What was found
BOS - FLT 1835 - EN ROUTE BOS-DFW, AFTER TAKEOFF A HOT MISTY ODOR WAS PRESENT IN COCKPIT FOLLOWED BY FLIGHT ATTENDANTS REPORTING SMOKE FILLING THE CABIN, SOME IN COCKPIT, FLIGHT ATTENDANTS REPORTED SMOKE WAS ORIGINATING AROUND ROWS 17 AND 18. DECLARED EMERGENCY, RETURNED TO TO BOS AND LANDED WITHOUT INCIDENT. SMOKE DISSIPATED DURING DESCENT AND LANDING. TAXI TO GATE WAS UNEVENTFUL. REPLACED APU O-RING AT MAGNETIC DRAIN PLUG. REPLACED LEFT COALESCERS BAG. ACCOMPLISHED PACK BURN OUT. SYSTEM GROUND CHECKED NORMAL OPERATION. (M)