From a slide on eBay, this appears to be a Tide Water tank car, TWOX
3050, that has been converted from a three compartment into a single
compartment based upon the flanges on the top of the tank. There is no
date when the slide was taken.

Bob Witt

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=380166651780&ssPageNa\
me=STRK:MEWAX:IT