A bottle of ammonia and a bottle of dry hydrogen chloride connected through a long tube are opened simultaneously at both ends, the while ammonium chloride ring first formed will be:

ammonium chloride ring first formed will be Near the hydrogen chloride bottle. Because HCl diffuse slowly compound to $N{H}_3$ . NH₃ being lighter diffuses faster and reacts with HCl to form ammonium chloride creating a white fume.