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LX V. Sequel to an Essai/ on the Constitution of the Atmosphere 

 published in the Philosophical Transactions for 1826; with 

 some Account of the Sulphurets of Lime. By John Dalton, 

 D,C,U, F.R.S. Sfc, 



[Continued from p. 168, and concluded.] 

 On the Quantity of Oxygen in the Atmosphere, 



SINCE the commencement of the present 'century it has 

 been ascertained beyond dispute that the chief constitu- 

 ents of the atmosphere, oxygen gas and azotic gas, are in the 

 same proportion in all countries and at all times, except when 

 influenced by local circumstances; namely, 21 percent, of 

 volume of oxygen, and 79 per cent, of azote, neglecting frac- 

 tions : other elements are found in the atmosphere, but they 

 are comparatively insignificant in quantity, namely aqueous 

 vapour, carbonic acid, &c. The experiments have generally 

 been made on air collected at the surface of the earth ; and 

 it may be remembered that I have endeavoured to prove in 

 various essays that the diffusion of gases one amongst another 

 as well as iii vacuo, is owing to the repulsive powers peculiar 

 to the particles of each particular gas, otherwise we should 

 never have the feeble efforts of carbonic acid and aqueous 

 vapour diffusing those elements against the immense pressure 

 of the atmosphere. The principle I contend for has, I be- 

 lieve, obtained general assent; but I apprehend few have 

 been aware of the consequences. If we suppose a carbonic 

 acid atmosphere of 15 inches of mercury pressure and a hy- 

 drogen atmosphere of the same pressure, together constituting 

 a mixture of the two amounting to 30 inches of pressure, were 

 to surround the earth, I think no one would hazard a con- 

 jecture that these two would be found in equal proportions at 

 every elevation in the atmosphere ; yet a similar supposition 

 seems prevalent with regard to our present atmosphere of 

 oxygen and azote. It has been an object of investigation with 

 me for many years to find how the fact stands in this respect ; 

 that is, whether the oxygen is more abundant relatively in 

 the lower strata of the atmosphere than in the higher, as it 

 ought to be in a stagnant column ; or whether the constant 

 agitation of the atmosphere and the predominant mechanical 

 power of the azotic part of it do not prevent that equilibrium 

 which a stagnant mixture of aerial fluids of different specific 

 gravities would effect. From the experiments about to be 

 related, I have reason to believe that the higher regions of 

 the atmosphere are somewhat less abundant in the proportion 

 of oxygen than the lower, though the reverse might be ex- 

 pected from the enormous consumption of oxygen by daily 

 processes on the surface of the earth, when we know of no 



