Have you seen the ammonia fountain?

Yasmin Jayathirtha

Many months ago, October 2012, to be exact, I had covered the reactions of nitrogen in the laboratory. Under Ammonia, the properties were described as; ‘ammonia has a pungent smell, is a base and very soluble in water.’ A spectacular way of showing the solubility is to do the fountain experiment. It does not always work, so do try it out before demonstrating it.

The figure shows a complicated arrangement with tubes and connections with a U-tube for drying the gas. It is rather difficult to set up, since one has to collect many stoppers and tubes and make sure it is air-tight. This can be cumbersome and though I enjoy showing spectacular experiments, I rarely demonstrate this one.

Last month, a group of students wanted to try it out. As I helped them search for the materials needed, looking for a U-tube and stoppers that would fit and glass tubes to go into the stoppers, a bright idea struck me. Why bother with this elaborate setup? Just the previous week, to make ethene by dehydration of ethanol, we had passed the ethanol vapours over the catalyst placed in the boiling tube itself. It was a very self-contained unit. Why not put the drying agent in the boiling tube itself? After all, the drying agent (calcium oxide) was also one of the reagents, so any mixing would not be a problem. Finally, this was what was done. Two large spatulas each of ammonium chloride and calcium oxide were ground together and put into a boiling tube. Two or three spatulas of calcium oxide was layered on top and set up. The mixture was heated and the gas collected in a flask as shown in the photographs. The tube, from which the fountain spurts out, is a piece of a broken pipette and has a narrow tip. Dip the tip in water and stopper the flask. As the water dissolves some of the ammonia, the pressure inside decreases and the water from the beaker is sucked up. We had put phenolpthalien in the water, so the water changed from colourless to pink. This is a much simpler way of setting up the experiment, so those of you who had been intimidated by the idea of getting U-tubes and other material, please do try this out.

The author works with Centre for Learning, Bengaluru. She can be reached at yasmin.cfl@gmail.com.