Interesting contrast in tank car photos

I check the John W. Barriger III National Railroad Library flickr site at least once per week to see if anything new has been posted. I recently noticed two photos that I thought provide a nice contrast. The first photo, of Mexican Petroleum (MPLX) 356 is an American Car & Foundry Type 17 10,000 gallon tank car, built in January, 1919. It incorporated the details typical of the AC&F Type 17, notably the underframe. The other important details for a Type 17 include the double rows of 'staggered' rivets where the radially oriented tank sheets over and underlap each other and the tank relief valves mounted on an 'elbow' attached to the side of the expansion dome.

Kanotex Refining (KOTX) 8108 presents an interesting contrast. While built in December, 1918, one month prior to MPLX 356 shown above, it has a 'modern' tank with longitudinally oriented tank sheets. It is also unusual in that most cars with longitudinally oriented tank sheets had tank relief valves mounted on top of the expansion dome, adjacent to the manway.

Lastly, I include a third photo to provide a counterpoint to complete the story. From March, 1920 is Transcontinental Oil (Marathon) TROX 1511, which displayed the 'complete' transition to a 'modern' car with longitudinally oriented tank sheets, relief valves on top of the expansion dome, and a safety manway. There are examples of AC&F tank cars with this arrangement of details from as early as 1919, including White Oil (WHOX) 1185, but that car had a white tank, making viewing of the details in the photo significantly more difficult.

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