STUDY OF THE ACTIVE PART OF THE AIR 133 



will no longer allow a candle or taper to burn in it. This is one reason 

 why it is called the inactive part of air. The name by which this gas 

 is known to chemists is nitrogen. 



Properties of nitrogen. The gas nitrogen is very inert, since it can be 

 made only with difficulty to combine with any other substance. It does 

 not burn, nor will it allow other substances to burn in it ; or, as usually 

 expressed, it does not support combustion. A mouse dies if put into this gas. 



If the negative nature of the properties of nitrogen is borne in mind 

 and is considered in connection with the very active powers of oxygen, 

 it will be understood that its presence in the air serves the purpose of 

 diluting the oxygen, weakening its powers, and making combustion- 

 much less intense than it would otherwise be. 



If nitrogen obtained from air be heated with either magnesium or 

 lithium, it is found that nearly 1 per cent, of it remains unabsorbed. 

 This residue is another substance present in the atmosphere to the 

 extent indicated, and called argon. Argon is also very inert, more so 

 even than nitrogen. Owing to this, even until the year 1894, its 

 presence in the air had been completely overlooked, although, nearly 

 a century before, the eminent chemist Cavendish had unknowingly 

 obtained some, regarding it as an impurity which he had overlooked 

 an example of the importance of giving attention to the minutest details 

 in scientific investigations. After the discovery of argon, four other 

 new gases helium, neon, krypton, and xenon were found to be 

 permanent constituents of air, but they occur in such minute quantities 

 that their presence need only be mentioned here. 



Chemical composition of air. What may be termed the funda- 

 mental gases in air are oxygen and nitrogen. Argon and the four 

 other new gases may for our purposes be regarded as part of the nitrogen. 

 Carbon dioxide and water vapour are practically always present, 

 and various other gases or vapours frequently occur in small quantities ; 

 but these may be regarded as impurities, and ought not to be considered 

 as constituents of pure air. The following table shows the percentage 

 composition of air as regards volume ; that is, for instance, the number 

 of cubic feet of the various gases present in 100 cubic ieet of the 

 atmosphere : 



Oxygen, a gas which supports combustion, - 2 TOO 



Nitrogen, an inert gas, 78*03 



Argon, an inert gas, 0-94 



Carbon dioxide, a suffocating gas, - - 0'03 



Water vapour, ------- Variable 



Nitric acid, "j 



Ammonia, i . . . . . traces 



Ozone, 



