282 NITROGEN. 



compound, which is absorbed and decomposed by the acid. 

 Of the odoriferous principles of plants, the miasmata of marshes 

 and other matters of contagion, the presence, although suf- 

 ficiently obvious to the sense of smell, or by their effects upon 

 the human constitution, cannot be detected by chemical tests. 

 But it may be remarked in regard to them, that few or 

 none of the compound volatile bodies we perceive entering 

 the atmosphere, could long escape destruction from oxidation. 

 The atmosphere contains indeed within itself the means of 

 its own purification, and slowly but certainly converts all 

 organic substances exposed to it into simpler forms of matter, 

 such as water, carbonic acid, nitric acid and ammonia. Al- 

 though the occasional presence of matters of contagion in 

 the atmosphere is not to be disputed, still it is an assumption 

 without evidence, that these substances are volatile or truly 

 vaporous. Other matters of infection with which we can 

 compare them, such as the matter of cow-pox, may be dried 

 in the air, and are not in the least degree volatile. Indeed 

 volatility of a body implies a certain simplicity of constitution 

 and limit to the number of atoms in its integrant particle, 

 which true organic bodies appear not to possess. It is more 

 probable that matters of contagion are highly organized par- 

 ticles of fixed matter, which may find its way into the at- 

 mosphere, notwithstanding, like the pollen of flowers, and remain 

 for a time suspended in it; a condition which is consistent 

 with the admitted difficulty of reaching and destroying those 

 bodies by gaseous chlorine, and with the washing of walls 

 and floors as an ordinary disinfecting practice. On this obscure 

 subject I may refer to a valuable paper by the late Dr. Henry 

 upon the application of heat to disinfection, in which it is 

 proved that a temperature of 2 12 is destructive to such con- 

 tagious matters as could be made the subject of experiment.* 



The compounds of nitrogen with oxygen are the following : 



Nitrous oxide or protoxide of nitrogen . . . NO 



Nitric oxide or deutoxide of nitrogen .... NO 2 



Nitrous acid (hyponitrous acid of Turner) . . . NO 3 

 Peroxide of nitrogen (nitrous acid of Turner, hyponitric 



acidofThenard) NO 4 



Nitric acid NO 5 



* Phil. Mag. 2nd Series, v. 10, p. 363, and vol. 11, pp. 22, 207, (1832.) 



