No other tax upon express receipts, or upon the privilege of transacting express business, shall be collected without further authority of law to be hereafter enacted: Providing, That this act shall not be construed to repeal or take the place of the tax upon the capital stock now imposed by law; but the tax on gross receipts hereby imposed shall be in addition to the tax on capital stock imposed by existing law upon any of the corporations, companies or associations hereby taxed.
72 P.S. § 2202