185) On the Chemical Compounds of (Marcu, 
two essays in the Manchester Memoirs (vol. i. second series, 1805),, 
and, some. essays in Nicholson’s Journal: (vol. viii. ix. x. 1804-5), 
all of which were intended to support the opinion of atmospheric 
air being a chemical compound. ‘The last mentioned author does 
not avail himself of the two affinities, the strong and the weak, in 
order to explain the phenomena of mixed gases. 
Lhave animadverted upon the opinions of some of these authors 
in the above volumes of the Journal, and more particularly in the 
first part of my chemistry (1808), in which I have materially modi- 
fied the mechanical hypothesis of mixed gases first published in 
1802. Since 1808 there has not, to my knowledge, been much 
written on the subject of mixed gases. 
Sir Humphry Davy’s Elements of Chemical Philosophy appeared 
in 1812; and it might have been presumed, from the great progress 
made in chemistry within the last few years, that some addition 
would have been made to our knowledge of the constitution of the 
atmosphere since his Researches published in 1800; but I find no 
allusion to his before-mentioned notion of the air being a chemical 
compound of azote and oxygen, or to the evidences of it. At 
p- 231, it is observed, that “ if four parts of azote be mixed with 
about one part of pure oxygen gas;. they constitute a mixture re- 
sembling exactly atmospheric air;”” and as no mention is made of 
atmospheric air, when treating of the compounds of azote and 
oxygen, it seems to be tacitly implied that this author no longer 
considers atmospheric air as a chemical compound. 
Dr. Henry introduces the subject of atmospheric air into his 
Chemistry as follows: “ The air of our atmosphere, it appears, 
from the facts stated in the preceding section, is a mixture, or. pos- 
sibly a combination, of two different gases, viz. oxygen gas and 
azotic gas.” 
Lastly, Gay-Lussac has recently written an essay on the com- 
pounds of azote and oxygen, amongst which he has not mentioned’ 
atmospheric air. 
These observations seem to show that the opinions of philosophers 
are far from being uniform in regard to the nature of mixed gases 
in general, and of the atmosphere in particular. Indeed, it is 
difficult to ascertain what is the most prevailing opinion. In 1807 
Dr. Thomson made the following observation: ‘‘ Mr. Dalton con- 
siders air as merely a mechanical mixture of the two gases of whieh 
it is composed. But all other chemists consider: it as a) che- 
mical compound.” (Chemistry, iv. 68.) Whereas a writer in the 
Annals of Philosophy (1815) observes, that ‘* chemists do not 
appear to have considered atmospheric air in the light of a com- 
pound formed upon chemical principles, or at least little stress has 
been laid on this circumstance.” 
Whatever may be the ultimate opinion of chemists respecting 
the infinite variety of mixtures of azote and oxygen, it is clear, I 
think, that they never can be classed as compounds of azote and 
oxygen, along with nitrous oxide, nitrous gas, &c. which possess 
