Hmm, lots of misconceptions here. Memphisbelle, take the bottle outside and cover the crystals with either neat or brown vinegar. The gas given off will be carbon dioxide and it may seem a vigorous reaction depending on the amount of crystals present, but it will get the job done.
Peter Pedant, for well over a century, smelling salts have been made from ammonium carbonate with sometimes small traces of ammonium bicarbonate present. In years gone by this was known as salt of hartshorn, derived from the more familiar spirits of hartshorn.
Ammonium Chloride or sal ammoniac never really took off in smelling salts as it was invariably mixed with ammonium hydroxide solution, which gave it the ammonia smell. As Ianfiat has pointed out, ammonium chloride is odourless.
Graham-W, although spontaneous decomposition of ammonium carbonate is known, it does not necessarily happen in all cases. The decomposition is influenced by the degree of exposure to air.