There was a full article on these cars in TIES magazine a few years ago. Someone needs to help find which issue.
It has always been unusual for any railroad to own revenue tank cars. There were two groups of 100T capy cars blt by ACF and GATX, painted Southern freight car brown. They were in captive service between Rockland, FL and Vertagreen, near Sheffield, AL. (Rockland was east of Mulberry, FL off SR 60). I lived in Sarasota and Brandon at the time so I was able to photograph them parked beside the highway quite often.
The attached photo of Sou 323 was taken at Chattanooga 8-93 long after the Vertagreen service ended. They could not be used to ship flammable materials (like diesel fuel) so they were used to store used oil at Citico (and probably other shops).
Back in the mid-60s Southern routinely handled several tank cars of Vertagreen liquid fertilizer on the rear of Nos 7 & 8, the KC-Florida Special, between Brunswick GA and Birmingham AL. Does anyone know the history of these cars, more specifically the points of origin and destination?