Question

what do we observe when ammonia is brought in contact of hydrogen chloride gas

Answer 1

A white solid fume of NH4CL is obtained.
It can be a test for th presence of ammonia.
NH3 (g) + HCl (g) ->NH4CL (s)
hope it helps.:)

Answer 2

Concentrated ammonia solution is placed on a pad in one end of a tube and concentrated hydrochloric acid on a pad at the other. After about a minute the gases diffuse far enough to meet and a ring of solid ammonium chloride is formed.