Dutch Vessel belonged to the American Petroleum Company. ROTTERDAM, Feb. 23. The Dutch tank steamship La Flandre, belonging to the American Petroleum Com-pany, sank on her voyage from New York to this port. The Second Engineer and a seaman have reached here on board a British steamer, The steamship La Flandre was of 2,047 tons gross, 270 feet long, and 37 feet beam.  She was built in 1888 at New-castle-on-Tyne.