1820.] Specific Gravity of Gases. 163 



of Gay-Lussac's law, and to establish the ratios between the 

 weights of their ultimate atoms. These four gases are o.vi/o-e?i, 

 azote, hi/drogeii, and c/ilorine. 



1. Oxygen and azote mixed together in a determinate propor- 

 tion constitute atmospherical air. Now it was shewn bv Dr. 

 Prout, in a former volume of the A/iiia/s of' l*hilo!ioi>lnj, that if 

 the specific gravity of air be 1 000, and if air be a mixture of four 

 volumes of azotic and one volume of oxygen gases, then the 

 specific gravity of these two gases is as follows : 



Oxygen gas Mill 



Azotic gas 0-9722 



This hypothesis does not accord completely with the analysis 

 of atmospherical air, as hitherto made by the most careful expe- 

 riments. The present opinion entertained is that air is a mixture 

 of 79 volumes of azotic and 21 volumes of oxygen gas. If air be 

 a mixture of 80 volumes of azotic and 20 voluufes of oxygen, then 

 it follows that it consists of two atoms of azote and one atom of 

 oxygen, probably in chemical combination. Nov/ the very close 

 approximation of the experimental result to 80 and 20 leaves httle 

 doubt in my mind that air is really a chemical compound of two 

 atoms of azote and one atom of oxygen. When I attei^ipted to 

 analyze common air by abstracting its oxygen by means of a 

 stick of phosphorus, 1 have never been able to satisfy myself, 

 though 1 have repeated the experiment above 100 times, that 

 the diminution of bulk is not exactly one-fifth of that of the 

 whole air acted upon. But when 100 volumes of air are mixed 

 Avith 42 or 44 volumes of hydrogen gas, and an electric spark 

 passed through the mixture, the diminution of bulk always 

 amounts to 63 volumes. Now as this diminution is occasioned 

 by the formation of water, which is a compound of tuo volumes 

 hydrogen and one volume oxygen, it is obvious that one-third ot 

 the diminution of bulk must be oxygen. This gives us 21 volumes 

 for the bulk of oxygen contained ni 100 volumes of air ; but I 

 think it very probable that when air is analysed by the combus- 

 tion of hydrogen gas some nitrous acid, or ammonia, is always 

 formed, which would of course diminish the quantity of azote, 

 and render the residual volume less than it ought to be. 



The specific gravities of oxygen and azotic gases taken with 

 as much accuracy as possible in my laboratory were fuund to be 

 as follows : 



Jiy tirst trial 1-1 117 



By second trial 1-1117 



By tliird trial 1- 1 1 17 



7> n . Azotic ga«. 



i^y first trial 0-9730 



By second trial 0-9728 



By third trial ', 0-9728 



l2 



