http://www.railcarphotos.com/PhotoDetails.php?PhotoID=44029
As it says on the web page you are linking to, right under the picture, it is a “bottle car”.
A quick search on http://www.google.com for search terms “bottle car” and “railroad” yields e.g. this explanation:
http://en.wikipedia.org/wiki/Tank_car#Torpedo_cars
I am sure there are people around here than can tell you more about torpedo cars/bottle cars than you ever wanted to know 
Smile,
Stein
A carrier for molten metal, it would seem. Mentioned, as I recall, in the W&LE issue of Trains recently. Bottle car.
it is a bottle/torpedo car… it is used in steel mills to take molten iron from the furnes to other prosses in the mill to turn it into steel…
csx engineer
Also called a torpedo car. They are spotted under the blast furnace casthouse floor which has refractory lined channels about 2’ wide and 2’ deep that the molten metal flows in to the cars. As statedthey are used for moving the molten iron to either a BOF, electric furnace or open herath for refining into steel. That picture is a fairly modern one since it has siz wheel buckeye trucks on it. Since FRA rules say an axle can handle upto 80,000# that would limit the car to about 800,000# or 40 tons of iron. I am not sure if it is physically possible to contain that much but that would be the limit. I have seen situations where a problem has developed at the balst furnace where the iron can not be redirected when a car is full so the iron just flows onto the ground. It is generally standard practice to have an idler car or two and an engine hooked to the car in case of such a situation so the car can be pulled before the iron sets up freezing it in place. When one passes you in a steel mill you can be as close as three feet to one. Many a time I wondered if there would still be paint on that side of my car after I got away from it. The heat from one with worn out refractory is extremely hot even with the windows up in a car. At the melt shop the car is rotated to pour the iron into a ladle for insertion into the melt furnace. Each car has a geared drive in the end that tilts the center portion and pour the iron out through the top hole. These drives are always electrically drivven and the operator hooks up a 440 volt connector to the car to provide power.
…Do you really mean 40 tons…?
Assuming that the axle size and bearings are correct (all axles are not created equal; rail load depends on bearing size). More likely, this car could handle a gross rail load of about 326 tons, not 400. Now that’s the gross rail load–you have to take the weight of the car itself away from that to determine the load limit. These cars are in very limited service, so UMLER (in which one could usually find out about dimensions and capacity) doesn’t show these cars. It appears that load limit and light weight may be stencilled on the car; the photo doesn’t allow us to read them, though.
Depends on what you mean by “modern”–note that the six-axle trucks have been modified from friction-bearing trucks, with journal-box covers.
This photo is of one of the cars that used to serve the Interlake Steel (later Acme, now Mittal?) mill in Riverdale, Illinois. The trains (with anywhere from three to five of these cars, spaced apart by idler gons) would pass through Dolton in both directions. If the cars were loads, one could definitely feel the heat–and see the glow, after dark or on a cloudy day.
Thanks for the info…[bow]