Visit to the LHS.

[doctorwayne]

And that covered hopper is for carbon black - not sure why, but they all had multiple small hatches. From what little I've seen written about it, it's either a very fine powder or sometimes pelletised, and is loaded and unloaded with specialised equipment, since it can be easily contaminated by many other substances.
Cars used to ship it are used only for carbon black, and when shipped in non-specialised cars, that material usually contaminates the car to a degree that the car is not useable for any other commodity.

Wayne