Tony, I'm sure I've seen official SP documents somewhere that used
the term hog fuel, but I just looked up SP 52490, a rebuilt A-50-6
(de-roofed with added small side-doors) and it is listed in the 1955
ORER simply as a "wood chip" car. I have a 1956 photo of 52490 and
it's loaded with can only be hogged fuel -- shredded bits of wood.
It looks like the stuff people put around their trees and flower beds.
I also have a 1957 shot of MILW 273221, a rebuilt 50 foot single sheathed
box car. This one has a roof with numerous hatches, no main doors, and
a line of dump doors along the bottom of the sides. MILW had hundreds
of these puppies in 1959!! They are also listed as "wood chip" cars.
Sigh. I wish Martin and Al had been more interested in the 1950's to
early 60's. So MANY interesting rebuilds back then!
No argument with this as far as it goes, but wood chipper
machines for decades in sawmills have been called "hogs" and their
product "hog fuel." They are by means restricted to bark, and the
cargo carried in SP "hog fuel" cars was certainly not all bark. This
goes back to the days that much hog fuel was burned in conical
structures at sawmills when it could not be sold.