This model dates to the early days of N scale (late 60's / early 70's). It was originally imported as part of the Aurora "Postage Stamp" line, and later on by Minitrix / Model Power (up until about 1980).
This is a surprisingly accurate model of an ACF prototype built in the 40s and 50s. These cars were used for carrying small containers of Acrylonitrile. The containers were loaded through the sides (through the triangular frame section) and fastened by steel rods. The cars are listed in the "Official Railway Equipment Register" 1977, page 959 as SHPX series 50020. Acrylonitrile is highly flammable, toxic and prone to explosive polymerization - hence the need for small, specialized containers.
Not the same prototype, but it shows how cars of this type are loaded -
