THE ELEMENTS OF COMMON AIR. 147 



tnena of combuftion in air, and in oxigen is not to be afcribed Afcrlbed merely 

 to the combination of azot and oxigen, but to the lefs denfity \° ^J^. ^^"^1°"^ 



■^ ' ^ denfities of ox- 



of the latter, (-i) of what a pure atmofphere of the fame gas jgen in which 



would be. From an incidental but iraperfed trial I made, in ^^''-^y ^^^^^ '° 

 conjun6tion with Mr. Davy lafl winter, I have no doubt but 

 iron wire would burn in common air of five times the denfity 

 with brilliancy as in an atmofphere of pure oxigen of common 

 denfity. At any rate it is notorious that as the denfity of com- 

 mon air is increafed, combufiion in it becomes more vigorous. 

 Though I have never attempted combuftion in an atmofphere Propofed expe,- 

 of pure oxigen of i. the common denfity, I can fcarcely doubt [j^fs'^^-mT.'^"'''* 

 that the appearancees would be much the fame as in the open 

 air. It is probable therefore that the facts under this head, if 

 duly inveftigated, would turn out in favour of the hypothefis 

 of air being a mixture. 



4. •' A gas no way diftinguithable from common air fre- 4. Gas refem- 

 quently makes its appearance during the preparation of nitric b'mg common^ 

 acid; and Mr. Davy decompofed nitrous oxide, by paffing it preparing nitrous 

 through a red hot tube, andconverted it into nitric acid and a ^'^''^" 

 gas, which poflefled the properties of common air; now if air 

 were a mere mixture, it is infinitely improbable that its two 

 confiituent parts fliould be evolved during fuch procefifes ex- 

 adtly in the proportion that exifts in common air." — Granted; 

 but as the force of this argument refts upon the exaSt propor- 

 tion of oxigen and azot in the gafes fo evolved, that is, upon 

 their being conflituted always of 21 percent, oxigen, and 79 

 azot, the fa£ts fliould be made out accordingly. Dr. Prieflley Anfwer. The 

 is the only one I know of, who has particularly examined tlie PJ^^''"^ refem- 



-' ' ^ ■^ blance, or pro- 



gas produced in the preparation of nitric acid, and he found it portion of parts, 



to have much more oxigen than common air. Mr. Davy in his \^^ "'^"^ ^^^" 



, „ , Ihewn. 



analyfis of nitrous oxide, found the gas 'analogous to atmo- 



fpheric air always to contain lefi oxigen, though it was nearly 



of the atmofphericflandard. 



The quick afcent of hidrogen and the defcent of carbonic The ftatical 



acid, have been objeded to my hypothefis as fads that prove ^["J^ ""^^^f "'J*' 



the operation of the laws of Ipecific gravities on elaftic fluids, foros no proof 



No doubt can exifl that a portion of elaflic fluid completely 'jf^^^^J;'^ ^^"^ 



infulated, as a balloon, or a bubble of carbonic acid or hidro- aiftufion" 



gen, furrounded by a film of water, is fubjedl to the laws of 



gravitation, and rifes or falls in elaflic fluids on the fame prin- 



L 2 ciple 



