(adds injuries, details) CHICAGO, Dec 4 (Reuters) - Two locomotives and 21 cars of a Union Pacific <UNP.N> railroad freight train derailed in southern Illinois on Monday, spilling a chemical that forced the evacuation of about 75 homes in bitterly cold weather, the railroad said. Spokesman James Barnes said several people were taken to a hospital for checks after they reported breathing problems but the substance which leaked was an industrial detergent that may cause irritation but is not volatile. Crews were in the process of removing some of the cars which left the tracks, he added, and the cause of the accident was still under investigation. Some of those forced to leave their homes after the accident were taken to a nearby church. The 83-car train was headed to Chicago from Houston when it left the tracks near Benton, Illinois, around 2:35 a.m. (3:35 a.m. EST/0835 GMT), he said.
