Chemicals giant Imperial Chemical Industries (ICI) was formed by the merger of several chemical industry companies producing a wide variety of products, may of which were used in the production of further chemical products by other parts of the groups.
In addition to it's familiar use in domestic cooking Salt (Sodium Chloride) is used as a feedstock for a number of chemical production processes, but being soluble in water needs to be well protected from the weather while being transported. These covered salt vans were based on the standard coal wagon designs with a simple ridge roof added, providing much better rain protection than a simple tarpaulin sheet and due to their specialist use many remained in service until replaced wagons to modern design in the 1960s.