Complex sentence: For example, a cargo of aluminum ingots, which were not packaged for shipment, would be heavy and dense, so the customary freight unit for aluminum ingots would be the long ton, a measurement of weight.
Split into simpler sentences: For example, a cargo of aluminum ingots, which were not packaged for shipment, would be heavy and dense. Hence the customary freight unit for aluminum ingots would be the long ton, a measurement of weight.