200 NITROGEN. 



it is very small ; caustic potash remained dry on the peak of Ten- 

 erifFe, at 12,176 feet above the sea. 



(b.) These adventitious things probably vary in their proportion. 



(c.) Besides these, there are other bodies. 



Various inflammable gases, from marshes and stagnant waters, 

 from putrefaction, &c. 



Jlmmonia, from the latter cause, and from some plants. 



Vapors and effluvia, from every volatile thing, from fluids, flowers, 

 &c.producmg odors and aroma. 



The matter of contagion. It is too subtile as yet for our processes, 

 doubtless it is something aerial, more subtile than any gas yet known. 

 It is combated successfully by chlorine, and to a degree, by acid gases. 



" Seguin examined the infectious air of a hospital, the odor of 

 which was almost intolerable, and could discover no appreciable de- 

 ficiency of oxygen, or other peculiarity of composition." Turner. 



Upon the usual estimation of 21 per cent, of oxygen in the air, its 

 contents will be, including only those bodies whose existence has 

 been proved to be constant. 



Nitrogen gas, 77.5 by measure, 75.55 by weight. 



Oxygen gas, 21. " 23.32 " 



Aqueous vapor, 1.42 " 1.03 



Carbonic acid gas, .08 " .10* " 



Dr. Prout discovered that the specific gravity of any gas is ob- 

 tained by multiplying its combining weight by .555, which is half the 

 sp. gr. of oxygen gas, air being 1. or 10. ; half the sp. gr. of oxygen 

 is taken because half a volume of oxygen represents its combining 

 power. The above rule applies to gases whose equivalents are es- 

 timated with reference to oxygen as unity ; if hydrogen be unity, 

 then multiply the equivalent by that scale, by .555 as before, and di- 

 vide the product by 8, which is the combining weight of oxygen upon 

 that scale. Or the same result will be obtained by multiplying the 

 equivalent upon the hydrogen scale, by the number expressing the 

 sp. gr. of hydrogen, namely, 0.0694. Id. 



Remarks. 



If we could suppose our atmosphere to be removed, (the laws of 

 heat and of pressure remaining as they now are,) another atmosphere 

 would be immediately formed, consisting of aqueous vapor, and of 

 every thing else that could, at the given temperature, assume the ae- 

 riform condition 5 this process would go on until the pressure react- 

 ed with sufficient power to become mechanically a substitute for the 

 present atmosphere. With similar physical laws, we cannot there- 

 fore understand, how any of the heavenly bodies can be without at- 

 mospheres, of some kind or other. 



* Murray, I, 433. 



