Preparation of Ammonium Hydroxide
Ammonium hydroxide is prepared by saturating water with gaseous ammonia. Ammonia gas is generated and conducted directly from the flask without the introduction of a drying tube into an empty gas washing-bottle which serves to collect any solid particles mechanically carried over.
Gaseous ammonia is prepared by gently heating crude ammonium chloride (or ammonium sulfate) with dry calcium hydroxide:
Powdered ammonium chloride and calcium hydroxide in equal quantities are placed in Erlenmeyer flask fitted with a glass elbow. On the application of gentle heat ammonia is rapidly evolved. The gas is then conducted through a series of three 3-necked Wolff bottles of 300-400 ml capacity, each half filled with distilled water. Each Wolff bottle is fitted with an elbow reaching to the bottom of the bottle, a vertical safety-tube dipping just beneath the surface of the water, and an elbow extending just below the cork.
As soon as all the air is driven out of the generating flask, the bubbles rising through the water in the first of the series of Wolff bottles grow smaller, and finally all the gas is absorbed. As soon as the water in this bottle becomes nearly saturated the gas rises through the solution unabsorbed and passes through the elbow into the second bottle, etc. As the ammonium hydroxide is lighter than water, it is important that the glass elbows extend to the bottom of each bottle, as otherwise the upper surface of the liquid would become saturated, while the lower strata would be but slightly alkaline.
Chemical lecture experiments, by F. G. Benedict, 196-197, 1916.