348 
DR. DALTON ON THE CONSTITUTION OF THE ATMOSPHERE. 
whatever may be the proportions. Atmospheric air itself, or any artificial mixture 
of the two gases in the same proportion as common air, is equally affected by 
nitrous gas and by every other agent. 
Waving at present any consideration as to the nature and properties of the above 
chemical compounds, 1 shall now proceed to state the means by which the propor- 
tions of oxygen and azote in mixtures of these two gases may best be determined. 
Having been engaged in this investigation occasionally for more than forty years, I 
may be entitled to give my opinion on this important subject in practical chemistry. 
Various methods of analysing common air have been discovered in the last fifty 
years. I have principally directed my attention to three, namely, (1.) by the use of 
Volta’s eudiometer and hydrogen, or (2.) by nitrous gas, or (3.) by quadrisulphuret 
of lime, to abstract the oxygen from the azote. 
First Method , by Volta’s Eudiometer . 
Mr. Cavendish was one of the first to investigate the changes produced by firing 
mixtures of hydrogen and common airs in various proportions. (Vid. Philos. Trans., 
1/84.) The following Table will exhibit a lasting monument of his skill in effecting- 
such an investigation. Many have attempted since to improve the methods of ana- 
lysis, and have brought out results widely differing from those to be derived from his 
table ; but it is now universally allowed that his results are nearer approximations to 
the truth than most of those we have seen since. 
His method was to take 100 measures of common air and mix them with various 
proportions of hydrogen, beginning with upwards of 100, and gradually descending 
till about 20 ; then, firing each mixture by an electric spark, he marked the diminu- 
tion of the mixture each time as under. 
The following results are extracted from Mr. Cavendish’s Table, except the last 
column, “Amendment,” which I have attached, for reasons assigned below. 
Exp. Common Inflammable Diminution Amendment. 
Air. Air. on firing. 
]. . . 100 measures mixed with 1 24-* 1 .... gave . . . 68‘6 ..... 66‘3 
2. . . 100 105-5 .... . . . 64-2 65‘8 
3. . . 100 70-6 .... . . . 64-7 ..... 64-9 
4. . . 100 42-3 .... . . . 61-2 ..... 60‘6 
5. . . 100 33-1 .... . . . 47‘6 ..... 47-4 
6. . . 100 20-6 .... . . . 29-4 ..... 29'5 
In the first three experiments no oxygen was found in the residuary gas ; in the 
fourth a trace of oxygen was found ; and in the fifth and sixth, considerable quanti- 
ties of oxygen were found in the residues. 
It is obvious that Mr. Cavendish began intentionally with an overdose of hydrogen, 
probably expecting the diminution to be a constant quantity till the hydrogen became 
deficient, and then of course the diminution must be lessened ; this was not the case 
