duty on exports

a tax or duty on a bill of lading, although differing in form from a duty on the article shipped, is in substance the same thing; for a bill of lading, or some written instrument of the same import, is necessarily always associated with every shipment of articles of commerce from the ports of one country to those of another... A bill of lading, therefore, or some equivalent instrument of writing, is invariably associated with every cargo of merchandise exported to a foreign country, and consequently a duty upon that is, in substance and effect, a duty on the article exported.