VI.] THE ATMOSPHERE. 79 



mercury had taken oxygen from the air, and combined 

 with it to form the red oxide, from which, by stronger 

 heating, the oxygen gas could easily be recovered in a 

 state of purity. It remained, however, to inquire what 

 was the character of the air left in the vessel which had 

 been thus robbed of its oxygen. On plunging a taper 

 into the residual air it was at once extinguished; and on 

 introducing a living animal into the air, the creature was 

 suffocated. The latter property suggested to Lavoisier the 

 propriety of giving to this foul kind of air the name of 

 Azote ;^ — a name which it still retains in France, but which 

 has been superseded elsewhere by the term Nitrogen? 



On accurately examining a given measure of atmospheric 

 air, it was found that it contained about one-fifth its bulk of 

 the gas oxygen and four-fifths of nitrogen. To speak with 

 more accuracy, loo volumes of pure air contain 20-8 vols. 

 of oxygen and 79-2 vols, of nitrogen. If instead of a 

 given volume, or measure, a given weight of air is examined, 

 it will be found that 100 parts by weight — whether grains, 

 ounces, or pounds — contain 23 of these parts of oxygen 

 and 77 of nitrogen. 



Before proceeding to examine more closely into the 

 composition of atmospheric air it may be well to note 

 the characters of the two constituents into which it has 

 just been seen that air may be resolved. In most of the 

 chemical phenomena in which atmospheric air takes part 

 it is the oxygen which is the active agent. It has been 

 shown that a glowing taper bursts into flame when plunged 

 into oxygen. In like manner sulphur, phosphorus, charcoal, 

 even iron-wire, will burn with great vigour in this gas; 



' Azote, from the Greek privative d, and ^wtj, zoe, life. 

 2 Nitrogen, from nitre, in consequence of nitrogen being a constituent 

 of the salt called nitre or saltpetre. 



