4Provided. that, in the case of cargoes of petroleum, it shall be lawful for the Commissioners not only to land the petroleum from all set-going vessels, but also by their servants or agents to put the petroleum out of the hold and overside such vessels:
Provided 1[further] that the Commissioners shall not be bound to land, ship or move any single article or package exceeding thirty tons of twenty hundredweight in weight except at such special charge as may be agreed on in respect of such article or package:
