384 Nature and Properties of Azotic Gas. [Book V. 



4thly. Azotic gas is rendered refpirable by vegeta- 

 bles, which, in certain circumftances, furnifh vital air. 

 This property is probably owing to their retaining the 

 hydrogen of the water which they abforb, while they 

 part with the oxygen. There is no doubt that azotic 

 gas is really a conftituent principle of the atmofphere; 

 for if feventy-thrre parts of it are mixed with twenty- 

 feven of pure air, an air will be produced refembling 

 that of the atmofphere, and refpirable as that is *. 



5thly. It is now a well eftablifhed fact, that the 

 azote, or bafis of phlogiilicated air, is literally the bafis 

 of the nitrous acid f j for being mixed in proper pro- 

 portions with oxygen or pure air, which is neceflary to 

 give to thefe bafes the acid character, and fet on fire 

 by palling through them an electric fpark, nitrous acid 

 is uniformly produced, as is evident from the experi- 

 ments of Mr. Cavendifh. 



6thly. Late difcoveries have alfo evinced, that the 

 volatile alkali is formed from a union of this gas with 

 hydrogen, or inflammable air. 



As this air conftitut.es fo large a proportion of the 

 common air which we breathe, its further ufes and 

 properties will be better explained when I come to 

 treat of the atmofphere. 



* Briflbn, torn. ii. p. 3 5. 



f It may perhaps be neceflary to inform the young reader, that 

 nitrous acid is that fubftance commonly fold in the Ihops under the 

 name of aquafortis. It may feem furpriiing to be tcdd, that the air 

 which we are commonly breathing is effentially aqua fortis But 

 though that extremely corrofive and deadly fluid is really com-* 

 pofed of azote and oxygen, yet they are then in a ftate of cofr* 

 , whereas in aynofpheric air they are only mix-:d. 



