One summer, I occupied myself as a lowly laborer in an Estherville, Iowa Morrell meat packing plant. Along with my fellow seasonal workers ("the PhDs". By serendipity, all of us were in grad schools during the year), one of our recurring jobs was to unload the salt cars that would periodically arrive at the plant, the salt needed for keeping the fresh hides from spoiling before they could be tanned.
Estherville was on the Rock Island, and the salt always arrived in intact but ancient dedicated single sheathed boxcars originating in Kansas. To minimize demurrage, we were ordered to empty the car right away, which always involved overtime- which was OK for us. The salt was loose in the car, and we used coal scoops and wheel barrows to transport the salt to a hopper that opened into the hide cellar under the main plant kill floor.
It was hotter than hades outside, and worse in the close confines of the boxcar. The salt would get into and under your clothes- a totally unpleasant job. One of us would "stand lookout" while slumping guzzling a bottle of Pepsi ("5 cents"), while the others toiled, and after a period, it would be the next person's turn, etc. The periodic resting was good for both survival and the wallet.
As to ATSF cars in salt service off-line, I believe that on this list several years ago was a photo of an ATSF ice reefer in Iowa that listers decided that in all probability was in salt service.
Denny S. Anspach MD