What was found
UPON DEPARTURE FROM THE AIRFIELD AT 0133, AT 500' AGL, 70 KIAS, AND 8.5 FLI WITH THE DEMIST ON, SMOKE BEGAN FILLING THE COCKPIT ORIGINATING FROM THE DEMIST NOZZLES. CREW OPENED THE SLIDING WINDOWS TO VENT THE COCKPIT, DEMIST WAS SHUT OFF, AND THE AIRCRAFT WAS RETURNED TO BASE WITHOUT FURTHER INCIDENT. WHEN THE AIRCRAFT WAS ON THE GROUND AT "FLY" DEMIST WAS TURNED BACK ON AND LIGHT SMOKE BEGAN COMING OUT OF THE NOZZLES. DEMIST WAS SHUT OFF AND THE AIRCRAFT WAS SHUT DOWN.