Figure shows an experimental set up for the laboratory preparation of pungent smelling gas. The gas is alkaline in nature.
How will you find that the jar is full of gas?
When a moist red litmus paper placed just at the mouth of the gas jar turns blue
A glass rod dipped in concentrated hydrochloric acid just below the mouth of the gas jar is not preferred as the dense white fumes formed would enter the gas jar and hence adulterate the contents of the gas jar.