PROFESSOR GRAHAM ON THE MOTION OF GASES. 
581 
3. Effusion of Nitrogen and Oxygen , and of mixtures of these Gases under different 
pressures, hy a second perforated brass plate B. 
This brass plate was of the same thickness as the last (^gth of an inch) ; the aper- 
ture was circular and also -^Ts' th of an inch in diameter, as measured by a micrometer ; 
and the velocity with which air of the usual tension passed into a vacuum by the 
aperture, one cubic inch in 6*08 seconds. The rate of passage was therefore rather 
more than twice as quick as by the first perforated plate A. 
A two-pint jar was used as the air-pump receiver, or aspirator-jar, as it may be 
called ; and the capacity of the vacuous space into which the gas effuses, including 
the tubes and channels of the air-pump as well as the jar, was found to be 72*54 
cub. in. An exhaustion was always first made of about 29 inches by the gauge baro- 
meter of the pump, and then the gas allowed to enter from a counterpoised bell-jar 
over water (fig. 1, Plate XXXIII.). The instant was noted at which the mercury fell to 
28 inches, when the observation began, and again at 20 and 12 inches, or after two in- 
tervals of 8 inches each ; and again at 4 and 2 inches by the gauge barometer. The ex- 
periments were made successively on the same dayin the order given, with the barometer 
at 29*34 inches and thermometer at 49°. A small thermometer placed within the 
aspirator-jar was observed to rise 1 ° Fahr. very uniformly during the continuance of 
an experiment. The effusion of air is repeated at the close of the experiments to de- 
termine whether or not any change of rate had occurred during their continuance. 
Table I. — Effusion. 
Gauge barometer in 
inches. 
Air. 
Nitrogen. 
Oxygen. 
Mixture of 
50 nitrogen + 50 oxygen. 
1. 
II. 
1. 
11. 
I. 
II. 
I. 
II. 
// 
// 
// 
✓/ 
// 
28 
,0 
0 
0 
0 
0 
0 
0 
0 
20 
120 
120 
119 
119 
126 
126 
122 
122 
12 
123 
122 
120 
120 
128 
130 
125 
125 
8 
68 
68 
67 
67 
72 
72 
70 
69 
4 
84 
84 
83 
83 
89 
88 
85 
86 
2 
37 
57 
55 
54 
59 
59 
57 
57 
452 
451 
444 
444 
474 
475 
459 
459 
Table II. — Effusion. 
Gauge barometer in 
inches. 
25 nitrogen + 75 oxygen. 
75 nitrogen + 25 oxygen. 
Air. 
I. 
II. 
I. 
II. 
28 
// 
0 
// 
0 
// 
0 
0 
0 
20 
122 
122 
122 
121 
120 
12 
125 
125 
122 
122 
123 
8 
70 
69 
68 
68 
68 
4 
85 
86 
85 
85 
83 
2 
57 
57 
56 
56 
57 
459 
459 
453 
453 
451 
