The burgess and council, or town council, of each of the several boroughs of this Commonwealth are authorized, in the manner hereinafter provided, to levy and collect, in each and every year when necessary, an annual special tax, in addition to the taxes now allowed by law, to be assessed and collected for the general purposes, not exceeding two mills on each dollar of the assessed valuation of the borough as ascertained for county purposes.
53 P.S. § 49241