The PRR provided cast iron "loading instruction" plates on the sides
of their covered hoppers up to 1953 (stamped plates there after). In my den
I have one such plate off a class H33 covered hopper (built 4/53).
The commodities listed on it are: Pulverized coal, soda ash light, soda
ash dense, hydraulic lime, cement, sand dry, sodium nitrate, feldspar, and
dolomite. The first five listed items were to be loaded fully, while the
later ones had specified distances from the hatch at which to stop loading.
My experience was that all PRR covered hoppers into the mid-1950's loaded
only mineral loads. I think the loading of food stuffs into covered hoppers
was facilitated by the introduction of modern linings for the cars which
could be cleaned and sanitized.