192 OXYGEN. 



simple state ;"* this might have been said with still greater truth, of 

 carbon and hydrogen. 



Remarks. 



Oxygen unites with every simple body, but it has neither acid nor 

 alkaline properties. It is the agent in all common cases of combus- 

 tion, which in most instances, is nothing more than rapid oxidation, 

 with the emission of heat and light ; and a slow combination of ox- 

 ygen often goes on without either ; common iron rust is produced in 

 that manner. 



Combustion and respiration have the same effect in vitiating the 

 air ; the air in which an animal has died, will not support combus- 

 tion, and the air in which a combustible will not burn, will not sup- 

 port animal life. 



Oxygen is involved in the chemical study of all bodies, simple 

 and compound. The term oxygen means strictly the ponderable 

 part of oxygen gas ; the material part is known only in combination ; 

 it has never yet been isolated so as to exhibit it separately ; in its 

 gaseous form, it is combined with caloric and light, and probably 

 with electricity. 



It appears to exist no where in nature, in a pure and disengaged 

 state, and we always obtain it for use by evolving it from one of its 

 combinations. Healthy leaves of vegetables, acted upon by the di- 

 rect sun beams, throw it off incessantly into the atmosphere, and it 

 is supposed to be a principal means of recruiting the waste of oxygen 

 which arises from combustion, respiration, and other natural processes. 

 In the dark, a different gas, the carbonic acid is said to be disengag- 

 ed ; the subject will be resumed in giving the history of that gas. 



It is fortunate that oxygen gas can be easily and abundantly ob- 

 tained from the native oxide of manganese, as there is scarcely any 

 other from which it could be obtained at all, and no other which 

 could supply the demands of chemistry and the arts. 



Nitre is perhaps the easiest resource for affording oxygen gas, but 

 only the early portions are pure ; a little may be heated to low red- 

 ness in a gun barrel, but we should avoid the mouth, as the melted 

 nitre is apt to boil up, congeal above the ignited portion of the tube, 

 and thus acting like a wad, by and by, after a cessation, the gas causes 

 an explosion, by which the hot nitre is driven about. Every thing 

 connected with the history of oxygen, is elegant, beautiful, and in- 

 structive ; without it there would be no beginning of animal life, nor 

 any adequate means of producing and regulating heat. 



* Murray, Vol. I, p. 407. 



