The NH cars were 41' drop-bottom gondolas.
Any idea where the sand was shipped from? I highly doubt it was loaded on the NH. There are no loads of sand shipping from CT in the 1950-1954 1% waybill study, although that doesn't mean that none at all shipped since that was only 1%. I don't have the data for RI or MA, so maybe from there. But that seems like a long trip for something like sand.
Modeling the New Haven Railroad 1946-1954