… before hoppers made it easy.
“Before covered hoppers, grain used to move primarily by boxcar, and devices like these were sometimes employed to tip the grain out of the car.”
Steve,
Somebody spent a lot of time coming up with that design, and expensive too. i always thought they used a big vacuum hose to convey / suck the grain out.
Even the narrow gauge D&RGW had a rotary dumper back in the 30’s.
Very cool photo that somebody thought too take …even in black and white it appears everything is quite clean and new.
I wonder if that Rube Goldberg contraption shook the boxcar, or just lifted one end until the grain ran out? The visible rigging seems kind of flimsy to me, but what do I know, I still play with trains. 
Steve,
That is a most useful and highly interesting pic posted by you. I am slowly gaining very small areas of real estate near my ROW. My wife spends a little less time in the garden now and has relinquished a couple of areas which I can make use of.
I am contemplating adding very small lineside facilities into the vacant plots but as the areas available are small so will, of necessity, be the structures. As I have twelve coal hoppers a coal facility would be a good candidate. Also nine gondolas and seven boxcars are on hand.
There seems plenty of other options: saw mill, logging loader, grain elevators and so on but so many that I have seen in photographs are too large and elaborate for my locations.
Your pic seems to show that smaller facilities for loading and unloading various commodities did exist. I know most large scalers have many boxcars but maybe fewer covered hoppers so it seems a grain unloading operation can be done without hoppers but just boxcars.
It is info and pics such as this that is invaluable to modelers like my self that do not know a great deal about the American railroads of yesteryear.
I believe it was rocked up and down lengthwise, slowly as the grain poured out the door.
Shaking it would allow parts of the box car to be unloaded as well. 
When grain was shipped most places did not have this type system. Some places I recall had vacs others removed the temporary grain door and then shoveled the grain out. man what a job. Later RJD
Of interest RJ to where was the grain shoveled?
Those were the days when men worked physically hard and burned off all the calories acquired by eating large rib sticking meals.
It seems that many still eat the same quantities but -my oh! my, the calories don’t get to go away. lol