356 
DR. DALTON ON THE CONSTITUTION OF THE ATMOSPHERE. 
should never have the feeble efforts of carbonic acid and aqueous vapour diffusing 1 
those elements against the immense pressure of the atmosphere. The principle I 
contend for has, I believe, 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 hydrogen atmosphere of the same pressure, together con- 
stituting a mixture of the two amounting to 30 inches of pressure, were to surround 
the earth, I think no one would hazard a conjecture 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 experi- 
ments 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 expected from the enormous consumption of oxygen by 
daily processes on the surface of the earth, when we know of no proportionate con- 
sumption of azote. It appears, however, that the disproportion of the two elements 
at different elevations is by no means so great as theory requires ; and therefore we 
must conclude the unceasing agitation of the atmosphere by currents and counter- 
currents is sufficient to maintain an almost uniform mixture at the different elevations 
to which we have access. 
The subject is one involving an important principle. I have kept it continually 
in view for the last forty years, and have made innumerable experiments with a view 
to its elucidation. As the value of such experiments depends much upon a thorough 
acquaintance with the nature of the operations and the several sources of error to 
which they are liable, it may be needful to point out certain particulars, which, as 
long experience has taught me, require attention in order to secure a due approxima- 
tion to accuracy. I allude more particularly to the use of Volta’s eudiometer as 
applied to determine the proportions and quantities of oxygen and hydrogen gases. 
1. Hydrogen gas procured over water is sure to contain some common air, whether 
the water has been previously boiled or not ; it arises out of the water and may 
amount to 1 or 2 per cent. ; the same observation applies to oxygen gas ; the pro- 
portion of oxygen and azote is usually that in common air nearly. When a phial of 
hydrogen gas, by long keeping or by accident, has acquired a portion of common 
air, and then stood some weeks after, the oxygen seems to diminish, either by slow 
combustion or by absorption in the water, and so leaves the azote and oxygen in 
another proportion to that of common air. Before using such hydrogen the oxygen 
in it should be tested by nitrous gas, and the percentage of hydrogen by oxygen gas. 
