398 Dr. Dalton on the Constitution of the Atmosphere, 



proportionate consumption of azote. It appears, however, 

 that the disproportion of the two elements at different eleva- 

 tions is by no means so great as theory requires ; and there- 

 fore we must conclude the unceasing agitation of the atmo- 

 sphere by currents and counter-currents is sufficient to main- 

 tain 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, v/hich, as long ex- 

 perience has taught me, require attention in order to secure 

 a due approximation 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 

 proportion 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 hy- 

 drogen by oxygen gas. It is best not to rely too much upon 

 hydrogen taken from a bottle half filled with water. 



^. Oxygen gas, and others, will show carbonic acid by send- 

 ing them up through a narroweudiometer tube filled with lime- 

 water, provided the acid gas amounts to | per cent, of the ori- 

 ginal; but it does not show any carbonic acid in this way in at- 

 mospheric air, though the acid is always present to the amount 

 perhaps of y qVo^^ P^^^* '^^^ proportion of pure oxygen in 

 any sample containing from 90 to 100 per cent, of that gas, 

 may be found either by hydrogen gas or nitrous gas; and if 

 great accuracy is required, I recommend testing it both ways, 

 as has already been mentioned under the head nitrous gas. 



3. The gradual deterioration of oxygen, hydrogen, nitrous 

 gas, common air, &c. when by use the phial became j, ~, or 

 I filled with trough water, is a circumstance by no means to 

 be overlooked. The entrance of water that has been some- 



