PROFESSOR GRAHAM ON THE MOTION OF GASES. 
589 
following- experiments the height of the barometer was 29'3 inches, which is the value 
of 1 atmosphere, and the thermometer 53°. 
Table VI. — Effusion of Air of different Densities. 
Height of 
gauge barom. 
Air of 1 atmo- 
sphere. 
Air of 
1-25 atmosphere. 
Air of 
1‘5 atmosphere. 
Air of 
1 • 75 atmosphere. 
Air of 
2 atmospheres. 
Air of 
1 atmosphere. 
in inches. 
I. 
II. 
I. 
II. 
I. 
II. 
I. 
II. 
I. 
II. 
III. 
IV. 
✓/ 
// 
// 
// 
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// 
n 
// 
// 
// 
// 
28 
0 
0 
0 
0 
0 
0 
0 
0 
0 
0 
0 
0 
20 
116 
116 
90 
91 
76 
75 
65 
65 
56 
55 
117 
117 
12 
118 
118 
92 
91 
76 
76 
64 
64 
56 
56 
118 
118 
8 
65 
63 
47 
48 
38 
38 
33 
33 
30 
29 
66 
67 
4 
79 
80 
30 
50 
41 
40 
33 
32 
26 
28 
80 
80 
2 
54 
54 
26 
25 
18 
18 
16 
17 
14 
13 
54 
53 
432 
433 
305 
305 
249 
247 
211 
211 
182 
181 
435 
435 
In these experiments the depression of the gauge barometer is not produced by a 
constant volume of the compressed air, but by a volume which is inversely propor- 
tional to the density of the compressed air ; half a volume of air of 2 atmospheres 
being equal in the aspirator-jar, on the plate of the air-pump, to a whole volume of 
air of 1 atmosphere. Correcting the times of the preceding table, we have the pas- 
sage of equal volumes of air of different densities, between the gauge height of 28 and 
12 inches, as follows : — 
Time of effusion of equal volumes. 
Air of 1 atmosphere .... 234*5 seconds . . 1 
Air of T25 atmosphere .... 227*5 seconds . . 0*9/01 
Air of 1 *5 atmosphere .... 227*2 seconds . . 0*9688 
Air of 1*75 atmosphere .... 225*2 seconds . . 0*9603 
Air of 2 atmosphere .... 223 seconds . . 0*9510 
It appears then that air of different densities between 1 and 2 atmospheres is 
effused in nearly equal times, the time of effusion diminishing slightly, not more than 
5 per cent, with air of double tension. Taking the whole range of the preceding 
and present results, we have air varying in density from 0*25 to 2 atmospheres, or 
from 1 to 8, while the extreme variation in the time of the effusion of equal volumes 
is from 0*9510 to 1*1287, or from 1 to T1868. 
In the lower part of the scale a more sensible inequality is perceived. Thus, with 
an exhaustion of from 8 to 4 inches in the aspirator-jar, the passage of equal volumes 
of air of different densities takes place in the following times : — 
Air of 1 atmosphere . . 
Time of effusion of 
. . 145 seconds 
equal volumes. 
. . 1 
Air of 1*25 atmosphere . . 
. . 121*9 seconds 
. . 0*8407 
Air of 1*5 atmosphere . . 
. . 117*7 seconds 
. . 0*8117 
Air of 1*75 atmosphere . . 
. . 114*6 seconds 
. . 0*7903 
Air of 2 atmospheres . . 
. . 113 seconds 
. . 0*7793 
