134 ATMOSPHERIC AIR. 



the proportion of 21 of the former and 79 of the latter. It 

 contains also about one part in every thousand of carbonic 

 acid gas, a considerable portion of water in a state of elastic 

 Fapour, and several adventitious substances. 



Oxygen is an element or simple substance generally dif- 

 fused through nature, though like caloric it does not exist 

 by itself. It takes its name from two Greek words, signify- 

 ing that which produces or generates acids, because one of 

 its general properties is to form acids by combining with dif- 

 ferent substances, which are called the bases of the several 

 acids. Its different combinations are essential to animal 

 life and combustion. Acted upon, or combined with caloric, 

 it becomes oxygen gas, which is distinguished from all other 

 gaseous matter by several important properties. Inflamma- 

 ble substances burn in it under the same circumstances as 

 in common air, but with infinitely greater vividness. If a 

 taper, the flame of which has been extinguished, the wick 

 only remaining ignited, be plunged into a bottle filled with 

 it, the flame will instantly be re-kindled, and will be very 

 brilliant, and accompanied by a crackling noise. If a steel 

 wire, or thin file, having a sharp point, armed with a bit of 

 wood in a state of inflammation, be introduced into a jar 

 filled with the gas, the steel will take fire, and its combus- 

 tion will continue, producing a most brilliant phenomenon. 

 Oxygen gas is a little heavier than atmospheric air, and from 

 its being absolutely necessary to the support of animal life, 

 it has been called vital air. 



Nitrogen is a substance diffused through nature, and par- 

 ticularly in animal bodies. It is not to be found in a solid 

 or liquid state ; but combined with caloric, it forms nitrogen, 

 or azotic gas, in which no animal can breathe, or any com- 

 bustible burn. It is uninflammable and somewhat lighter 

 than atmospheric air, and though, by itself, it is so noxious to 

 animals, it answers an important end when mixed with oxy- 

 gen gas in atmospheric air. Were it not for this large quan- 

 tity of nitrogen in the atmosphere, the stimulating power 

 of the oxygen would cause the blood to flo'V with too great 

 rapidity through the vessels; the consequence of which 

 would be, that the life of man would not be protracted to 

 the length that it now is. The vermilion colour of the blood 

 is owing to the inhalation of oxygen gas. When the dark 

 purple blood of the veins arrives at the lungs, it imbibes the 



