To encourage industrial expansion and development in the City of Frederick, the board of aldermen by a general ordinance is authorized to exempt from taxation for municipal purposes the buildings and equipment owned and operated by any manufacturing company or association within the corporate limits of the city. Any exemption from taxation under the provisions of this section shall be extended to all manufacturing companies and associations within the city engaged in the branch of manufacturing which will benefit by any such exemption. (Acts 1951, Ch. 539, § 110)