispose of property, real and personal, of the city not needed for public purposes or that may have become unsuitable for use, or that may have been condemned as useless by the city manager. He shall have charge of such general storerooms and warehouses of the city as the commission may by ordinance establish.