In counties of the second class, all county taxes after the same become delinquent, as now provided by law, shall bear interest from the time said taxes become delinquent at a rate determined by the county commissioners not to exceed twelve per centum per annum until paid, and it shall be the duty of the collector of delinquent taxes to collect such interest in addition to the tax and pay the same into the county treasury.
72 P.S. § 5648