1806. 
diftin&. In order to attain the firft object, 
it is aflumed that the denfity and elafic 
force of each gas at the earth’s furface are 
the effeéts of the weight of the atmofphere 
ef that gas only, the different atmofpheres 
not gravitating one uponanother. Hence 
it is neceffary to aflcerytain what fhare of 
elafiic force is due to each gas in a given 
volume of the compound atmofphere, to 
find how much the given volume is dimi- 
nifhed under a contant preffure by the ab- 
ftvaétion ot each of its ingredients fingly. 
Thus if by extracting the oxygenous gas 
from any ma{s of aimofpheric air, the 
whole isdiminifhed one-fifth in bulk, fup- 
pofing the preffure to be equal to 30 inches 
of mercury, then it muft be inferred that 
the oxygenous atmolphere preffes on the 
earth with a force of fix inches of mer- 
cury. ‘To afceriain the fecond po: t, the 
fpecific gravity of each gas mult be ob- 
tained, tor the weight of each gas in any 
given portion of atmofpheric air mutt. be 
in the compound ratio of its force and 
{pecific gravity. With regard tothe third 
object, it may be obferved, that thofe 
gafes which are fpecifically the heavieft, 
mutt decreafe in denfity the quickelt in 
afcending. The feveral gafes conitantly 
found in atmofpheric air, and in fuch quan- 
tilies as are capab'e of being appreciated, 
are azotic, oxygenous, aqueous vapour, 
and carbonic acid. It is probable that 
hydrogenous gas is alfo conttantly pre- 
fent; burt in fo fmall a proportion as not 
to be detected by any teit with which we 
are acquainted: hence Mr. D. confcunds 
it in the mals of azotic gas. 
He now proceeds to mention the various 
procefles ufed to determine the quantity 
of oxygenous gas: 1. By a mixture of 
nitrous gas and air over water. 2. By 
expofing the air to liquid {uloburet of 
potaih or lime. 3. By exploding hydro- 
gen gas and air by eleétricity. 4. By 
expoling the air to a folution of green ful- 
phat or muriat of iron in water, flrongly 
impregnated with nitrous gas. 5. Burn- 
ing phofphorus in the air. In all thefe 
cafes the oxygen enters into combination 
and Jofes its elatticity ; and if the {e- 
veral proceff:s be well conduéted, the re- 
fultsin all are precifely the fame. Mr. 
D. fieds from experiments, that in all 
places and every jeafon cf the year, the 
bulk of any given quantity of atmo- 
{pheric air appears to ve reduced nearly 
21 per cent. by abflraéting its oxygen: the 
weight of the aqueous vapour in the atmo- 
{phere he reckons to be equal to .443 of 
mercury; or, nearly 75h of the whole 
Proceedings of Learned Societies. 
23 
atmofphere ; that of carbonic acid gas to 
be only about the ~j.,th part of the 
whole in bulk, but fince the f{pecific gra- 
vity of this gas is 13 that of common air, 
the weight of the carbonic acid gas is 
nearly zo'55 part of the whole. 
Mr. D. next gives a table, containing 
the {pecific gravities of the different gafes, 
takeo from Kirwan, Lavoifier, and Davy, 
it is as follows: 
Atmofpheric air = - 1.000 
Azotic gas - = - - .966 
Oxygenous - - - - 1.127 
Carbonic acid gas - - 1.500 
Aqueous vapour - = «700 
Hydrogenous gas - - <077 
From thefe data are formed the tollow- 
ing tables. 
I, Tabie of the weights of the differ- 
ent gafes conftituiing the atmofphere. 
aches of Mercury. 
AZM Bas i520) 5 23438 
Oxygenous gas - - - 6.18 
Ayueous vapour - - 44, 
Carbonic acid-gas - - 02 
30.00 
IT. Table of the proportion of weights 
of the different gafes in a given volume 
of atmofpheric air, taken at the furface 
of the earth. 
per Cent. 
AZOIC Bas = ee aia 
Oxygenous gas - - - %3.32 
Aqueous vapour = - 1.03 
Carbonic acid gas + - 210 
100.00 
{ 
With refpe& to the proportion of gales 
at different elevations, Mr. D. thinks 
that the oxygenous gas obferves a dimi- 
nifhing ratio in afcending ; and hence, tak- 
ing the azotic atmolphee as a ftandard, 
the oxygenous gas and the carbonic acid 
will obferve a decrealing ratio to it in 
afcending, and the aqueous vapour an in- 
creafing one. The fpecific gravity of 
oxygenous and azcotic gafes being as 7 to 
6 vearly, their diminution in denfity will 
be the fame at heights reciprocally as their 
fpecific gravities. Hence it would be 
found, that at the height of Mount Blanc 
(nearly three miles) the ritio of oxyge-. 
\nous. gas to azotic in 1a given volume of 
air would be nearly as 20 to 80, and con- 
fequently it follows that at any ordinary 
heights the difference in the proporticns 
will be {carcely perceptible. 
REVIz W 
