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XIX. Sequel to an Essay 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.L., F.R.S., 8$c. 
Received June 9, — Read June 15, 1837. 
In an essay of mine on the constitution of the atmosphere, which was printed in 
the Transactions for 1826, I signified my intention of following it with a sequel of 
experiments to ascertain if possible which of the two views therein developed was 
most countenanced by facts. I now proceed to give an account of such investiga- 
tions relating to this subject as have engaged my attention during a long period of 
years. 
It may be needful to premise certain facts which are, I believe, universally ad- 
mitted as indisputable ; namely, that the atmosphere consists principally of two elastic 
fluids, azote and oxygen, either mixed by some mechanical law, or otherwise com- 
bined by a chemical principle in proportion nearly as four parts of the former to one 
of the latter in volume ; that the two elastic fluids may be obtained separately in 
a state of purity ; that when thus obtained they may be mixed in all possible propor- 
tions; and that the aggregate volumes in such cases are just equal to the sum of the 
two volumes of the ingredients : also, that any body which has a chemical affinity 
for either of them so as to combine with it in a separate state, will also combine with 
it in the mixed state. 
It is also pretty generally admitted that oxygen and azote are capable of chemical 
combinations in five or more definite proportions, namely, 
2 vol. of azote with 1 vol. of oxygen — forming 2 vol. of nitrous oxide. 
1 vol. of azote with 1 vol. of oxygen — forming 2 vol. of nitrous gas. 
1 vol. of azote with 1^ vol. of oxygen — forming 1^ vol. of hyponitrous acid. 
1 vol. of azote with 2 vol. of oxygen — forming 2 vol. of nitrous acid vapour. 
1 vol. of azote with 2^ vol. of oxygen — forming 2|- vol. of nitric acid. 
There does not appear to be a doubt of the reality of five combinations, but all 
chemists are not agreed as to the proportions of the volumes being precisely as above 
specified, chiefly because no general law has been found to obtain in such gaseous 
compounds. 
These compounds are never formed nor decomposed without manifest chemical 
agency ; they all contain oxygen, but no portion of it can be abstracted from any 
one of them without some chemical operation ; whereas nitrous gas will immediately 
seize the oxygen from any of the aforementioned mixtures, the same as if it was alone, 
2 z 
MDCCCXXXVII. 
