TANK CAR APPLICATIONS

There should be one dome for each compartment in the tank. The dome is the expansion space for the commodity being shipped.  There was a six dome wine car that use to run around this area.  Tank cars have better safety records than tank trucks, so dangerous commodities usually travel by rail. Tank cars are usually leased cars to avoid cleaning between every load and, as you pointed out, many products need special interiors.  Different loads also have different density, so heavy commodities go in small cars and light commodities go in large cars.  My favorite tank car were the ones that used to ship tetraethyl lead, the old gas additive. Very heavy commodity very small cars.  

There are so many different things shipped in tank cars you will just have to pick one.  You could do a soft drink factory and get corn syrup and CO2 by tank car and ship out finished product by boxcar.

The chemical you were referring to in your chemistry class was probably hydrofloric acid, used to etch glass.  It was used in a refinery I worked in to treat oils.  It did arrive in tank cars.  I think it traveled in plain steel cars as steel is one of the things it did not eat.   I never worked in the HF plant and was glad for it.

Thanks, Mr. Johston:  I was mulling hydrochloric acid around in my mind, H2SO4, when I hit  "post" , and then, too late, remembered hydroflouric acid, not thought of

for years.  Models of six dome wine cars have been made for years...didn't Third Rail

do one, and one of the old O scale kit builders, and several in HO?  I have seen brass small tank cars in HO and I think in O, lettered maybe for "Ethyl".  I  think I have seen full size three rail cars for "Ethyl Corp.", but, not ANY small tank cars in three rail, but?  The 8000gal question was my biggie, as I wanted the car correct for

the period.  Six dome wine cars are like butter dish milk cars....I like 'em but I don't

think they were ever seen in the area I model.  I have suspected the butter dish cars

were confined to the northeast, and the wine cars to Northern California, but, vaguely,

have I seen a wine car for upper NY state?

Believe the dome was to mount a manhole entry for cleaning and repair of the tank car.

I don't know about old tank cars from the 1950s, but on modern tanks, the dome is where all the valves are maintained and protected. The valve platform can be unbolted to  allow access inside for cleaning and maintenance. 

Cleaning the inside of a tank car is considered a "confined space" hazard. If a worker goes inside he would need full respiratory protection with supplied air. 

Cleaning is usually done with steam. If a freshly cleaned tank is then sealed up without an open vent, as the hot tank cools it can actually implode. 

youtube search railroad tank car implosion  

The older tank cars are the same way with the valve handle for the bottom discharge valve inside the dome.  Also the dome is where the safety relief and rupture discs are usually located.  I have been inside tank cars, but not something I would ever want to do again.  In addition to steam, we used something called a Butterworth nozzel to wash the interior with caustic soda.

The tank size is tied to the density of the comidity and the capacity of the trucks.  An old 8000 gallon was probably carrying oil on 4 1/4 X 8 journals.  These would have been replaced by 10000 gallon cars on 5X9 journals. That change probably took place 1910 to maybe 1920. There are people on this board who know more about tank cars than I do. Hopefully they will provide better information.

Propane and Propylene tank cars [LPG] have no bottom valves with all valves mounted in  dome. These cars have a design pressure of at least 180 psig, and are fitted with a safety relief devise also located in the dome. The liquid emptying valve has a dip tube which goes down close to the bottom of the tank. There are also vapor return valves located in the dome. These cares are either emptied by using a pump or the preferred method using a compressor.