CHAPTER XIV. 



NITROGEN, THE AIR, AMMONIA AND NITRIC ACID. 



THE air, an invisible, tasteless, odorless gas surrounds us every- 

 where. In motion it is wind, from which we may recognize not 

 only the existence of the air but something of its power as well. 

 It has weight, as shown by the action of the common pump and 

 mercurial barometer. 



The air contains oxygen as shown by the fact that the same 

 products arise from burning sulphur, carbon and other sub- 

 stances in the air, that arise from burning those substances in 

 oxygen. But combustion in the air is not as prompt and vig- 

 orous as it is in oxygen, so that the oxygen of the air seems to be in 

 a sense diluted. On a broad piece of cork, or bit of board, fasten a 

 porcelain, crucible or a piece of earthenware; place it on the surface 

 of water; put on the porcelain a piece of phosphorus about the 

 size of a pea and set fire to it, then invert a jar over the burning 

 phosphorus, at first the heat of combustion may drive out a 

 few bubbles of air, but soon the water will rise in the jar, taking 

 the place of oxygen used in the combustion. The white clouds 

 which fill the jar at first is oxide of phosphorus, which the 

 water at length absorbs, and a transparent, tasteless, odorless 

 gas remains, but does not fill the jar. If we measure the jar 

 carefully it will be found that water occupies about one-fifth of 

 its capacity, the gas occupying the balance. 



This gas is called Nitrogen, its symbol is N, and its combining 

 weight 14. If an experiment is carefully performed it will show 

 that the air is composed of about 21 per cent, of oxygen to 79 

 per cent, of nitrogen. Close the jar and invert it, then lower into 

 it a lighted candle and it is extinguished. Confine in it a mouse 

 or a bird and it dies ; the gas will not support combustion, it will 

 not support life. Nitrogen is prepared in quantity by passing 



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