45-49] EXPERIMENTS ON AIR 19 



45. One of the most striking properties of ammonia gas 

 is its extreme solubility in water. Place a ground-glass plate 

 over the mouth of a jar filled with the gas as in the last 

 experiment. Then hold the jar so that its mouth dips under 

 the surface of the water contained in an earthenware dish. 

 Remove the glass plate. The water will rush up into the jar. 



46. Another property of ammonia is its action on tur- 

 meric paper, which it turns brown. Take a few drops of 

 strong ammonia in a test-tube. Moisten a strip of turmeric 

 paper and hold it over the mouth of the test-tube. It will 

 probably become brown at once from the ammonia which 

 escapes from the solution. If it does not alter its colour 

 warm the liquid slightly ; the paper will immediately be- 

 come dark brown. 



EXPERIMENTS ON AIR 



47. Of the minor constituents of the atmosphere (29) 

 carbon dioxide and water-vapour may be readily detected, 

 but the presence of nitric acid and ammonia are less readily 

 shown. Methods for detecting carbon dioxide and water - 

 vapour in air are described below. 



48. Carbon Dioxide in Air.— Pour a little clear 

 lime-water into a saucer or shallow evaporating-basin and 

 allow it to stand for an hour. At the end of that time it 

 will be covered by a thin film of carbonate of lime or chalk. 

 This is produced by the action of carbon dioxide, as ex- 

 plained in paragraph 42, and shows the presence of that 

 gas in the air. 



49. Water-vapour in Air.— Place on a dry porce- 

 lain tile a few lumps of dry calcium chloride and allow 

 them to stand for an hour. At the end of that time the 

 lumps will have become quite wet. The moisture which 

 has been thus attracted can only have come from the air. 

 This experiment, therefore, shows that the air contains 



water-vapour. 



c 2 



