I could be completely wrong here, but although pressure treatment is done that way, I wasn't under the impression that creosoted ties were produced this way, especially back in the early 20th century. I'll have to do some research on this one as it's an interesting question.
Mike
Edit: I was obviously wrong. Not the first time and probably not the last. Here's an interesting article on tie treatment and date nails. I didn't realize that pressure treatment of ties dated back to the early 19th century. It seems that I learn something new everyday and that's a good thing. Here's the link for the article. http://facstaff.uindy.edu/~ oaks/Articles/History.pdf It's in pdf format for easy printing and reading at your leasure.
Creosoted ties are from the very distant past. Maybe a bit more modern but still from the past; Chromated copper arsenate (CCA) using a vacuum/pressure wood treatment system.
Sawmills with a large output sometimes had a rail system complete with a small rail mounted locomotive or rail tractor while smaller operators just used their forklift or rubber tyred tractor crane to shunt the wagons into and out of the wood treatment cylinder.
The size of the rail system again depended on the size of the operation. If the sawmill processed long timbers such as electricity poles or wharf piles, than the rail wagons and rail tracks used to load the timber into the pressure cylinder would be more extensive than that used by operators who processed shorter and smaller wood products.
In a similar manner, the pressure cylinder size depended on the operators’ needs, as did the rail track size and gauge.