Ammonia gas is normally dried with?

A drying agent must absorb water without reacting with the gas. Ammonia is a basic gas.

Quicklime (calcium oxide) is a basic drying agent. It takes up water but does not react with ammonia, so it is used.

Concentrated sulphuric acid reacts with ammonia to form ammonium sulphate. Anhydrous calcium chloride also reacts, forming a compound with ammonia (CaCl₂.8NH₃). Magnesium sulphate is not an effective drying agent for gases.