Air 223 



5. Suggest reasons for 



(a) The extinction of a candle after it has burnt for a short 

 time in a closed gas-jar. 



(6) Phosphorus burning readily in air which will no longer 

 support the combustion of a candle. 



6. Why does opening a window sometimes cure a smoky fire? 



CHAPTER XIV 



MINOR CONSTITUENTS OF AIR 



151. In the last chapter, the two chief constituents 

 of air, oxygen and nitrogen, were dealt with, and these 

 two make up together about 97-6 per cent, by volume 

 of our atmosphere. Argon, the gas formerly measured 

 with the nitrogen, amounts to about 0-9 per cent., 

 leaving 1-5 per cent, to be accounted for. The bulk of 

 this remainder consists of two substances, and our next 

 business is to find out what they are. 



EXPERIMENT 87. Burn a candle in a dry clean gas- 

 jar as in Experiment 77. Notice that during the 

 burning the sides of the jar become moist. This 

 moisture, if sufficient be obtained, may be shown by 

 suitable tests (v. Chapter xvn) to be water. When the 

 candle has gone out, remove it, and pour a little clear 

 lime-water into the jar. Cover the mouth of the jar 

 with a glass plate, and shake the jar vigorously. The 

 clear lime-water becomes turbid, and if allowed to 

 stand, a fine white powder settles on the bottom of the 

 jar. Shake up some lime-water in a jar of ordinary air. 

 No perceptible turbidity will be produced. We have 

 thus obtained evidence of a second product of combus- 

 tion of the candle. It is an invisible gas, like air, 



